Terry Beck
03-25-2010, 06:59 PM
Can a standard 40 gal gas hot water heater be a sufficient source of heat for a radiant floor heat system?
Details:
8-10 yr old 1-story on slab, about 1200 sq ft
Northern latitude (montana) where we get usually get at least a few weeks of the year with -20 temps (we live in a more temperate part of the state)
Heat source is a Rheem natural gas 40 gal hot water heater rated at 38,000 BTU/HR input.
Plus - this hot water heater (and the domestic HWH) are both in an unconditioned exterior closet (R-19 wall insulation), with an exterior vent for combustion air. So the closet and plumbing must lose at least some heat anyway. Also, seems like a waste of energy maintaining the 40 gal tank at temperature at all times.
Of course, I have no details on the construction of the concrete slab. I can see 2" rigid foam insulation on the exterior of the slab foundation; don't know how far down it extends, or what is underneath the slab.
The temp setting on this water heater was set to max, and it was running continuously this morning when it was about 35-40 degrees (I was in short sleeves). When I do see the occasional radiant floor heat system, it usually has a gas boiler system with at LEAST 90-100,000 BTU input.
As a rule I don't comment on sizing of heating systems unless it is obviously very undersized. But this seems a bit 'on-the-cheap' even to me.
Luckily, the buyer plans to buy and install a wood stove anyway.
Terry
Details:
8-10 yr old 1-story on slab, about 1200 sq ft
Northern latitude (montana) where we get usually get at least a few weeks of the year with -20 temps (we live in a more temperate part of the state)
Heat source is a Rheem natural gas 40 gal hot water heater rated at 38,000 BTU/HR input.
Plus - this hot water heater (and the domestic HWH) are both in an unconditioned exterior closet (R-19 wall insulation), with an exterior vent for combustion air. So the closet and plumbing must lose at least some heat anyway. Also, seems like a waste of energy maintaining the 40 gal tank at temperature at all times.
Of course, I have no details on the construction of the concrete slab. I can see 2" rigid foam insulation on the exterior of the slab foundation; don't know how far down it extends, or what is underneath the slab.
The temp setting on this water heater was set to max, and it was running continuously this morning when it was about 35-40 degrees (I was in short sleeves). When I do see the occasional radiant floor heat system, it usually has a gas boiler system with at LEAST 90-100,000 BTU input.
As a rule I don't comment on sizing of heating systems unless it is obviously very undersized. But this seems a bit 'on-the-cheap' even to me.
Luckily, the buyer plans to buy and install a wood stove anyway.
Terry