Boiler vs Water Heater?
 

I'm trying to decide how best to get some heat in my 1500 sf detached garage in Wisconsin. (Best = lowest operating cost.) My goal is simply to keep the building above freezing, probably 40-45F. The PEX is already in the slab, but not hooked up yet. Natural gas is available in the garage.
I've been researching to figure out whether I can use a low-end water heater as the heat source or if a real boiler is worth the extra cost. There seem to be good arguments both ways. I assume the water heater will be somewhat less efficient, but any heat lost will still be inside the building so it may be a wash. I only plan to run it during the coldest 3 months or so if it matters. I plan to use glycol in a closed system (no DHW) so potential freezing is not a concern.
The building is pretty well insulated and it already stays around 30F even with no heat (outside temp between 0 and 10F). There's a 2" polystyrene board under a 6" slab and up the sides. The walls are 2x6, fully insulated, and drywalled. I also put in about 8" of insulation above the drywalled ceiling. All doors and windows are well-insulated and tightly installed.
Any suggestions from the experts?

Hello
 

Hi..

You haven't gotten any responses so I thought that I'd give it a try..

I'm a Plumbing & Hydronic Heating (Radiant) Contractor.

Nothing wrong with using a water heater for the heat source. If the garage is tight a 40 gallon 40MBTU would be fine. 60/40 mix with glycol and away you go.. A slab sensor vrs an air sensing t-stat would be best if still possible.

Any other questions please don't hesitate to ask..

:-) Ken
The K.C. Ament Co., Inc.

Thanks for jumping in----Some times posts get overlooked---this one sure did.

---Mike---