House Furnace/AC in Garage

[rl_sd]

I am looking at putting up a 30x36 detached garage and have been throwing around the idea of heating and cooling it w/ a house furnace. I have the line on a cheap 80%, coil and compressor for < $400. I figured that I would go w/ 80% so that I could shut the heat off in the winter if I wanted too (Non-condensing furnace). Has anyone else done this? Pros/cons?

[rundrave]

What type of construction, stick or post frame? How will you have it insulated?

 

have you considered in floor heat?

I built a 28x32 detached garage a few years ago. When I poured my floor I put the pex down. I dont have anything hooked up yet but its on to do list. I did 2x6 construction with spray foam walls and blow in insulation in the attic. It stays pretty warm just as it is with no heat out there yet.

 

 

Edited March 11, 2020 by rundrave

[rl_sd]

Stick built, 2x6 walls, 10' ceilings, batt and blown. Thought about putting together a floor heat system, but the cost of the boiler system has me thinking otherwise.

[delcecchi]

Sounds like a good way to go to me.     Take a long time to make up the difference in price.   

[rl_sd]

Thanks Del. I was wondering for those that have did it before how the recovery time was after opening doors or coming up to heat after a few days. I’d like to run it 40 deg during the week but bump it up to 50-55 when I am out there. I’m hoping with a 75k btu that my recovery time will be short. 

[Wanderer]

36 minutes ago, rl_sd said:

Thanks Del. I was wondering for those that have did it before how the recovery time was after opening doors or coming up to heat after a few days. I’d like to run it 40 deg during the week but bump it up to 50-55 when I am out there. I’m hoping with a 75k btu that my recovery time will be short. 

The recovery time is slow for in floor heat.  If you’re going to open the doors on a regular basis I’d give more consideration to forced air.  If not, I’m sure you’d be fine.  In floor is also slow to dissipate.  In a garage, you’d either need to add glycol to the system or have a back up heat source in case of failure for freeze protection.  Adding glycol isn’t a huge deal but it decreases efficiency a bit and adds another maintenance item manage.

Fun project though!  I built one of similar size at my last house but didn’t hang the heater.  I found I didn’t spend as much time out there as I expected.  Sad thing is I moved the heater with me!

 

If you want a 100,000 btu Reznor with a 10 inch stack. Let me know!   It was take out from a warehouse.  I don’t think I’ll ever use it at my current house.

 

[delcecchi]

2 hours ago, rl_sd said:

Thanks Del. I was wondering for those that have did it before how the recovery time was after opening doors or coming up to heat after a few days. I’d like to run it 40 deg during the week but bump it up to 50-55 when I am out there. I’m hoping with a 75k btu that my recovery time will be short. 

 

My daughter has a 3 car attached garage with one of those hot dog type heaters.   Opening the door for a short time and then closing it doesn't seem to have too much effect.   The problem with heating up from 40 to 55 or so that will take a while is that the floor and walls and the contents are all cold and take a while to get up to temp.  so the air might be warm but heater will need to work harder because of all the cold stuff in there.   

 

If I did the calculation correctly, heating the air takes about 200 btu per degree or 3000 btu for 15 degrees F.  If your furnace puts out 60k (75 k input) that is 5% of an hour's worth or a couple minutes.   

 

Seems like not much, but it doesn't take much energy to heat 9000 cubic feet of air.  Please feel free to check my numbers, since I did the arithmetic in my head and I could easily have misplaced a decimal point.    

[Grainbelt]

I had purchased a used 80k btu house furnace for my garage only to find out it was against code to put in there. Combustible fumes at floor level was the reason why. I sure liked the radiant tube heaters but did not have enough height to install. They heat the objects in the garage, and can bake paint on the car if installed too low. I ended up with a forced air ceiling mount, larger than needed to heat quickly when I need to use the garage. I don't heat if I'm not out there.

[Cheers]

My boiler needed to be on a platform a few feet up off the ground in order to meet code in my garage.

[rl_sd]

32 minutes ago, Grainbelt said:

I had purchased a used 80k btu house furnace for my garage only to find out it was against code to put in there. Combustible fumes at floor level was the reason why. I sure liked the radiant tube heaters but did not have enough height to install. They heat the objects in the garage, and can bake paint on the car if installed too low. I ended up with a forced air ceiling mount, larger than needed to heat quickly when I need to use the garage. I don't heat if I'm not out there.

hmmmmm..... I may need to do some checking on codes.

[rundrave]

1 hour ago, rl_sd said:

hmmmmm..... I may need to do some checking on codes.

 

I would consult your home owners insurance agent also. I know my garage had some restrictions also in terms of what they would cover in terms of heat source. I cant remember what they all were but would be something to check on also with what your policy covers.

Edited March 12, 2020 by rundrave

[ozzie]

Usually your home insurance will worry if you have a solid fuel device such as a wood stove or a pellet stove to heat the garage but it is always a good idea to check with your agent for your policy coverage and verify that you are not causing a coverage issue.

[rl_sd]

I did some checking... Having it detached makes a difference. They stated that it should be 18" off the ground, so I am going to install it on top of a cold return box

 

[Tom7227]

I have an attached 23 X 33 garage with a spancrete ceiling.  I put in a gas furnace about 10 years ago and it has a simple plenum that sits atop the furnace and only puts the heat out in one direction about 4 feet above the ground.  The garage stays above freezing without the furnace being on.  When I want to warm it up I turn the furnace on and in 2-3 hours it is comfortable.  But the heat stratifies and so it a problem.  With your 10 foot ceiling you may have a problem.  Couple of ceiling fans might help out a lot.  But as Delchecci pointed out the contents of the building are a big heat sink and will take a long time to warm up.

 

One think that I was wondering about was whether having the garage warm in the winter would accelerate the rust of my truck due to the salt.  I guess I don't really know the answer and maybe that's just the price of this type of setup.

[rl_sd]

Thanks Tom. I am sure that recover will be any issue after pulling in a cold vehicle, but I would have the same problem no matter what fan forced unit I went with. Radiant heat would be a little better and in-floor would be the best. If the house unit was purely for heat, I would probably be going a different direction... but since I also plan on having AC in the garage, this was my best choice for two birds w/ one stone at a reasonable cost