Geothermal heating question

[Dan Friedrichs]

Looking to build a new garage, and would like to install radiant floor heat (to keep the ice and snow off the vehicles, and to make working in there a little more comfortable in the cold winter). Was thinking of supplying the heat to the floor using a geothermal heat pump. However, this is just a garage, and I'd be perfectly happy with the temperature being 40-50F (just enough to keep things from freezing). If I installed a large geothermal loop, wouldn't the water temperature from the loop be 40-50F all year round? Couldn't I just directly connect the loop to the radiant floor tubing (with a circulator pump), and forget the heat pump, entirely? Certainly it wouldn't get very warm, but could be enough to keep it from freezing, and other than the cost of electricity to run the circulator pump, it would be free energy.

(In reality, I would likely install a secondary heat source if I did this. And, obviously, I need to do all the calculations to account for the cost of a heat pump, government and utility rebates for buying a heat pump, etc, etc - I'm just curious, on a theoretical level - if such a system would work)

[Lee Schierer]

Geothermal generally doesn't work too well with radiant heat. The ground water is probably about that temperature range, but you would have some heat loss from the garage that might be greater than the heat input from 45 degree water. Also unless you have a piece of equipment that meets the IRS criterion you wouldn't be eligible for any tax rebates. A simple water loop would not qualify unless you can tap into a hot spring. The forced air type system would be more effective and less costly to install in your garage.

[Ed Aumiller]

Radiant floor heat has much smaller pipe in it than what is put in the ground... so it requires a much higher water temperature to transfer the heat to the floor..
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A water to water geothermal system would work and be eligible for the 30% tax credit probably, but for a garage where you have such large openings it probably would not be that efficient..

You will be better off putting insulation in the walls & ceiling and putting in insulated garage doors... then installing a standard forced air geothermal system..

Note.... Geothermal heat pumps DO NOT heat an area quickly and are better suited for closed areas.. every time you opened or closed a garage door or brought 2 tons of cold metal into the garage it would take a while for the temps to recover...

I have geothermal in my house but put a propane furnace in my shop for that very reason..

If you decide to go geothermal and install it yourself (very easy) the best place I found for heat pumps is on eBay... determine size you need, look and then call them as prices are very negotiable...
Good luck...

[David G Baker]

Dan,
Something you may want to consider if you drive your vehicles in snow country where the salt the heck out of the roads. If your vehicles are stored in a warm environment after being coated with salt it will accelerate the corrosion caused by road salt.

[Jeff Nicol]

It has been done with a small water heater, but the main thing is that you must put insulation under the slab (2" foam w/taped seams) and then put insulation down along the sides of the slab 2-3' to stop the cold from getting in under the slab. Then with good insulation in the ceiling, walls and doors you will be able to keep it warm enough to melt and dry snow and water because once the mass of the slab is warm it won't take much heat in the water loop to do the job. They do make small boilers that will work too, but usually cost more $$ and also you would need to treat the loop with glycol so it won't freeze, just in case of a failure.

If you don't want it to be 65-70 degrees in the garage it will be fine, and if you are attaching it to the house that will help with a warm wall.


Good luck,

Jeff

[Ken Fitzgerald]

If you are considering using radiant heating in the floor and using a water heater as the source of heat, check what local code requirements would be to do it that way. I wanted so badly to do radiant heat and use a water heater as the source. To meet local code, it would require me to plumb water into the shop and then have some special safety circuits designed to shutoff the water heater under certain conditions. In the end it became financially infeasible for me. In the end, I have a Lennox hanging natural gas heater. It works well.

The key, however, is as Jeff pointed out....insulate under the slab and then walls and ceiling too!

[John Prexta]

I built my workshop in 2005, interior 24/40 ft, ceiling 9ft 5 inches. Man door, 5 large windows, 9ft wide insulaed overhead door. Concrete floor. 6 inch thick walls, heavily insulated, ceiling with 12 inches blown cellulose. Even during this very bad cold snap, it hasn't frozen inside my shop -hit 38 degrees at lowest point. I have woodburner, get a fire started, couple logs quickly bumps the space up to 60 - plenty hot for me.

I'm not parking a car in it, so I'm not opening the overhead door in the wintertime.

With your garage being well insulated, can you just get away with wall mounted gas heater? (if gas is available to you). To me, that'd be enough to knock out the chill. Good luck

[Larry Edgerton]

Dan,
Something you may want to consider if you drive your vehicles in snow country where the salt the heck out of the roads. If your vehicles are stored in a warm environment after being coated with salt it will accelerate the corrosion caused by road salt.

Big +1. The cars that come in to my brothers repair facility that are stored in heated garage last about half as long.

Larry

[Greg Portland]

I've had wall mounted heaters in the past (HotDawg, etc.) and I have in-slab radiant in my current shop. The radiant heat is superior in every possible way (comfort, dust movement, cleaning, operating cost, etc.). Geothermal loops are very pricey, I'd look at a high efficiency water heater or boiler instead.

[Chuck Wintle]

Dan,
Something you may want to consider if you drive your vehicles in snow country where the salt the heck out of the roads. If your vehicles are stored in a warm environment after being coated with salt it will accelerate the corrosion caused by road salt.

I will second this comment...a heated garage and a salty car will rust way faster. Better to leave them in a cold area if they salt the roads as they do here.