Advice needed on old radiant heating boiler setup
Last Post 01 Feb 2024 02:42 AM by JTO. 22 Replies.
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cacophonyUser is Offline
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09 Aug 2015 11:34 PM
I have a very old boiler setup that's original to the radiant heating system in a 1947 house (slab foundation). It's been pretty reliable over the years. I've had a few different plumbers and a radiant heating person out over the last 10 years to do minor fixes (eg. new thermocouple) and adjustments. Nobody that has been out has been that familiar with this old equipment.

Here are some photos:
http://tinyurl.com/pdgncx8

As you can see the water heater is in a rather inconvenient location!

For the radiant heater boiler, the pilot light and thermocouple are being held in position via some strategically placed wires. I think there are supposed to be screws but they are long gone.

I recently had a gas leak in the back of the closet where the line comes in, and the plumber I called needed to remove both the boiler and water heater to do the repairs. Unfortunately, after hooking everything back up the boiler seemed to no longer fire up (pilot light was fine, though). So now I'm thinking about how best to get this diagnosed/fixed. There's also safety concerns about the whole setup that I've wondered about over the years.

Any recommendations on how to find someone more familiar with this system? Is it time to think about replacing some/all of this, and if so, what would you suggest? What are the practical options here?

My knowledge in this area is quite limited, so whatever advice you have would be appreciated. Thanks!
Dana1User is Offline
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10 Aug 2015 10:56 AM
Seriously, when a boiler is old enough to be collecting Social Security (had it been contributing), it's well past time for retiring it. Looks like there is some scrap copper value left, but there's no point to spending money on repairing it.

To figure out what to replace it with requires a bit of math. If you have a ZIP code and a fuel use history on it it's possible to size the replacement correctly (some mid to late winter gas bills, and the exact meter-reading dates would do). A small wall-hung finned copper water tube boiler or modulating condensing boiler correctly sized would cut fuel use a bit (maybe even quite a bit- like half), and should improve reliability going forward.
Blueridgecompany.comUser is Offline
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10 Aug 2015 12:41 PM
Sir,
Your boiler is a thing of beauty from a bygone era,
nice casting, elegant in design, but I tend to agree with Dana,
Time to change her out. A simple heat only wall mounted condensing boiler would be a good choice.
Looks like a copper pipe in slab home, A lot of these were built in that time frame in the SF bay area buy a gentleman named Eichler, there referred to as Eichler homes.
That aside a location and square footage will help with what you might need for a boiler size. It is doubtful you have any insulation under slab and from the photos looks like there is no mixing or tempering of boiler water. Whoever does the work changing out the boiler may want to remove the black iron pipe and push the system to all copper, or perhaps a pex pipe bridge between the copper in slab and boiler to help isolate stray current from boiler and copper in slab.
Any way, nice boiler, has served you well,
Perhaps now yard art,
Dan


Dan <br>BlueRidgeCompany.com
BadgerBoilerMNUser is Offline
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10 Aug 2015 12:47 PM
Good information Dan. I wish I could get this unit to Minneapolis. It would be a nice addition to my museum.

We design many retrofit systems for slab-on-ground systems. The new condensing boilers will allow outdoor reset, which will keep the operating temperature as low as possible making the floors warmer more of the time and perhaps prolonging the life of the copper radiant floor system.

Given the tight space a combi-boiler e.g. Bosch, Viessmann or Navien for space and DHW in one package. Care must be taken to properly size and install such units. Find the right contractor, already familiar with such systems. The vendors may give you direction.
MA<br>www.badgerboilerservice.com
cacophonyUser is Offline
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10 Aug 2015 01:03 PM
Thanks for the responses!

Zip is 94303
Highest gas usage last winter was in January at 73.10 Therms
Square footage is 1340, but there's no radiant heating 't under the remodeled kitchen or back bathroom, so maybe only 1000 Sq ft of radiant heating.
Dana1User is Offline
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10 Aug 2015 02:26 PM
Space heating could be run as a plate-heat exchanger isolated loop off the water heater at your loads in Palo Alto.

Without the exact dates between meter readings we can compare that to weather data for 94303 to come up with an upper bound for the space heating load. It's likely that half or more of that fuel use was for domestic hot water anyway. But it makes a difference if that was the use between say, 20 December and 18 January, vs. say, 2 January & 30 January, or some other. Not every day in January has the same outdoor temperature, so we need to look up which heating-degree-days apply to that 73 therms of fuel usage.

According to the data from Moffett Field on Degreedays.net  Palo Alto experienced 416 HDD (base 65F) for the whole month of January.  If that was the exact billing period, that's 73.1 therms/416 HDD= 17572 BTU/HDD, or (/24=) 732 BTU/degree-hour.  The absolute best-case efficiency you're getting out of the beast is 80% thermal efficiency, but it's really probably only 60%, but just fer yuks let's call it 80%. That means of the 732 BTUs going into the burner, only (0.8 x 732=)586 BTUs went into the heating system (the rest went up the flue.)

Palo Alto's 99% temperature bin is +38F, which is (65F-38F=) 27 heating degrees, for an implied all time ridicuously overstated heat load of 27F heating degrees x 586 BTU/degree-hour = 15,822 BTU/hr.

That's about half the output of a run-of-the-mill 40 gallon gas-fired tank hot water heater.

In reality only half the fuel went into the antique boiler, implying a heat load of no more than about 8,000 BTU/hr which is a credible heat load for a 1300'  1940s house at +38F.

The only real question is the water temp requirements of the floor, but this sure looks like a cheap loop off the water heater is going to be the "right" solution, and a heluva lot cheaper than a new hydronic boiler.



Blueridgecompany.comUser is Offline
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10 Aug 2015 03:39 PM
Should you chose to use the water heater as Dana suggest there are several ways to accomplish that.
Here is a link to a simple prefabricated system we distribute based on the TACO X Block . This will attach to the hot and cold outlets of your water heater isolating the potable water from the heat water, very simple application with some clever built in functions including outdoor reset.
http://www.blueridgecompany.com/radiant/hydronic/767/rht-prefabricated-1-zone-x-pump-block-panel
Dan
Dan <br>BlueRidgeCompany.com
Dana1User is Offline
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10 Aug 2015 04:52 PM
I'm starting to wonder if some part of CA Title 24 would get in the way of a retrofit isolated loop on a non-condensing HW heater, requiring you to do something else(?). It may depend on the local building department, but it's insane to be patching the antique (no matter how cute it is) rather than heating at ~80% steady-state combustion efficiency (or higher) with a hot water heater.
cacophonyUser is Offline
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10 Aug 2015 11:33 PM
Posted By Dana1 on 10 Aug 2015 02:26 PM

Without the exact dates between meter readings we can compare that to weather data for 94303 to come up with an upper bound for the space heating load...




If it helps, here's some more info. Over the last two years my highest gas usage occurred in the following two service periods:

12/23/2014 - 1/21/2015 : 73 THERMS   <---- I should have been more clear that this was the January bill, not for service in January
11/22/2013 - 12/24/2014: 110 THERMS

All the other months are substantially less, and in the summer it looks like I'm at about 15 THERMS

This is for a 2 person household with (I think) a 40 Gallon water heater, occasionally used gas stove, and a continuously running pilot light in the old boiler.
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11 Aug 2015 09:47 AM
We use Polaris and Vertex with the Taco X-block as Dan and Dana suggest. You want sealed combustion and direct vent.

The XPB will give you outdoor reset. We use this setup often on the Left coast and more often here in Minneapolis for air-over-radiant systems for walk-out basements replacing failed Bradford White Combi-Cors when appropriate.
MA<br>www.badgerboilerservice.com
cacophonyUser is Offline
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11 Aug 2015 02:03 PM
I really appreciate all the replies. I'm a bit confused about all the options presented though, partly because I'm not familiar with much of the terminology.

I feel like I need to do some research before I can ask any intelligent follow-up questions:

water tube boiler (same as sealed combustion?) vs modulating condensing boiler
meaning of outdoor reset ?
meaning of combi-boiler ?
meaning of DHW ?
meaning of XPB ?
TACO X Block suggestion would only be applicable for existing water heater (which is "water tube boiler?) ?
BadgerBoilerMNUser is Offline
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11 Aug 2015 02:13 PM
http://www.badgerradiantdesigns.com/hotwater.html
MA<br>www.badgerboilerservice.com
Dana1User is Offline
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11 Aug 2015 05:22 PM
From 11/22/2013-12/24/2014 Moffett Field logged 539 HDD, and you used 110 therms...

...which is 20,408 BTU/HDD or 850 BTU/degree-hour.  Assuming against all reason an 80% efficiency, that's 680 BTU/degree-hour.

With a design temp of 38F and a base of 65F for 27 heating degrees, that's a maximum implied heat load of 27 x 680= 18,360 BTU/hr.

That's an insanely high number for a house that size- I'm assuming higher than normal hot water use was behind that.

From 12/23/2014 - 1/21/2015 they logged 454 HDD, you used 73 therms. That's 16,079 BTU/HDD, or 670 BTU/degree-hour.  At 80% efficiency that's 536 BTU/degree-hour x 27 degrees is a maximum implied heat load of 14,472 BTU/hr.

If you assumed 15 therms of that was hot water (it's probably more than that, since incoming water temps are lower in winter, and hot water use generally goes up in winter), which would mean 73 is really 58 therms for space heating, and the implied load is (58/73 )x 14,472 BTU/hr= 11, 500 BTU/hr, which is on the high side for a house that size, but OK. It's still well under the burner-output of a hot water heater.

Reality is that the beastie boiler is more likely to be delivering something closer to 60% efficiency, and the real heat load is 10-11K.

Definitions:

A water tube boiler is non-condensing heating boiler that's a bit more tolerant of low system water temperature than some other types of  boilers (important for radiant slab heating, which can destroy a cast iron boiler if not set up properly).  A modulating condensing boiler has a variable flame and can run at very low temps and higher efficiency by recovering the heat of vaporization of moisture in the exhaust stream. But your loads are so tiny the don't really call for separate appliance for space heating, so you really don't care (or shouldn't.)  Your antique is a variant of a water tube boiler. Modern versions have fins on the tubes to improve heat transfer efficiency. The fact that yours is fin-less means it's probably well under the 80% combustion efficiency used in the fuel use analysis. (A really GREAT finned water tube boiler can hit 87% efficiency, most are in the 78-83% efficiency range.)

A combi-boiler is an appliance that combines space heating and potable hot water heating in the same unit.  They come in many types & sizes (including a plain old water heater with an internal heat exchanger to isolate the heating system water from the potable water.)

DHW= Domestic Hot Water= potable hot water safe to use for bathing, drinking etc.

XPB is the model name of the Taco X-Block hardware that can be used for running isolated space heating loops off a hot water heater.

Outdoor reset:  heating system controls that raise or lower the heating system water temperatures in response to the outdoor temperatures, which is somewhat more comfortable for the occupants, and can mean higher efficiency for condensing boilers.
cacophonyUser is Offline
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12 Aug 2015 01:42 PM
Thanks!

So it sounds like the consensus is that a loop off the existing water heater makes the most sense, but I could also consider a combi-boiler if I'm willing to spend a bit more money?
But it's possible the Palo Alto building code might not allow a loop off the existing water heater?

I'm also wondering how much sense it makes to invest in a new radiant heat source when the actual piping under the house is almost 70 years old. Is is it possible the rest of the system could be near the end of its life soon and require prohibitively expensive repairs? Could installing a new heat source accelerate piping issues or leaks due to different water pressure, temperature or other characteristics? I've heard that some others in the area have changed to forced air heating from above, and that's clearly the most expensive of all options. I just want to avoid spending lots of money to fix up a system that might end up being a dead-end in terms of practical options.

Lastly, any suggestions on how to find a good local shop to do this type of installation?
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12 Aug 2015 02:01 PM
If you keep budget in mind,
use the prefab X block,
the pressure to the in floor can be held at 10 PSI,
The loop off the water heater is isolated from the slab heating water by the heat exchanger built in to the x block
Look at the manual to better understand. http://media.blueridgecompany.com/documents/X-Pump-Block.pdf
A new condensing boiler will run about 2-4+ times the cost depending on contractor and prevailing wages (you are not in the low rent district).
Th Eichler homes copper oddly seems to be holding up, I have talked with several contractors over the years that have worked on these.
The key is to be sure you can isolate stray currents from the copper, thus the pex pipe between supply and return of the manifold will help.
Dan
Dan <br>BlueRidgeCompany.com
Dana1User is Offline
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12 Aug 2015 02:13 PM
You'd have to present the design to the local building permitting authorities to find out if it's code legal. You may be able to clear that up with phone call or email.

The anticipated longevity of the radiation is a legitimate thing to question given it's age & ilk. It may very well be time to bail on using the floor as the radiation. If you're doing a major re-flooring you could put down some Roth panel or something, but retrofitting radiant floor radiation a real project and a serious chunk o' change. Alternatively, with a few low-temp flat-panel radiators you could micro-zone it and still use the hot water heater as the heat source. It's much cheaper than retrofit radiant floor, but still a long term investment in comfort & efficiency (not that it would ever "pay off" on efficiency.)

There are few (or no?) hot air gas furnaces with output as low as your actual heat load. A hydro-air system with a tiny air handler running off a hot water heater is a standard solution in some parts of California due to the low heating loads, but that's not necessarily the "right" solution either.

If you don't already have air conditioning a high efficiency heat pump solution might have the highest value-add, but would also come with a higher upfront cost. OTOH if it's just one part of the house and it could be both & heated/cooled with a 3/4 ton ductless mini-split (highly likely) the upfront cost might not be all that huge ($3-3.5K in my neighborhood). A decent one with a good modulation range and not a crummy $800 1 or 2 speed is quiet, comfortable, and super efficient. It's not as cushy as warm floors or panel radiators in heating mode, but it's quieter and more comfortable than 99% of the hydro-air systems, and 99.99% of the gas fired hot air furnaces out there. A better-class mini-split will air condition at super-quiet, very high efficiency too.
cacophonyUser is Offline
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07 Jan 2024 06:30 AM
I'm bumping this old thread because I'm finally getting around to having this work done!

To summarize, this is for a ~1340 square foot house in Palo Alto with 2 full bathrooms. Current boiler is a Hotstream 192-L from 1947 (label says "NAT. 60,000 MED 75,000 BTU PER HOUR") and current water heater is 40 gallon (38k input BTU).

I've contacted a couple reputable radiant heating places and one place gave a bid with the IBC SFC 199 and another with the VIESMANN B1KE-120.

Any thoughts on these choices? And can someone comment on the sizing difference and what would be more appropriate?
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08 Jan 2024 03:55 PM
Dana gave you great advice nearly 10 years ago. I think Dana still provides guidance and can maybe be found on Green Building Advisor Forum:

https://www.greenbuildingadvisor.com/

As Dana recommended, it makes zero sense to get a gas boiler for this miniscule heat load. I would recommend a small electric NextGen Boiler which is designed expressly for hydronic radiant heating which will save you much money and will save you even more money from NOT needing a hydronic radiant panel (controller, pumps, expansion tank, differential pressure valve, pressure relief valve, air removal valve, etc.):

https://www.nextgenboiler.com/

Or better yet, abandon hydronic radiant and just use a much more energy efficient mini split system...again like Dana recommended...
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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08 Jan 2024 08:14 PM
Posted By sailawayrb on 08 Jan 2024 03:55 PM
Dana gave you great advice nearly 10 years ago. I think Dana still provides guidance and can maybe be found on Green Building Advisor Forum:

https://www.greenbuildingadvisor.com/

As Dana recommended, it makes zero sense to get a gas boiler for this miniscule heat load. I would recommend a small electric NextGen Boiler which is designed expressly for hydronic radiant heating which will save you much money and will save you even more money from NOT needing a hydronic radiant panel (controller, pumps, expansion tank, differential pressure valve, pressure relief valve, air removal valve, etc.):

https://www.nextgenboiler.com/

Or better yet, abandon hydronic radiant and just use a much more energy efficient mini split system...again like Dana recommended...

The therm usage numbers I posted earlier in this thread are not accurate. I was rarely running that radiant boiler because of safety and inefficiency concerns and was fine with indoor temps in the 60-65 range. Now I would like to be able to make the indoor temp more comfortable. I'm fairly confident the therm usage would be significantly higher if I just left the thermostat at 67 or higher. That boiler uses about .66 therms per hour when running and never seems to get the water temp high enough to turn off, so I wouldn't be surprised if it was close to 20 therms per day.


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09 Jan 2024 01:45 AM
Well, you first need to accurately determine the required heat load before selecting the heat source.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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