Radiant slab for a basement garage?

[Badfish740]

I'm one of those people who refuses to pay for any service I can do myself, so of course I change the oil in both of our vehicles with good reason-an oil change in my truck alone costs $60 as it is with a Motorcraft filter and 15 quarts of 15W-40. By the time a shop gets done marking up the oil and filter and bangs you for the labor it can go north of $100. However, saving that $40 last night didn't feel as satisfying as it did during the winter months. 16 degrees, ice on the driveway (truck is too tall for the garage), and a steady breeze blowing made for less than ideal conditions. I swore to myself that our next home would have a heated garage. However, even though I plan on going with a gasifier and am not going to be throwing money away on propane or oil, the thought of committing the amount of BTUs it would take to keep the garage toasty during the winter months isn't all that palatable either. That's when I had an epiphany-why not build the house on top of the garage? My in-laws have a raised ranch with a two car garage occupying half of the basement-it's unheated however. My thinking was this-if I were to go with a heated slab for the basement/garage floor (well insulated) I could dump a bunch of heat into it knowing that it's not going to waste because the slab would heat the air which would rise and contribute to heating the entire house (which would also have radiant underfloor heat)-good idea/bad idea?

 

[midwestcoast]

I like the idea of using a basement for a garage as it seems a good use of space plus gives bay door access to the basement. I don't see anything wrong with that approach but I would be conserned with:
Meticulously sealing the garage off from the rest of the house to keep exhaust and other fumes from migrating into the living space. Sealed doors too and also providing ventilation to the garage.
Would want a very well sealed and insulated garage door. I imagine they are out there.
Need to plan the lot grading so the driveway grades away from the house the keep water away from the basement and foundation. Many I've seen just rely on a grate drain in front of the garage door and those are always getting plugged-up.
I'd likely put the garage on a seperate zone so I could just crank it up when I had work to do in the garage.
I've no idea what most codes say about this these days. I guess you'd need fire breaks all around?

 

[Badfish740]

I like the idea of using a basement for a garage as it seems a good use of space plus gives bay door access to the basement.

My in-laws house is not all that large (raised ranch, 3 bedroom, 1 bath) but with half the basement devoted to garage space, and the other half a family room and laundry area, it's quite comfortable.

Meticulously sealing the garage off from the rest of the house to keep exhaust and other fumes from migrating into the living space. Sealed doors too and also providing ventilation to the garage.

I guess this is where it gets tricky. My in-laws garage is sealed because its un-heated, so obviously you want to stop air infiltration from a heat loss standpoint. In this case I don't care about air infiltration in terms of heat, but I also don't want garage fumes traveling upstairs. Exhaust I wouldn't worry about. No need to idle the vehicles to warm them up on cold mornings with a heated garage (my diesel will love it), but I suppose for some repairs I might need to run the engine inside the bay-I could always get a good heavy duty exhaust hose like commercial shops use to run it out the door.

I'd likely put the garage on a seperate zone so I could just crank it up when I had work to do in the garage.

Definitely. Lying on a slightly warm concrete floor while doing maintenance would be priceless.

I've no idea what most codes say about this these days. I guess you'd need fire breaks all around?

I'm sure it varies from place to place-I think it would be one of those cases where exceeding code would be good for peace of mind.

 

[jimbom]

I have radiant in my basement but don't use it. Without any heat input, the floor surface is about 60 F in the winter. Decouple the slab from the walls by surface to soil insulation completely around the edge of the slab. Most of the loss is in the edge and if you stop that, the ground will keep things perfect for working on cars, tools, guns, etc. Two inches of blue board edge would help a lot.

 

[Dune]

You can't crank up radiant heat when you need it, the only disadvantage it has. It takes a while to heat a few tons of concrete. However, the beauty of radiant slab heat, especialy in a garage, is that even if you open the door (garage door) for ten minutes on a supercold day, the slab stays warm. Shut the door, and you feel warm within minutes. My advice would be, build a freestanding or attached garage, install radiant slab heat, superinsulate the garage, run the heat at say 40-50 degrees in the slab. Also install a modine style heater for bringing up the room temp quickly, if you want to work in there. Unlike a house which can be overinsulated and suffer bad air quality, you could insulate and seal the heck out of your garage, keeping the cost of heating pretty low.

 

[GaryGary]

Hi,
Seems like a basically sound idea that should decrease the cost of heating the garage.

But, the garage walls still loose heat -- so you would want good insulation, and cold air infiltration can be bad in garages especially around the big doors. Heat loss through the big doors can be pretty large also as they are not heavily insulated -- maybe R6 on the good ones. Radiant heated slabs that are not insulated under the slab loose quite a bit of heat down into the dirt. But, I think if you did a good job of working all those garage heat loss sources


If you have a good south facing wall or the big doors face south, you can solar heat the garage on sunny or part sunny days. Just wait for the sunny day to change the oil.


Solar shop/garage heating that uses the garage door opening -- my all time favorite solar project -- good heating and great lighting!
http://www.builditsolar.com/Projects/SpaceHeating/SolarGarageCollector/garcol.htm
The nice thing about this one is that you could insulate under the slab, and let the sun shine on the slap a couple hours before you pull the car over that spot for the oil change

Solar heating a shop/garage using the south wall:
http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm


I carpeted my shop with the old carpet we pulled out of the living room when we went to hardwood floors. Takes away the floor chill and makes a nice surface to work on.


Gary

 

[Hydronics]

I built our house this way, 32' x 41' garage with living above. I insulated under and around slab & put in 5 - 250' radiant loops. The garage thermostat is at 50 & the radiant zone never runs. I get enough heat off the boiler/zone feeds to keep it 55 to 60. r19 in walls and r17 10'x10'oh doors. You'll need 5/8" sheetrock for firecode and a fire door to living space. I'm quite satisfied with the setup though the Wife wants more living space.

 

[xman23]

The issues that I can think of'
The radiant heat will take so long to bring up to temp, and so inefficient you will find yourself not using it.
The not needed garage heat will raise car fumes thru the house.

I'd spend the money on a jack and a creeper to lay on

 

[semipro]

...Meticulously sealing the garage off from the rest of the house to keep exhaust and other fumes from migrating into the living space. Sealed doors too and also providing ventilation to the garage.
...

Our garage is under our house. Fumes and dust moving upstairs is is a major issue, one I would not underestimate.

I wouldn't even consider heating the slab unless it was insulated underneath.

I suspect that if you insulate the slab and insulate the side walls you may find that its warm enough.

My suggestions if you put the garage under the house:

- insulate the slab and walls
- put the tubing for radiant in the garage slab but don't hook it up to anything
- try it out. You may find that you don't need to heat the slab but if you do, the tubing is there
- seal the heck out of the garage and possibly add some small exhaust fan like the ones used for radon ventilation to create a negative pressure in the garage when needed
- consider a 10ft high basement. I'm constantly breaking lights and having problems because my garage ceiling is at 8ft.