I want to replace my boiler. Please help!
Last Post 19 Apr 2011 02:47 PM by Dana1. 33 Replies.
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whatAreMyOptionsUser is Offline
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04 Apr 2011 01:53 PM
I live in CT and currently have an oil boiler that provides DHW and heats the home via copper baseboard pipes (hydronic). With oil prices shooting up, I am fed up. My oil burner was installed with the home in 1994 and is very inefficient. I resorted to heating 2 of the 3 zones during the winter to keep the oil consumption down. What options do I have for getting rid of oil and splitting my DHW off into an electric water heater w/tank and keeping the hydronic baseboard heat? Natural gas is not an option unfortunately. My budget is $10,000 not including any federal and state credits/rebates. I have requested a quote from a local HVAC company for a geothermal system knowing full well it will not fit into my budget, but I'm just curious at this point. The biggest problem I'm having is finding reputable installers. It's easy to find installers for oil boilers, but for the environmentally friendly stuff it's a crap shoot. I have even entertained a wood boiler. Any of my options would need to be installed by a professional as I'm not a DIYer.


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04 Apr 2011 06:02 PM
How much oil/year are you currently using, and how big is your house?

To get a handle on your actual vs. rated AFUE, down load and carefully check with the NORA FSA Calculator downloadable here:

http://nora-oilheat.org/site20/fsa/FSACalculator_1_1_0_8.zip

the manual for the software lives here:

http://www.nora-oilheat.org/site20/uploads/copier@eeacompanies%20com_20110111_150909.pdf

If yours is like most homes, you can get a significant bang/buck out of a round of air-sealing (with calibrated blower-door test & verification), and spot-insulation (with infra-red camera testing & verification). There are likely subsidies to be reaped from the state & feds for any upgrading. If your basement, foundation sill & band joist aren't insulated, foam sealing the sill & joist and insulating the basement walls would likely result in a 15-20% fuel savings-sometimes more. (Careful how that's done- you don't want to create moisture or mold problems by driving ground moisture higher in the insulation or any interior studwall or allowing wintertime condensation to form. See: http://www.buildingscience.com/documents/information-sheets/5-thermal-control/basement-insulation/files/bscinfo_511_basement_insulation.pdf )

Only with all the low-hanging fruit is thoroughly plucked clean would spending money on a full heating system swap make sense, and the size & cost of any new system would be significantly reduced by the now-lowered peak heat load. If you spent half the money on weatherizition and insulation upgrades you MIGHT be able to spend the rest on a tank-based condensing propane combi boiler for both heat & hot water, but you're right, you won't be able to touch even half of a geo system for $10K. Unless the oil boiler is on it's last legs upgrading the envelope and re-commissioning the boiler (maybe with indirect fired hot water, or reverse-indirect buffer/hw heater replacing the lo-efficiency embedded coil- see: http://www.nora-oilheat.org/site20/uploads/FullReportBrookhavenEfficiencyTest.pdf ) might be the right course.

With a buffer tank or reverse-indirect and re-plumbing the heating system primary/secondary you can then slave the boiler to the buffer's aquastat and run the baseboard at lower temp than would otherwise be "safe" for the boiler, and with the mass of the buffer the boiler

A: can be heat-purged into the buffer at the end of a burn with a retrofit controller like an Intellicon HW+ or Beckett Heat Manager for lower standby loss, and

B: Won't "short cycle" with the extra thermal mass of the tank to work with. This would take a competent hydronic designer to work out the details, but with this sort of approach most circa 1994 vintage oil boilers can be made to run at 85% efficiency despite being oversized for the load. If yours is 3x oversized fro the peak load (probably is) it's likely to be running somewhere in the low 70s, for AFUE (maybe lower if you're keeping it at 140F all summer just for hot water), and bumping it up to 85% operation would mean a 20% reduction in fuel use.

If it costs you $5K to re-configure the system to allow lower temp operation (it should be less) for a 20% reduction, and another $5K in insulation upgrades buys you another 20% you're looking at a total net reduction in fuel use of ~36%. (If the boiler craps out on you, replacing it with a "right sized" propane fired cast iron or low-mass copper fin low temp boiler would be cheap relative to a modulating/condensing version, and could be a relatively simple swap. If your baseboards can deliver design-day heat at 120F it's probably worth buying a mod-con though.

For the price of a 4 ton geo system you could probably do a deep energy retrofit on the building envelope and reduce the fuel use by 60-70%. See:

https://www.powerofaction.com/media/pdf/DER_CaseStudy_Belchertown_MA.pdf

https://www.powerofaction.com/media/pdf/DER_CaseStudy_Millbury_MA.pdf

https://www.powerofaction.com/der/

Got a zip code? (For weather data against which to correlate fuel use to get a good handle on the sizing requirements.)


Eric AndersonUser is Offline
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05 Apr 2011 08:57 AM
OK so your basic question is what are your options for a new heating system. Dana has the right approach, reduce demand, then worry about the heating system.

Step #1 is get an energy audit. Go to CL and P or united illuminating and sign up for an energy audit and weatherization. It will cost you 75$ Best deal in town. Included in that should be an assessment of your existing boiler efficiency. Includes a baseline blower door test.
Step 2. Once the house has whatever weatherization upgrades can be done reasonably and quickly as part of the audit package, then you have a reasonable basis for what to do next.
Step 3 Priority #1 is usually building shell upgrades, guided by the audit. After that, then you can think about what the heating system can/should be. Have a blower door test done after the final shell upgrades so you have an accurate # on infiltration.
Step 4. Have the contractors do a manual J calculation for the house using updated numbers for the shell upgrades. Make sure to include infiltration numbers from the blower door test. Also calculate how much baseboard you have and what water temp you need to supply enough heat at design temp.
Your choices for heat are:
1. OIL, either condensing or other
2. propane mod con or standard
3. electric resistance boiler,
4. GSHP, and air source heat pump,
5. wood boiler or pellet stove
6. A combination of the above.
It is a lot to think about. Connecticut has high cost heat, no matter how you get it. Electricity is expensive, heating oil is expensive, propane is expensive. In this state especially, the key to lower bills is an aggressive insulation and airsealing strategy.
Oh and don’t be so quick to jump on installing an electric hot water heater. This is not likely to help much vs a good indirect tank.
When you get the audit, airsealing and insulation done get back to us and we can help you further on boiler upgrades or replacements.

Good luck, it is a worthwhile endeavor but it takes time and thought to get the best bang for the buck.

Cheers,
Eric



Think Energy CT, LLC Comprehensive Home Performance Energy Auditing
whatAreMyOptionsUser is Offline
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05 Apr 2011 09:35 AM
Dana1, I will definitely try that calculator out tonight.

Eric, I plan to go for a loan from CTEnergyLoan.com which requires I get an audit from CL&P. I know they try to get out of doing the blower test, but I will demand it. For $75 this is a no brainer. The only question I have about this is that I use Green Power Inc and not CL&P directly (they still deliver the electricity) and am not sure if that disqualifies me for the $75 audit and eligibility for the CT Energy Loan. Technically I am still a CL&P customer since it is them that I would call for any issues with my power.

Some details about my house:

-zipcode 06706
-The house is nearly 17 years old
-1670 sq. ft., three floors/zones which is including basement
-The basement is finished and insulated
-I've already got double pane windows
-2.5 bathrooms

One of my goals is to be able to turn off the home heating boiler during the summer. As it stands right now, I obviously have to leave my oil burner running during the summer for the DHW. With a filled oil tank from May 1st and all heating zones shut off, I use about 3/4 of a tank from May 1st to late October when the next fill-up occurs. I would love to keep a full tank from May 1st until the following cold season.

I have toyed with the idea of getting a tankless electric hot water (on demand) heater for all DHW. Does anyone in the north east have any experience with one of these? Do you recommend it? Right now I am leaning towards an electric WH with tank, or an indirect WH. If I plan to turn off the boiler during the warm months, I have to go with a water heater that uses another heat source and can't use an indirect WH, correct?

Can anyone recommend a good site for finding reputable HVAC contractors?

Thanks for the replies!


Eric AndersonUser is Offline
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05 Apr 2011 12:01 PM
OK so lets get down to some numbers. These are just educated guesses based on limited info. (and my math is always sketchy anyway)
¾ of a 270 gal oil tank is ~202 gallons of oil. At 100% efficiency that would be 202 X138,000 btu = 27.8 Million btu’s used for DHW in 7 months.
The realistic efficiency of the boiler in this mode depends on a lot of things, but lets use 50% in summer mode. Without more details about the system, you can’t give too good an estimate for this. If we said net usage of energy for hot water was 14 Million btu’s for 7 months that gives ~24 million btu’s of hot water usage per year, 2 million/month if we assume incoming water is 55° and water is used at 115° the delta is 60° so to heat 1 gallon takes 60°* 8 lbs/gallon= 480 btu/s. 2,000,000 btu’s/month/ 480 btu’s per gallon = ~ 4200 gallons of hot water per month,or 140 gallons per day. For a family of 4, 140gallons per day is not too bad, if you are single, it sucks.
Obvius things to check. Get a 5 gallon bucket and time how long it takes the shower to fill the bucket. You can get down to around 2 gpm shower head and still have a good shower. Bathroom sink aerators should be around 1 gpm. Kitchen sinks ballpark 2.5 gpm. Newer dishwashers use much less water then old ones, same with washing machines.

As far as costs go assume point of use electrical water heaters have 100% efficiency, tank type ones 80% (ballpark based on usage, standby losses, length of pipe in between heater and usage).
1 kwh = 3412 btu electricity ~0.17$ kwh here in CT
If you used electricity to generate the hot water, it would be 2,000,000/3412= 586 kwh/ month at 100 % efficiency or 100$ per month in hot water usage with tankless point of use, probably 125$/month with a electric water tank.
Oil uses 4,000,000 btu’s per month at 50% efficiency. 4,000,000 /138,000= 28 gallons per month *4.50$ gallon = 130$ per month.
Again, your best bang for the buck is probably an indirect tank from the boiler, configured the way Dana indicated, along with reducing hot water usage.
Oh and don’t read too much into the back of the envelope calcs I made above, we don’t have much information to go by.

Other questions?
How many gallons per year of oil do you use?
How many people living in the house?
How much electricity do you use per year, per month average, and in Jan, Sept, and July.

Cheers,
Eric


Think Energy CT, LLC Comprehensive Home Performance Energy Auditing
Dana1User is Offline
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05 Apr 2011 12:11 PM
I you use an indirect + heat-purging control you can set up the boiler for cold-starting rather than maintaining temp in the boiler all summer (or during the shoulder seasons.) Operated this way your summertime fuel use would drop by half or more. With the right control scheme you can safely repeatedly cold-start standard oil boilers without corrosive condensation when running an indirect because the coil of the indirect pre-heats the boiler using the thermal mass of the indirect, shortening the time period when it's operating below temp. (Some boilers of the 1990s were designed to be cold-start tolerant on their own, but when using the tankless coil you had to keep the boiler at temp anyway.)

You can run an electric tankless in series with the output of the indirect if you plan to simply turn off the boiler during the summer. When the incoming water temp at the electric tankless at or above it's setpoint the tankless uses no power, so when the indirect & boiler are operating the power used by the tankless would be nil. A 20KW tankless might be enough to run the shower and one other smaller load simultaneously during the summer, but probably not in winter with your incoming water temps. But the cost of the electric upgrades for installing a tankless might be a bit daunting- you're looking at a dedicated 100amp 240volt service drop for the just the tankless.

Without knowing your tank size there's no way to assess what your annual or summertime fuel use is, but with an indirect it would be cut in half. If you're the showering type (as opposed to a tub-bathing) family, installing a drainwater heat recovery system down stream of the main shower as pre-heat for both the cold-feed to the shower & water heater (whatever type you use.) It takes at least 4 feed of 4 inch, or 5 feet of 3 inch vertical drain pipe down stream of the shower to get ~50%+ return out of a drainwater heat recovery system. (Fatter & taller == higher return.) For showering families this is typically good for a 20-25% reduction in water heating fuel use. For a comparative list of models/by performance see: http://oee.nrcan.gc.ca/residential/personal/retrofit-homes/drain.cfm?attr=4

The US distributor for Power Pipe is EFI, who will set up an account and sell wholesale-direct in onesie twosies over the phone with a credit card: http://oee.nrcan.gc.ca/residential/personal/retrofit-homes/drain.cfm?attr=4

Note: Some local inspectors have an issue with the ASTM ratings of sub-components of PowerPipe (who uses a heavier stock for one part than falls under the more general potable water ASTM mark), so it might be a good idea to pre-approve the model with the locals before installing it at your house. Several states offer rebates for them, and have that vendor listed, but SFAIK not CT. (OR, MN, VT, WI etc.)

What are the input & DOE heating ratings of your existing boiler? Given the description of your house and the Waterbury location I'd expect your outside design temp to be in the +5-10F range, and design condition heat load to be on the order of 25-30KBTU/hour unless your infiltration rates are high. (DO have the place blower-door tested & IR imaged for fixing any gaps and you should be getting down there or even lower for short money.) Even the smallest oil burners are 2x oversized for the whole house load and MANY times that of your smallest zones. If yours is rated 100,000BTU or higher you're at least 3x oversized, and operating on the cliffy end of the curves in the regression plots of the appendicies of the Brookhaven boiler analysis: http://www.nora-oilheat.org/site20/uploads/FullReportBrookhavenEfficiencyTest.pdf

Heat purging controls such as the Intellicon would almost certainly reap double-digit savings on oil use during the heating season as well, especially since you have it multi-zoned.


whatAreMyOptionsUser is Offline
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05 Apr 2011 12:20 PM
Lots of information here, it's hard to know where to start. When I get home tonight, I'll try to get as much of the requested information as I can. I do know that my oil tank is less than 275 gallons. It's more like ~175 gallons. I don't know what the actual capacity is because it is sealed away under a plaster type structure and all that I can see is the oil gauge. Thanks for the replies, I chose the right forum for my questions. I'm not familiar with some of the terms you are using since I have almost no HVAC knowledge.


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05 Apr 2011 03:11 PM
Getting a gallons per year number and the boiler's BTU ratings are necessary for running FSA calculator tool.  If you know the model name/number we might be able to dig up the ratings from the web, but somewhere on the boiler there's a plate indicating it's input & output ratings that will say something like:

Input: 120,000BTU  (or it might be in MBH or gph)

Output: DOE heating capacity 103,000BTU  I/B/R water 93,000BTU

AFUE: 85%

or something similar.  It'll look something like this:

http://technivend.com/images/IM...5-0617.jpg


and may be on the outside, or inside a door/panel.

The FSA Calculator will also give you an estimated design heat load for weather if you use a gallons/year number and a location (Choose either Hartford or Bridgeport from their list.   On the equipment selection section choose "custom boiler", and use the numbers from the plate on the boiler.  The steady state efficiency to plug in will be output BTUs divided by input BTUs (in percent)

For yuks (and to remember the specifics of the tool) I ran one for 800 gallons/year of oil consumption for a house in Hartford, plugging in 86% efficiency with 100,000BTUs of heating capacity for the boiler, heating 64 gallons/day of domestic hot water.  The tool estimates that the design condition heat load (the coldest 1% of hours of the heating season) is ~25,500BTUs/hour, but the operating efficiency of the system is estimated to be 59% (due to the ~4x oversizing of the burner output to the amount of heat you actually need.) 

Dig through old billing or get the records from your fuel supplier, and using say 2-3 full years of use, figure out roughly how many gallons of oil you use in a year, then look up the numbers on the plate (or the model name & number) to figure out the rest.  If you have 3-4 people showering there every day 64 gallons of hot water use is the right ballpark, if it's 1-2 you might back that off to 45 gallons or lower to see how it affects the result.

If your boiler's specs are similiar (or higher) than the 100K output case I ran, you could see about a 25-30% reduction in annual fuel use by setting it up with a buffering reverse-indirect like a TurboMax or Ergomax, using a retrofit heat-purging controller on the boiler. If the boiler has only 60,000BTUs of heating capacity your efficiency jumps to ~68% (and the calculated heat load at design conditions is now recalculated to be ~30,000, if you used 800 gallons), in which case the fuel savings of a bufferd & heat-purge approach would be more on the order of 15-20%.  (IIRC 60,000 BTUs was about the smallest burner available for oil boilers in the '90s.  Smaller versions exist now, but not much smaller, and they often tend to have nozzle-clogging issues.)

The temp you'd have to set the reverse-indirect tank to depends on how much baseboard you have, etc, but odds are good you could run it at 130-140F year-round (set-it-and-forget-it), which is about where you'd want to set it for the summer.  But the configuration would look something like this schematically. http://www.ergomax.com/Radiant.jpg or this

I understand that you don't necessarily want to become a heating system designer, but you might have to be super-specific about your goals when dealing with the contractors/designers who reconfigure the system.  If you look at that Ergomax system schematic, note that the zone pumps draw exclusively from the reverse-indirect, and are completely independent of the boiler loop's pump.  The boiler's controls only "see" one zone- the buffer tank, and don't care whether it's one, three, or heat leaving via the tank's internal coil when somebody is showering that caused the tank to drop below it's setpoint, turning on the boiler.  If you use an Intellicon HW+  to sense the call for heat from the reverse-indirect, it "learns" the system, and turns off the burner on the boiler before turning off the boiler's pump to draw as much heat as it can from the hot boiler into the reverse-indirect.  If the boiler is thus "parked" at 130-140F at the end of each burn rather than 160-170F  it's standby losses are reduced dramatically.  Boilers are typically not well insulated, but indirects are, so the standby loss from the tank is much lower than the situation you'd have with a boiler maintained at 140F+ continuously (the summertime HW heating condition)  rather than parked at a lower temp at the end of a burn and allowed to cool off between burns.  The result is a net-boost to your as-operated system effiency, even if the boiler is way oversized for the amount of heat needed. 

If you needed 100% of the heat of an 86% efficient boiler 100% of the time you get 86% efficiency.  But with a 4x+ oversized boiler you never need more than 25% of it's output (except when showering, which is a tiny fraction of the time), and the average is less than 10% of it's output, which means it's spending the bulk of it's time in standby mode, and cycling on/off often with fixed-losses at every ignition cycle, which is what reduces it's efficiency to ~60%. By adding the reverse indirect you're reducing the number of cycles, since heat stored in the tank can be drawn even without involving the burner (and the thermal-mass of the tank is several times that of the boiler itself), and by using an Intellicon or Beckett control, you're cutting the boiler's standby losses by a large fraction.


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05 Apr 2011 03:36 PM
FWIW: A small ErgoMax (model E23 or E24) or TurboMax reverse-indirect runs about $1100-1500 f.o.b. the distributor's warehouse (see http://www.bgmsupply.com/searchresults.asp?category_id=156 for an example) , an Intellicon or Beckett controller is a couple hundred (eg: http://www.patriot-supply.com/products/showitem.cfm/155940 ). You may be on the hook for another pump, depending on how the current system is plumbed & controlled, but the existing zones can probably use the existing controller with some minor wiring changes. The installation cost will vary depending on just how much space there is and how awkward it is, etc. but if you presented the "plan" to a few different heating & plumbing contractors and get quotes from those who seem to understand the concept without too much prompting on your part you should be able to get something reasonable installed for under $4K (maybe under $3K) if there's any competition in your market. The key might be find somebody who has experience designing & installing both reverse-indirects and economizer controlls. (You might find out from the manufacturer or distributor which contractors in your area have been buying their reverse-indirect HW heaters.)

A decent heating contractor would be able to tell you based on the heat-load number calculated by the FSA tool based on your fuel use with the existing system whether you have enough baseboard to deliver the heat at 130F or not. Even if they think it's a higher number, it doesn't hurt to turn it down to 140F, and only bump it 5F at a time if it doesn't stay warm enough on the very-cold days. The min-temp programmed into the Intellicon should be about 140F no matter what tank temp is set to, unless the boiler is a "cold start" type (which would be described in the manuals & literature for the boiler), but the installer/contractor should be able to explain that to you (rather than you explaining it to them.)


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05 Apr 2011 09:09 PM
Unfortunately I can't get exact gallon amounts for the previous years until tomorrow when the oil supplier is open. I actually switched oil providers a year and a half after moving in so I only have 2 years of history that I can verify. This also means I can't use the calculator from Dana1's post until I can get the gallons I used, otherwise the calculator input values will be more guesswork than anything. I can only get payment histories back to April '09 from my bank website. I do know I spent $1753 on oil in 2010. That doesn't sound too bad, until I look at how much I've already spent in the first three months of 2011- $1380! And come May 1st, I will probably need another fill-up to the tune of $500-600.

Here is the information from my oil boiler:

Model: Columbia Emerald Series EM-100
Input BTU/Hr: 140000
DOE Capacity BTU/Hr: 11300 (~80% efficiency)
Net Rating BTU/Hr: 98000
Burner Type: Beckett
Burner Model: AFG

BTW, I've got the heating audit scheduled for next week!


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05 Apr 2011 10:23 PM
10k might go a long way to cutting your consumption of fuel oil with an insulation company.
Geo is not going to get done for you with standard baseboards.
Start with envelope improvements, then ask local geo guys if they can make the numbers work for you.
j


Joe Hardin www.amicontracting.com We Dig Comfort! www.doityourselfgeothermal.com Dig Your Own Comfort!
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06 Apr 2011 11:05 AM
Well I got my past two years of oil usage today and tried using those values in the FSA Calculator. It doesn't appear to work correctly based on my oil consumption. See the attached screenshot. Any suggestions? [edit]The image attachment system on here is a joke. Here is a link to the uncompressed image: http://i.imgur.com/8azAy.png

Attachment: currentBoiler.gif

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06 Apr 2011 05:48 PM
It's a buggy tool which sometimes need a re-start to clear things when you enter erroneous data.

It looks like you plugged in 70 o 78 for the steady state efficiency, which should be 81% (113k/140k), if your reading the rating plate is correct, or 84% otherwise. According to the literature the EM-100 has and output of 118K (not 113) an AFUE of 83, which means steady-state would be ~84% see:

http://columbiaboiler.com/residential/emerald/documents/EmeraldSeriesManual10.08.pdf

http://columbiaboiler.com/residential/emerald/documents/emerald_brochure.pdf

You seem to have used an idle loss of 4.1% which is probably high. For a post-1980 boiler- try something between 1 & 3.

Is the fuel use 640, 540, 580 or ??? (the .gif is pretty blocky and hard to tell exactly what was entered)

I know you say you're not fully heating each zone, but plugging in 640 gallons/year, then selecting "custom boiler", and editing in 84% steady state, idle loss of 3% it's coming up with a design condition heat load of ~ 14.3K (which seems too low), but plugging or if 2% it's ~ 18.5K which is still low, but not impossible if you're only heating part of the house to full temp and using setback thermostats, etc. Plugging in 1% idle loss it calculates ~20.2K, for a heat load, which is starting to feel credible based on experience assuming 1/3 of the house isn't being heated fully. It's probably somewhere in that ballpark between 1& 2. Let's call it 1.5 (still just a WAG.)

Using lower fuel usage numbers the calculated heat loss is even lower, implying either a very tight house with a very low amount of window area, or perhaps an additional heat source, or you're keeping the place at 50F or something. Do you supplement heat with any other source, like a woodstove or electric space heaters or ???

But it looks like with any of the numbers you're operating below 60%, and possibly below 50%, and configuring the system with a reverse-indirect as a system buffer (and configuring the boiler controls for cold-starting with an Intellicon HW+ in the control loop) would make a huge improvement in average efficiency- well into double-digits. The only time you ever need the full 118K of burner output is if you were taking an hour long shower in the dead of winter, but it would still keep up at your house, with a 26 gallon ErgoMax E23 set to 140F. You may have to set it a bit higher if your baseboard is truly minimal in length, but I doubt it.

The boiler has 13.5 gallons of water, the ErgoMax has 26, so you're about tripling the thermal mass of the system from a minimum burn length point of view. With the embedded coil set up per manufacturer's instructions it looks like the boiler stays at 160-180F(!) as recommended by the installation manual in that first .pdf- (see section C on page 4.) You're basically changing the operating mode to that of a non-tankless version and inserting the smart controls for the low-limit & circulator control. The standby loss of a boiler that hot is higher than need be, and with that much burner and your low heating loads you could easily tweak the low-limit on the existing setup down to 140-145F, keeping the high limit at 180F (to keep the min-burn rate in stand by reasonably long), and reap at least a 5% reduction in fuel use since it cuts the number of burn cycles about in half, and reduced the average operating temperature by ~10F.

Set up as per the manual in tankless mode the minimum burn time in summertime standby is only about 75-90 seconds, and the first 6-10 seconds are a fuel-lossy ignition cycle- you've blown something like 6-8% of the totalfuel for that burn even before the burner is fully up snuff which reduces the average efficiency. But by doubling the difference between high & low limits the burns are twice as long, and the time between burns is long is a bit longer than twice as long- long enough that standby-only burns may (mostly) go away, so you've cut that fixed loss per burn by more than half.

With an ErgoMax reverse-indirect buffering the system they WILL go away, despite only a ~7F high/low difference in it's aquastat, the standby loss at 140-145F would be about a half-degree per hour. Then the only time the burner kicks on in summer would be during/after some actual hot water use, and with the smart controls installed would park the boiler near the indirect's setpoint at the beginning of standby, some 30-40F below where it's currently left at the end of a burn. That 30-40F difference in beginning standby temp represents the heat of over a half-cup of oil-burn that was most likely to have been completely wasted in a summertime burn cycle, now safely stored inside an insulated tank rather than a (much lossier) boiler. A cup or two per day of wasted fuel adds up over the course of a summer. The rate of heat loss of the boiler into a 70F room going from 140F to 100F is substantially longer than from 180F to 140F, despite it being the same amount of temperature drop, so even though the boiler has to burn a bit longer to come back up to temp on a cold-start the total system standby loss has been cut by about half, raising the summertime efficiency from ~25% to ~50%.

The annual AFUE of such a system can be estimated using the FSA calculator by selecting "Purge Control 88% AFUE..." from the boiler pull down, and editing the efficiency down to 84%, and the idle loss first up to 1.5%, let it calculate, and re-adjust the heat load guess, then bump the idle loss down to 0.3 or 0.5. It looks like you'd be going from a 55-60% AFUE to a 70% or more- an minimum fuel savings would be ~15%, but 25% would be still in the realm of reality.

If you have the exact dates between two fill-ups this season we can look up the heating-degree data between those dates and calculate a K-factor (degree days/gallons) which might get us a bit closer to your actual heat load. eg: Say you filled up on 26 January, then again on 17 March, and the March fill was 178 gallons, and the http://www.degreedays.net/ daily tally between those dates adds up to 1187, the K-factor would be 1187/178=6.7 Using K-factor rather than a wild guess on annual fuel use you'd have to either round up to 7 or down to 6- the tool won't accept fractional-K, but it's probably more likely to deliver a realistic heat load and other numbers than the above analysis.


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06 Apr 2011 09:31 PM
The EM-100 is a model they still sell, but the specs they list at the site do not exactly match what is on my boiler. I'm guessing they've made efficiency improvements over the last 17 years. As for your questions- 1.) I used 580 gallons for the calculator which is the higher of the past two years' oil consumption. The rest of the values I let the utility autofill based on the boiler I selected. Even with making the changes you recommended to the idle loss value, the program still warns me that the design day heat value is unusually low. 2.) I turned off the basement zone since even in the coldest months it never gets below 62F. 3.) I know there are "leaks" in my house as I can feel a slight draft coming from upstairs on cold days. So I know I can do much better with sealing/insulation. 4.) Do you have a link for reading up on the differences between an indirect vs. reverse-indirect system? I've got someone coming by to offer a quote on adding an indirect tank and he didn't really have any answers for me when I mentioned a reverse-indirect system. He did mention that with an indirect tank that the boiler would now have be able to run from a cold start instead of having to maintain the 140-180f temps that it does now. My current aquastat will be going away with this new system. 5.) I do have dates and exact amounts of the three fill-ups I've had since last fall. I did have the third zone running up until the end of January, so that is why my first fill-up of the year was so high. Nov-17: 140 gallons, Jan-17: 194 gallons, Mar-04: 160 gallons By the way, how the hell do you break your replies into paragraphs on this forum? Every time I post, it puts everything into one long rambling paragraph!


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06 Apr 2011 09:51 PM
By the way, how the hell do you break your replies into paragraphs on this forum? Every time I post, it puts everything into one long rambling paragraph!


And you would be posting from a Mac??


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07 Apr 2011 11:26 AM
No, Windows, but I am using Google Chrome. If I try to edit my post, the proper formatting is intact on that screen, it just doesn't carry over to when the post is submitted.


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07 Apr 2011 01:38 PM
You need to put < b r > (without spaces) where you want a break.

I'd consider a heat pump water heater for use in the summer. There may be other optimizations if you have offpeak electricity rates.


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07 Apr 2011 04:53 PM
The differences between reverse-indirect/indirect are a hydronic design problem related to output rates of your heating zones relative to the boiler output and the total mass of the zone+ boiler.  It really about buffered compared to unbuffered heating system (not reverse-indirect compared to indirect hot water) when the smaller zones aren't big enough deliver more than ~25% of the boiler's full output.  When that happens the boiler cycles way too often, giving up way much of it's fuel to ignition cycles and even more heat as standby loss.

Given that your whole-house heat load is but a fraction of the boiler's output to begin with, and you've chopped it up into even smaller zones, I'd be surprised if the heat load of smallest zone was even 10% of the boiler's continuous output, which means you either have to crank the temp up (so that the baseboards deliver heat at a faster rate) losing efficiency to distribution & standby, or let it short-cycle itself to low-efficiency on ignition cycles- it's a no-win situation.

The SOLUTION is to add thermal mass to the system in the form of an insulated tank, and let that thermal mass be involved in every burn cycle, stretching out the burns.  A reverse-indirect provides that mass, and that allows the baseboard to run it at lower temps without short-cycling, and which reduces heat loss from heating distribution plumbing, and further,  sets up the boiler run the fewest burn cycles possible, since it has only ONE zone to serve (the reverse-indirect), and isn't successively called by different zones or hot-water calls.  The burner only kicks on when the tank temp drops (either from the zones drawing water, or DHW coil inside the tank pulling heat out.)    This is a bit academic, and written from a larger-facility systems point of view but the math & concepts are identical to a multi-zoned residential application- see if you can't get your head around this: 

http://harscopk.qa.jplhosting.net/u...d0ef7d.pdf

Most residential installers haven't a clue about reverse-indirect or how to properly size a buffer tank, etc (or even how to do an accurate heat-loss calculation for sizing a boiler), and have relied on the mass of the boiler to be sufficient for running low-mass baseboard without unduly increasing cycling losses, and break it up into zones with no regard to what that does to cycling losses, boiler wear, system efficiency, etc,  but given the present and anticipated cost fuel, continuing to install such low-efficiency systems is a almost a CRIME.

Your boiler was probably sized to be able to run some overestimate of heat load AND a 5gallon per minute tub fill simultaneously.  Going with a standard indirect would be more beneficial if the boiler's output was too small to serve the hot-water draws with a continuous burn, and was at most 1.5x oversized for the peak space heating load.  But with the 113K output of this boiler you could run a standard 2.5gpm shower literally all day long without the need for a storage tank, so an indirect run as a separate zone isn't buying you too much in that regard.  (And standard controls for an indirect doesn't heat-purge the boiler into the indirect, so it would abandon heat in the boiler.) Even though it's more money and more work, re-plumbing the heating system with a reverse-indirect as the point of hydraulic separation in a primary/secondary archictecture, with the boiler-loop slaved to the aquasat on the reverse-indirect, and using a heat-purging control at the boiler buys you a LOT more in efficiency.

CT has some of the most expensive electricity rates in the lower 48.  If you can boost the summertime efficiency of the boiler to 45-50% it'll probably be cheaper to continue to run than using an electric tank (even an expensive heat-pump hybrid type) or on-demand tankless, and the capital cost for something extra just for that 3-4 months/year of savings would be somewhat wasted even if it did end up with a somewhat lower operating cost for that period.


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08 Apr 2011 04:03 PM
I think I understand the distinction with a reverse indirect. Mainly that all three heating zones and DHW are pooled from the separate water tank instead of the limited amount of hot water in my boiler. The heat capacity of the water in the tank is a better buffer against temperature fluctuations from water use and/or zone heating than the small amount of 140-180 degree water in my current boiler. In a standard indirect water heating system, the tank is simply another zone in addition to the three I already have. The first contractor I spoke with about reverse-indirect pretty much dismissed it, it's certainly an interesting concept. I've got two quotes lined up, but it looks like I'm going to need to do a lot more blind calling to find someone who knows about indirect and reverse indirect and is willing to offer quotes on both. I've learned more in the past week about this stuff than I've learned in the three years I've owned the home!

How much retooling of the heating zone and DHW plumbing are we talking about with a reverse-indirect system? Shouldn't any changes that need to be made happen only at the piping around the boiler?

[edit]Well I just received my first tentative quote. He gave me a rough estimate of around $10k for a new boiler and indirect tank. I didn't mention how much I budgeted for this. He uses Buderus brand boilers and tanks. Specifically, he mentioned this line: http://www.buderus.us/products/oilheating/oilconventional/logano-g125be.html

He said he would quote the 96k BTU model, but I thought I might be able to get by on the 72K BTU version. I'm impressed by this brand's efficiency ratings and the fact that it has the outdoor temperature modulator built-in. Anyone have thoughts on this? I'll post back when I get final numbers on the quote.


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09 Apr 2011 11:37 AM
It reads like you've grasped the difference between indirects and reverse-indirects, and why one might be preferable over the other based on the boiler size relative to the space-heating requirements.

Installing a reverse-indirect & heat purge controls should be relatively straightforward if you have enough room next to the existing boiler,  since your hot water and heating zone plumbing is already concentrated there.  Depending on how the existing system is pumped you may have to buy a another pump for the boiler-loop, but except for cutting in to the burner controls, the same zone controllers and pumps could probably stay.

$10K is the right order of magnitude if you're going with an all-new high-end boiler like a Buderus G125 + indirect, (a bit on the high side for a smallest-in-the-line boiler though, which is what you should be looking at- I have NO doubt that your design heat load is well under the 73KBTU/hr output of the smallest G125)  but unless your existing boiler is ready to die, re-commissioning it with a buffering indirect would be half the money, and would deliver much better efficiency than you've been running.  The smallest Buderus 125 is still more than 2x oversized for the load, and no matter what it has for an efficiency rating, as-operated in your house with your low space-heating loads it won't hit very close to those numbers without buffering. The smallest Buderous G125 series will perform similar to system # 5 in that Brookhaven Nat'l Lab study, whereas your existing boiler set up for cold start +  Intellicon/Beckett purge control + reverse-indirect would run about 6% lower efficiency than system #3 (due to its  lower steady-state efficiency than system #3). 

Look at Table 3, and consider the annual efficiency for system #5 at the 2x oversizing numbers vs. #3 (less 6%) at the 3x oversizing  for the best rough-comparison. You'll find that while #5 is  better, it's only ~4% better.  Your as-used efficency on the existing boiler as currently operated is probably similar to system #2 with 3x oversizing, or best-case, 3% less than system #1's  3x oversizing numbers.

Best bang-for buck, you're likely to be better off spending 3-5 grand on tightening up the place and adding spot-insulation where appropriate/easy, then recommissioning the existing boiler with a buffering reverse indirect & heat-purging controls.  In 10-20 years when the boiler has really had-it, a reverse-indirect should still have decades of life left in it and about any boiler could be swapped into the boiler loop with minor changes.  The costs of weatherizing an air leaky house are modest (and often subsidized by both state & federal governments).   It's pretty common to see 15-20% reductions in heating fuel use just with a solid round of air-sealing (more, for really old places with leaky double-hung windows and sagging wall-cavity insulation.)  Report back what the air-leakage numbers are from the blower-door test.



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