Concrete Floor and Garage Heaters

[John Peterson]

Hey all,

As funds allow, I'm insulating and drywalling the 3rd stall of my garage. I'm also putting up a wall to isolate the shop from the 2 car portion of the garage which will be insulated but not heated. I plan to use a "hot dawg" style hanging furnace for the shop. I figure I'll use a programmable thermostat for the furnace. So that when not in the shop the temp remains around 50 degrees or so then 60 or so when in the shop.

Here's my question. Talking with a guy at work he said that in his shop once the concrete floor warms up the floor will act as a heatsink. Now, this makes perfect sense, but this is also the same guy that will "one up" everything you have or do. Is he right?

[Art Mulder]

Yes.

The concrete acts as a thermal mass. think about how the rocks at the beach get hot in the sun, and are still warm for a while after the sun goes down.

Now, with a three car garage, is the slab monolithic, or are their breaks in the slab between the stalls? I have no idea if the heat radiate "sideways" through the slab.

[Jeff Sudmeier]

Yep, it will act as a heat sink... That's why if I ever build a house the basement floor and garage floor will be insulated under the concrete, cheap and keeps your feet slightly warmer.

[Rod Sheridan]

As others have indicated the concrete has thermal mass.

It will warm up slowly as it stores energy, then cool slowly when the heater is set back.

It won't save you any energy, it's just storing the energy you already paid for.

Regards, Rod.

[Tom Godley]

The difficult part is heating the floor.

In my shop the floor (concrete) never gets all that warm. I have never taken its temperature but it always feels colder than the walls. I keep the place around 58 and turn up the heat when I want to use the space.

Unless you have an insulated floor that is directly heated -- don't plan on it helping in the heat department.

[Ed Harrow]

Hey all,

... Talking with a guy at work he said that in his shop once the concrete floor warms up the floor will act as a heatsink. Now, this makes perfect sense, ...

If the shop spends most of the time 'heated' the slab would tend to stabilize 'warm'. If it spends more time unheated... The best thing I did with respect to comfort was to insulate the floor, plus it's way easier on feet, legs, knees, and tools. YMMV.

[John Peterson]

The difficult part is heating the floor.

In my shop the floor (concrete) never gets all that warm. I have never taken its temperature but it always feels colder than the walls. I keep the place around 58 and turn up the heat when I want to use the space.

Unless you have an insulated floor that is directly heated -- don't plan on it helping in the heat department.

I think this about sums it up. Im pretty sure there isnt any insulation under the slab. And the only seperation to the rest of the slab isthe cuts they made to control cracking.

My original thought was to do an OSB floor. I know in the past that my feet got cold pretty fast on in the garage, although this was with un insulated walls, and a propane torpedo heater.

[Joe A Faulkner]

John, in my case, I have a detached two car garage. I plan to put down 1.5 rigid foam board between pressure treated sleepers, 16" on center. You might be interested in the thread found at http://www.sawmillcreek.org/showthread.php?t=135593 where fellow creekers have commented further on insulating slab floors. I am also thinking about a hot dawg, though if I go that route, I am considering the extra money for a unit with separate combustion (draws combustion air from outside). Hope this helps.

[Rob Lindquist]

I use a Hot dawg style heater in my shop, detached 26 X 40. I did insulate under the slab, and also instaled radiant heat in the slab but never hooked it up yet (initial cost and slow reactin time holding me back) so I just use the Modine for it's quick heating. I don't think the insulation underneath helps all that much compared to my uninsulated garages, maybe just a bit.

I strongly suggest installing a ceiling fan, or at least wall mount a fan across from the Hot Dawg blowing the heat down to the floor and back toward the Hot Dawg. It will help a LOT creating even heat floor to ceiling, and wall to wall, althought the slab still be chilly, you won't be cold from the knees down.

[Don Jarvie]

The concrete will remain cold unless you can keep the heat on.

I have a Dayton G73 and the shop is insulated and gets the shop to 45 to 60 in 40 minutes or so but the concrete floor still reamins cold.

You can actually feel the cold in the floor if you drop something.

The advantage in insulating the floor besides the comfort is it will take less time to heat the room since the floor won't be as cold and that air will warm up faster.