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hot water radiant heat( boiler vs on demand )

15 years ago

I am adding a 1800 sq ft addition on to my existing 800 sq ft home. I bought a large boiler to heat the house because I new some day I would add on to the house. I just did not know it would be 15 years latter. I would like to buy something that is more efficient. I have been hearing rumors about a recirculation system that has a heat source like the (On Demand hot water heaters). If ther is such a heater I would not need a boiler system. If anyone knows the names or has info about them I would like to know.

Thank you

MC

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Comments (6)

zl700
15 years ago
If youÂre looking to upgrade to a new boiler, while an on-demand heater as a boiler would work, the low flow rate and expected longentivity in a heating application would make the choice on a whole house a poor one.

You should be looking at a modulating and condensing boiler with outdoor reset that will far exceed the efficiency of an on-demand.

Take a look at the Triangle Tube Prestige or Viessman for a quality product.
ferd42
15 years ago
Just some thoughts on improving your existing setup (it's probably got 20+ years' service life left):
1. Don't use a heating boiler for domestic hot water, especially in the summer.
2. Convert to gas if you're currently burning oil (and be sure to carefully clean heat transfer surfaces).
3. Provide as many zones as you can afford, schedule the temperatures with programmable thermostats; use one circulator with multiple zone valves instead of multiple circulators.
4. Arrange for fire on demand (if you have a cast iron boiler - don't do this with a steel boiler).
5. Provide a reset control to limit boiler temperature when it fires (I always liked Honeywell T475A); install the water sensor in the pipe, don't just strap it to the pipe surface. (This is another one not to do if you have a steel boiler).
6. Put in a stack damper (make sure it works properly).

Had a good time with this stuff in my first home, a 1930's semidetached; started with a new Weil-McLain oil fired and went from there, over a 24 year period.
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Chisue, I'd say 4K is probably not a bad bid. It is more expensive to retrofit than to install originally and it isn't quite as simple as just running some pipe under your existing floor. I don't see that the value of a 5K home in your neighborhood has much of impact on the conversation. From experience, the cost difference in many home retrofits and repairs in a high value RE value area, in the range you mention, and another in a low cost area, is not that much except when transportation costs of materials is at issue. In fact some services and inputs are more expensive in our lower home value area than in our higher value area, simply because more local trades that do higher end type installs are available and competing for work. From our experience we have to often hire someone from the nearby city --45 miles away -- to do the work and that does come at an up charge, understandably. There is also the fact that smaller jobs also cost proportionately more than larger jobs anywhere. It might help if you don't put down the trades as simpletons. If don't like the bid or can't afford that price, why don't you just go hire someone off the streets to install the tubing, direct the job yourself and just ask a master plumber to make a call to hook it up. LOL. Be sure to pull the correct building permit if ine is required -- it often is for additions to mechanical and plumbing systems.
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zl700
15 years ago
Correction/addition to FERD42:

A 92%+ low mass modulating and condensing boiler, coupled with an indirect water heater is capable of producing domestic hot water up in the 95% range in the summer.

Prestige Boiler:
http://www.triangletube.com/CondensingBoilers/PrestigeOverview.htm

Indirect tank:
http://www.triangletube.com/Residential/ProductIWH.htm
ferd42
15 years ago
That's combustion efficiency, right? I'd be concerned for seasonal efficiency, too; might be better off with a separate instantaneous domestic water heater.
zl700
15 years ago
Thats correct, boiler AFUE on a 110M is 93%

You would be hard pressed to find an on-demand gas over 83% unless you go with the newer 90% + but that will cost you, including the gas supply required to support both.
ferd42
15 years ago
Have to evaluate piping losses associated with the indirect, etc. to look at seasonal efficiency for the combo.

The gas piping may be undersized now; might want to have the PD checked. A pressure test is also a good idea anytime you're working on the gas piping; have found a lot of leaks in existing piping over the years. Basic safety there.

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