I am replacing my 40 gal. natural gas hot water heater (standard venting) and I was wondering if there are any recommended brands/models: State, GSW (owned by A.O. Smith), Bradford-White, or other? I would like a high quality energy efficient model with good insulation. Are these features worth it? - magnesium anode or aluminum anode rod? - self-cleaning system? - glass lined tank? Thanks.

Direct-vented power drafted versions have efficiencies beyond what shows up in an EF test, since they're not drafting conditioned air out of the space 24/365 the way atmospheric-drafted versions do. (You only need/want the flue to draft for combustion exhaust when the burner is active, a ~1% duty-cycle instead of 100% duty cycle.) Start there.

Have you considered switching to a "On demand" tankless hot water heater. They will save money on your gas bills and also free up some much needed space in your mechanical room.

Just a thought to consider.

As a replacement for a tank it's rarely just a drop-in to go with an on-demand, since the BTU input requirements are typically more than 5x higher, and the venting requirements are different, often with special materials required.  Power vented tanks are a lot easier to deal with as a retrofit as a tankless, and in most installations the difference in as-used efficiencies won't be enough to ever make up the installed difference difference in fuel savings.

There are exceptions of course.  If your absolute flow requirements aren't huge and your incoming water is usually above 50F, it's often possible to swap in a ~100-125KBTU atmospheric drafted on-demand with flow-powered magneto ignition like the Bosch 1600H for lower installed cost and higher efficiency than a forced draft tank. At ~81-82% combustion efficiency (0.80EF) you can use cheap B-vent and vent it into a chimney, and since it has flow-powered ignition you don't need to run electrical service to it.  It's only a couple percent under the efficiency of bigger-deal on-demands, but the installed cost will be far lower.  That particular model may have issues with flame-out at extremely low flow since it's lowest modulation is ~28KBTU (under 20 is easier to deal with), but it's pretty easy to get used to. I lived for 15+ years with a similar sized unit in central MA- it's wasn't terrible, but you couldn't run the laundry and take a shower at the same time in mid-winter (but in the late summer you could.) 

Depending on the length of the run, you may still need to upgrade the gas lines even for a 125KBTU unit though. (Over 150K, the gas lines have to be pretty fat.  If you have other big burners in the house you may need to upgrade the meter, or in extreme cases, the service from the street.)

If your goal is to save fuel, the $1000 difference in installed cost might be better spend on drainwater heat recovery and insulating all of the distribution lines. (No matter how you're heating hot water, insulating the plumbing to at least R2 everywhere.  With tanks, put minimum R4 on every pipe withing 6' of the tank to cut down on standby loss. This includes the cold water feed and the pressure/temperature valve outlet.)  In frost-free zones, applying the difference to batch solar pre-heat is a better investment.

There are lots of reasons to go with tankless, but fuel savings alone can rarely rationalize it. The most common reason is the capacity to fill large tubs or take endless showers without running out of hot water. Space savings is #2. Efficiency is somewhere down there around # 4-5.  The difference in efficiency isn't nearly as much as the EF numbers imply, since EF tests take draws 10.2 gallons at time. For a 1-2 quart short-cycle even a 0.95EF condensing tankless will barely make 60% efficiency, and then only if it's already warm (the last draw was less than 5 minutes ago). Cold, it won't make 50%. But by the time it hits 5 gallons or so in a single draw it'll begin to approach it's steady-state potential.

But if you have a hydronic (forced hot water) heating system, the greenest-cleanest and still pretty cheap solution is to install an indirect-fired tank on the heating system (either as a seperate zone, or a "reverse-indirect" as a heating system buffer, whichever is most appropriate for overall system efficiency).  It's more than a cheapo standalone tank, but it'll be cheaper than an on-demand, deliver as-much or more water as an on-demand, with higher flow and none of the tankless quirks like the 'coldwater sandwich' and temperature regulation/flameout issues at low flow.

I had considered this but decided against it for the reasons that Dana1 has explained
Actually, I do have a hydronic heating system but what I am struggling with a few things regarding the replacement of my current furnace with a combination furnace providing both space and water heating:
- isn't it overkill (and perhaps inefficient) to have this big furnace just heating water in the summer and the off-heating season months?
- how does it alleviate the "coldwater" sandwich problem?
- it seems awfully expensive

Can you tell me where I might get more information on this option and good brand name products to check out?

Currently both my water heater and gas furnace vent up the chimney. Is it worth it to change this as well, with a power vent for example?

Thanks.

Water heating efficiencies in the summer with a big-fat boiler and and indirect (as opposed to an internal heating coil on the boiler) are similar to atmospheric-drafted hot water tanks- not much better or worse.  But during the heating season it improves the efficiency in both modes by increasing the duty-cycle (and with the right controls) minimum burn lengths.  See:

http://www.nora-oilheat.org/site20/uploads/FullReportBrookhavenEfficiencyTest.pdf

(note: "tankless" in the above document refers to an internal heat exchange coil in the boiler, not an on-demand hot water heater.)

The "coldwater sandwich" effect its a tankless thing- the flue-purge cycle actively takes heat out of the heat exchanger, and the delay in ignition allows some cold water to pass through the tankless essentially un-heated. An indirect tank has the whole thermal mass of the tank, and it's drawing off the top where the hottest water is- always.

Standby losses on indirects are quite low, since they are fully insulated, with no center-flue heat exchanger to convect/extract heat of the tank at idle.

A reverse-indirect adds mass to the heating system and guarantees longer burn times without special controls. During the heating season, a single aquastat set to the temperature needed by the heating system works fine. During the summer, setting it back to the minimum input-water temp allowed by the boiler is fine (typically 140F for oil- fired systems, but 130F can usually work for gas boilers as long as it has a condensation-tolerant flue.)  If the boiler is WAY oversized a dual high/low limit set of controls can be set up to allow for longer burns in hot-water-only heating.

If you go with a power-vented tank,  or a high-efficiency boiler (or high efficiency furnace) side-venting is preferable, often mandatory (unless you feel like buying a stainless steel liner for the chimney.)  Condensing heating appliances and most power-vented tanks can even use PVC for venting, but not as a liner within an existing flue.

The peak BTU/hr rates for hot water use are often several times that of the heating load (except in the coldest parts of the lower 48),  but they're intermittent, so buffering the load with the water-mass of the tank allows the burner to run long enough to hit steady-state efficiency, even in the summer. Low mass burners like condensing boilers or hot air furnaces have very low standby loss compared to the high-mass boilers studied in the Brookhaven study, above, and will perform considerably better during the summer season than those cited.  A tankless hot water heater is also very low mass, but with small volume draws the heat wasted is nearly what was used, and they only gain it back with higher volume draws of 3++ gallons/per draw (10-20gallon per is even better, for efficiency but not necessarily the fuel bill. :-) ). They're great for showers & tub draws- lousy for water-sipping high-efficiency washers & dishwashers, or hand-washing draws. The average efficiencies tend to be 8-10% lower than their EF numbers might indicate (since EF test draws are about 10 gallons/per.)

I abandoned my chimney-vented cast-iron boiler & modest-efficiency tankless sharing the same flue for a side-vented sealed combustion tankless (Takagi T-KD20) and a reverse indirect tank over the summer. I'm still dialing it in (some of the radiant zones aren't yet installed), so actual efficiency is still TBD, but early indications are pretty good.

Manufacturers of reverse-indirect/buffers most accessible to the US market (that I'm aware of) are TurboMax, Everhot (EA series only), and ErgoMax.  You may have to call them to find the nearest distributor, but they're commonly used in commercial applications (multi-unit apartments, etc.), and there is likely one available at distributor near you.  A 25-35 gallon reverse indirect should be half the installed-cost of a tankless on-demand if the heating system plumbing is simple & accessible.  A crude schematic of a heating system using one looks like this:



Details of what works for you (or me) can and will differ, but it basically makes the tank the point of hydraulic separation in a primary/secondary loop configuration, and the DHW is basically passive. The boiler only kicks on when the tank calls for heat, and the heating system zones only operate circulators- the boiler is completely agnostic about the state of zone-calls, slaved only to the tank's temperature controls.

Whether anything like this makes sense at your place depends a lot on the particulars. (You say you have a hydronic system, but you also talk about a "furnace", which usually refers to a forced hot-air system with air handler, ducts, & registers,  not pumps, pipes, & radiators/baseboards.)

Thank you Dana1 for your comprehensive response.

You really have me thinking now in another direction. I have looked at the reports you cited as well as the reverse-indirect units you mentioned and I now understand this technology much better. It all looks very interesting and makes a lot of sense.

So naturally I have some more questions:

1. If I install a reverse-indirect unit, can I still use my existing gas boiler? My boiler is a HydroTherm C-125E that is 13 years old (125K BTUH)
2. Among the reverse-indirect units you mentioned, TurboMax is near my area (Montreal) so I would tend to go with it. Any significant differences with Ergomax?
3. My current 40 gal. gas water heater is adequate for our family needs, so would a 26 gal reverse-indirect unit would suffice, since it is heated on demand anyway? How do I size it properly?
4. Should I replace my current boiler with a high efficiency gas boiler? (any suggestions on makes, models?)
5. If I do, then I guess I could plug up my chimney flue and vent directly outside. Could I also get a direct air intake from outside to reduce cold air infiltration in the heating room? (Currently, I have a intake duct that draws in air from outside as required but is always open; it would be nice to have an intake that would open only when air is required for combustion)
6. How much would a new high efficiency gas boiler set me back?

Thanks again.

1. Yes, you can use your existing boiler.

2. TurboMax specs are nearly identical to Ergomax specs in similar-sized units. (TurboMax have a much more finished LOOK though.)  I have no direct experience with them, but their reputation is good.

3.  Your 40 gallon tank had only a ~35K burner on it, whereas your boiler has a 125K burner.  Your 40 gallon tank probably had a storage temperature limited to 140F/60C, and you could (if needed) crank up the temp on the indirect for more capacity. (DO put a tempering valve on the output if you're keeping it above 130F/55C, which you'll probably need to during the heating season.) Without looking up the specs on your boiler, assuming it's at least 80% efficient, it'll deliver a net 100KBTU/h into the tank. 

Look at the first-hour specs on the various models, under the net-100K rows:  http://www.thermo2000.com/pdf/en-US/specs/turbomax.pdf  

Any one of the smaller ones will deliver ~200 first-hour gallons at 110F (a hot-hot shower, or medium hot bath), or ~130 first-hour gallons of 140F/60C water (DANGEROUSLY HOT WATER, but probably the minimum temp you should set the tank in order to protect the cast iron boiler from too-cool return water.)  By contrast, a typical 40 gallon tank delivers 70-90 first hour gallons.   Mind you, when it's -25 outside and the heating system is running full-out you may only get 100 first-hour gallons out of it, but assuming your design day heat load is under 70KBTU/H you'll still beat the 40 gallon tank during the very coldest hours of the season.)  With 100K input you can run a 3.3gpm shower all day long, if that's the only load. The difference between the two 26 gallon TurboMax units isn't first-hour gallons, but heat exchanger surface area. With the bigger heat exchanger you'd be able to pull hot water out of it at a higher flow rate, but unless you intend to run more than 2 shower flows at a time out of it you may not notice a difference.  You'd be burner-limited for continuous flows that high anyway, but you could run 2 showers simultaneously for 10-12minutes before it fell behind enough to notice. If you had a 250K boiler behind it you could run 2 high-flow showers all day long. (Any indirect is only as "big" as the burner behind it, but yours isn't a wimpy burner by any means- you won't have to upsize the tank volume  for DHW reasons.)

Also, the ratings are based on 180F boiler output water, and 40F incoming potable water.  It's probably worthwhile to set it up to have the boiler loop pumping before the boiler output itself hits 180F (145 or 150F would be fine for a gas-fired boiler, with 130F storage temp on the tank), which will give it slower ramp at the beginning of a burn, but you'll still have hot water.  No matter how small you go, you'd really have to work at it to run out of hot water, and if you did, you could turn down the room thermostats and wait 5-10 minutes for it to come back up to temp.  100KBTU/h is enough to run a high-flow shower continously with 40F incoming water. But if you're filling a huge 50 gallon tub you'll have to slow the flow to ~3-4gpm by the end if you go too small. (Standard sized tubs can usually fill at full flow with a 26gallon indirect. You can bump up the storage temp and get a bit more out of it if it doesn't quite make it.)  If your 40 gallon standalone is adequate for your needs, a 26 gallon indirect should be.


4. It's usually only worth replacing a functioning boiler if it's grotequely oversized (it's output is 5x your heat load) or is extremely old & inefficient, or the price of fuel looks like it will be extremely high for the next decade.  A 13 year old boiler in good shape could easily go another 20-25 years.  When it hits the ripe old age of 20 or it needs an extensive repairs, then think more seriously about replacing it even if it's still functional (or could be for $1000 of work.)

5.  There are automatic combustion-air dampers (similar to forced-hot-air zone dampers) that can be interlocked to the ignition in much the same way as the automatic flue dampers.

6.  Modulating condensing boilers in the 100K range start at about $3KUSD for just the hardware. With all of the other usual work & hardware required for an installation you're looking at between double & triple that by the time you fire it up. It's sometimes more, but I've yet to see a mod-con boiler installation come in at under $7KUSD in my neighborhood, some are over $10K.  Assume you'll get ~80% efficiency out of your existing boiler, and (unless you have low-temp radiation on your heating system) ~90% out of a mod-con.  Whatever your annual fuel bill is, with the new boiler it'll be ~ 8/9 of what it is, maybe a little less if your true design-day heat load is under 50K, making the existing boiler 2x oversized.  Will the fuel savings pay for the new boiler in any reasonable time frame, even if the installed cost is as low as $5K?  (Usually not...  but if the price of natural gas quadruples it might.)

With a cast-iron boiler your summertime fuel bills might be ~10% higher than with a standard tank, but if your wintertime fuel bills are 10% LOWER, it more than makes up for it.  Annually you should expect to see real savings, but unless you track your fuel use against heating degree-day data, it might not be obvious.  Any decent indirect should last decades though, and using it with any replacement boiler down the line shouldn't be a problem.

For a more detailed explanation of how & why a reverse-indirect boosts the efficiency of the heating system, read this:

http://www.patkelco.com/uploads/files/4bf77cff8bc8411bb00c67e962d0ef7d.pdf

It's written from a large-facility point of view, but it works on the micro-scale too. The more zones you have set up in your house, the bigger difference buffering it with a reverse-indirect will make, but even in a single-zoned home and perfectly sized boiler it'll be a measurable improvement, since 98% of the time the boiler isn't running at 100% duty cycles. 

It's a significant chunk of change up front compared to a standard hot water heater, but it'll last forever, and it'll likely pay back the cost difference in under 5 years if natural gas picks up to pre-recession price levels.

Wow, thank you for this very detailed response! You have pretty well answered all my questions and your answers jive with what I also found out today talking to some plumbing contractors and an expert at the gas company.

Concerning the article you mentioned, I had already ready it (found it in these forums in another one of your posts).  I am definite sold on reverse indirect (thank you for the lead) and have spoken to Thermo2000 (Turbomax) today. Was not too impressed with the guy we spoke to there as he advised their "34" model, which is 36 gal and 4 coils. That is oversized for our needs. The "23" model (26 gals and 3 coils) has identical output for 100,000 BTU, both for first hour and continuous. In fact continuous is 121 gal/hr which is more than adequate for us. We will not be taking simultaneous showers, do not have a hot tub and our appliances are energy and water efficient.

He priced the "34" model at C$2000, which sounds pricey, but I am hoping the "23" is more like C$1200. And then there is installation...

As you stated, I also confirmed that I can use my existing gas boiler (which is great since it is only 13 years only). The gas company also advised us to keep it and said it had a useful life of at least 25-30 years. It does run at about 80-84% efficiency. One thing that is great about our boiler is that is does not need electricity to run, so we have heat even during power failures. (also hot water)

Next step, get some quotes....

Dana1, if you come to Montreal, I owe you a few beers!

The smaller units should be under C$1500, even the "24". If not, a siimilar-sized ErgoMax will be, even with shipping:

http://www.bgmsupply.com/searchresults.asp?category_id=156

The Everhot EA 8-50 is a 30 gallon with about the same sized heat exchanger, so it should be similar money. They're located in the Boston area, so shipped direct shouldn't be very expensive either.

In order to use a reverse-indirect as a buffer you'll need electricity to run circulation pump s to stay in heat & hot water. The boiler's internal controls will keep it from overheating, but if you re-configure the system to make it tank-centric, with the boiler only slaved to the tank it'll need electricity.

Are you saying that your current radiation runs completely on convection? I've seen this in 100 year old houses- the pipes are quite large in diameter and the water mass in the system many times that of a reverse-indirect, in which case an additional 25-30 gallons won't make much of a change in efficiency.

I have not heard back from Thermo2000 concerning the price of the smaller Turbomax unit but did speak with a plumbing contractor who said the installation costs would be about $4000! I find that very hard to swallow. I understand the the pipes need to be rearranged to accommodate the reverse-indirect system and the proper controls need to be installed, but $4000?? He said an indirect system would cost 1/4 of that (i.e. $1000) to install. Why would that be? In both cases, the pipes need to be arranged and you need the controls. I will get other quotes but this was certainly discouraging news.

Our house is not complicated. The boiler was only installed 13 years ago, with a new pipe set-up,  there is adequate space to work and there is only ONE heating zone. There is an electric circulation pump that circulate the water through the house but if there is a power failure the boiler can continue to function and the water (slowly) circulates through the system by gravity. It is slow but it keeps the house perfectly warm. We went 11 days without power in the 1998 ice strom and we had heat and hot water all the time. Our pipes are 1-1/2" in diameter.

Calling all plumbers/installers in Montreal that know these systems and have reasonable rates.

To be continued...

$4000 seems quite steep. Keep shopping around.

All the plumbers are now off for the holidays so I have to wait until early January to get more quotes. I will let you know how the journey progresses.

First post,

We just moved here from England, where we had a combined condensing boiler for the last 7 years, we have been very pleased with it, it is small, very efficient and not expensive $1200 (http://www.cheapboilers.com/gas/combi/glowworm/30-cxi.htm but there are many different brands).

Our "new" house just outside New York city,  has

boiler: Dunkirk PWB-7D 210.000 BTU 81% efficient, from 1992,
hot water: Bradford White Defender 50 Gal 40.000 BTU, from 2007,

I really would like to get rid of the chimney, so my initial plan was to just install a combined condensing boiler, but I cannot find one here, at least not the inexpensive small (size) wall-hung units like the ones we have in Europe.  I would also like to reduce my CO2 foot-print, even if it is not completely free, but otherwise I am the cheap kind.

Then I red dana1's description of the "reverse indirect tank",  and especially the idea of using a Takagi T-KD20 as the power source
(if I understand correctly), got me Thinking.   How about the control system, is it enough just start and stop the pump when the temperature drops in the storage tank or does require something a little more sophisticated.

I have always done the plumbing myself (except gas due to regulations), Are you allowed to do taht here in New York state

Best Regards

Peter Lorenzen

My boiler loop through the Takagi is controlled by solely by the aquastat on the reverse-indirect operating a relay for the circulation pump. It has about 4C of hysteresis built in. If more is needed/desired one could get a bit more complicated with dual aquastats for high/low limits.  The heating system zone thermostats control circulation pumps to the radiation. (I investigated using an ECM motor pump and zone valves, but that proved a bit pricey compared to multiple smaller pumps, even though it would have used half the electricity.)

Small condensing boilers here start at ~$3KUSD, and I'd be using one myself were they were half that.  My peak heating load is only ~9KW, but for water heating un-buffered(no tank) I'd need something closer to 30kw.

I'd be surprised if the peak heat load on the average house near NYC was even half the output of that Dunkirk, in which case it's actual as-used average efficiency is likely to be closer to 70% than the 81% on the name plate.  Putting a reverse indirect-buffer on it would raise it to over 75%.

If the your peak heating load is in fact over 85kbtu/h (25kw) the Freewatt Hydronic cogenerator system (see:  http://www.freewatt.com/products.asp?id=172&name=Hyd ) is likely to be a very good investment, given NY utility pricing, and would reduce your CO2 footprint far more than a mere high-efficiency heating system.

Dana1, Thank you so much for your answer

I have tried to get a to know our house and its heating system a little better (we have lived her 6 weeks). To do that I have made a little data-logger (just an arduino and a couple of ds18b20) and are now measuring the temperature to and from the boiler and the outside temperature, so I can visualize them on a graph



I think the system is a one-string hydronic, and to me the return temperature seems pretty high. In Europe I would have expected the temperature to be around room temperature but that would be on a two string system. On the other hand the a boiler temperature of 60 Celcius (140 F) is probably not that bad, and it could be lower once the house gets fully inulated

I was thinking I could figure out my real current BTU need from this, f.ex. the boiler on-time should be easy to determine, but I do not really have a clear idea of where to go from there, any ideas,
I could also just look at the gas usage for say a 24 hour periode. or is there a simpler/better way.

The circulation pump is a Grundfos UP 15-42F

The house is tiimber-frame 1800 sqr feet from 1956 not really insulated at all, we have all ready put 2 layers of R30 loft insulation in on a third of the loft, there was 1" (read one inch), and can we already feel the difference.

I also found the answer to my other question, in Westchester county, all plumbing has to be done by a plumber registered in the county, but I hope I can design it.

The "freewatt" thing might be interesting, but I have no idea about the financial aspect, I red somewhere that a system would cost around $13000.   I was hoping to do my boiler upgrade for less than $3000, maybe that is unrealistic now everything has to be done by a Weschester plumber.   So an extra cost of $10000 would require almost $2000 savings a year, which is probably unrealistic.

It would probably be better for the environment to insulate the walls and to put in argon-filled double-pane windows. which we might do any-way.

/Peter

A boiler output temp of ~60C is about as low as you can go with cast-iron boilers without destroying it with condensation, and even that requires a "boiler bypass" to mix the return water with boiler output to keep it above 55C (condensation will occur on the heat exchangers with ~ 50C return water but condensation in the flue is a hazard with return water temps below 55C.)

What is your anticipated annual electricity cost, and what is your anticipated heating/hot water fuel cost? A Freewatt will produce ~5000-6000kwh/year, and at 15cent/kwh you're halfway there. Your fuel use is likely to fall by 30-40% since it's apparent that you'll be able operate in condensing-mode most of the time. If you're currently using 1500-2000 therms/year at $1/therm, that's another large chunk of that $2000 you seem to need to rationalize.

But think about it- how sane is it to demand a 20% return after-taxes on a $10K (or even 10% after taxes on a $20K investment, which is closer to the figure for a Freewatt hydronic). That, mi amigo is a ridiculous demand! Do a present-value analysis on it- I don't care what you use for a discount rate, but I expect the current prices for both electricity and natural gas are near a 10 year low, and they'll be increasing dramatically in the next 5-10 years.

Have you actually PRICED argon filled replacement windows for your house? Odds are it'll be the same order of magnitude money as a Freewatt, for far less return.

Do the math- cogenerator systems are quite a deal if your utility allows net-metering at full retail.