water heater for radiant heat source?

oldnewbie

hello, we are building a new house with a basement. It will be a 1800 sq ft ranch with a full basement and standard forced air nat gas hvac system. Half the basement will be finished space with a bedroom. The plumbing contractor roughed in radiant tubing in the entire slab,using insulation around the perimeter and under the concrete. The plumber wants to use a 50 gal water heater for the heat source, using one pump. We have a standard water heater supplying domestic hot water. I have been told a modulating boiler with an outdoor reset (such as a Navien)would be a better choice. These boilers have stainless steel heat exchangers and snazzy circuit boards but since this is not our primary heat source, I'm leaning toward simple . Any ideas on water heaters  or even electric boilers?( I have not done a heat load calc yet)

Charlie from wmass

Boilers are boilers

They have been tested and approved for use as heating plants. What are of the globe are you from? Electric would be very costly here in Massachusetts but would make sense in Oregon or Ontario with their cheap hydro electric rates.

NRT_Rob

depends

on what you mean by water heater. there are a few high end modulating and/or condensing water heaters out there that do well as heat sources.



Or, if your heat load is very low, a water heater can work well. always separate heating from DHW with a heat exchanger though.



Electricity can make sense these days compared to propane or even oil. much cheaper up front and not that much more to run these days .... up here in maine, once you take into account an oil boiler's summer inefficiency for DHW, you might even save money on electricity right now. Times they are a'changing...

Jells

Under what circumstance would a WH be right?

NRT_Bob, didn't you used to post actively on RadNet? What happened to that site?  Anyway, I remember there you were advocating water heaters for radiant.  Would it be a good solution for 1000 sq ft rowhouse apartments?  4 WH's sounds more cost effective than individual boilers & heat exchangers. Right now they all get their DHW from a 75 gal tank, I can keep footing that bill if it saves many thousands off of what would be required to provide both radiant & DHW for each from individual units.



BTW, the system under consideration would be a pex ceiling retrofit over old plaster. Seems like a 2fer to me, as the ceilings need major work anyway.

SWEI

or you could

Install a single mod/con boiler serving all four units along with a networked thermostat system (Uponor CCN, Tekmar tN2, etc.) and build the utility cost into the rent (along with a bit of margin to help amortize the CapEx you just incurred.)  Individual small residences in mild to moderate climates are just not a great fit for currently available gas-fired mod/cons, but groups of 2-10 work nicely.

Jells

Yeah, that almost an entirely other question.

I was just discussing that with the wife. Our other 8 apartments are all on their own heat bill, and it's nice not to have to deal with it.  But the capital expense to separate these 4 is pretty large, and the gain isn't perfectly clear for the reason you raise: they're not rent controlled and I can build it into the rent.  But when fuel costs are unstable this can bite you in the ****.  So I'm weighing what I've proposed upthread vs just replacing the oil guzzling boiler ( apparently well oversized according to Jstar) with a new gas one, and keeping the steam radiators.  This complex a problem can make your head hurt!

NRT_Rob

the RPA

changed hands and they let the old site go down, unfortunately. Lot of collected wisdom just poof! such is life in the cloud.



a water heater would probably do well in apartments. your heat loads are probably very small. but math should be done to verify.



a single heat source has advantage but little payback in these circumstances. better than 4 boilers though for sure.