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Thread: Using house furnace to heat attached garage

  1. #1
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    Default Using house furnace to heat attached garage

    Hey guys,

    I have a small (13x20), well insulated, attached garage and was wondering if running a line off my house furnace would be a good idea? Thanks

    Rob
    Last edited by robphill; 10-10-2010 at 11:08 AM.

  2. #2
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    Default Re: Using house furnace to heat attached garage

    If it's forced air then I'm not sure this is even legal.

  3. #3
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    Default Re: Using house furnace to heat attached garage

    Yes, it's forced air. I was wondering if it was legal. The more I think about it, the more it doesn't make sense. Think I will try an electric space heater.

  4. #4
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    Default Re: Using house furnace to heat attached garage

    Reason why this isn't done is because the return air duct to the house would allow fumes from a car in the garage to enter the house. I couldn't get a car into my garage right now, but some future owner migh revert to doing that, so I use electric heat there.
    Jim

  5. #5

    Default Re: Using house furnace to heat attached garage

    If you have a natural gas supply you should consider a gas radiant heater. There has been lots of discussion of this route on this forum.

    Glenn

  6. #6
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    Default Re: Using house furnace to heat attached garage

    It's not illegal if it's not a garage. If it's a shop then it's fine. I would have done it in a heartbeat at my old place if the stairwell did not get in the way. Easy enough to disconnect and seal the hole down the road if you sell.
    Paul

  7. #7
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    Default Re: Using house furnace to heat attached garage

    I have a 26 X 25 X 10ft R20 walls and ceiling. The heat of the vehicles keep it decent - the snow that falls off is water and stays water to the drain. My attached shop is 15 X 25 X 10ft ceiling. I now heat it with one of those oiled filled radiator style units. Quite cozy. If I need more I have a 4800Watt construction heater that will bring the garage up to 20C in about an hour.
    I live outside of Edmonton so do see an extended amount of -30 C weather.
    If you building is well insulated you shouldn't need continuous heat, just a good source of auxiliary heat when actually working in the garage.
    The only advantage to continuous heat i the garage is it might slow down the vehicle rusting. My garage gets warm enough to melt the snow, but not dry it out completely. The older vehicles really rusted up once we started using the garage.

    Don

  8. #8
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    Default Re: Using house furnace to heat attached garage

    I'm kind of worried about the return. One, I'm spraying wb lacquers and the fumes would get drawn into the house and furnace. Two, the return would have to be right beside the supply in my situation.

  9. #9
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    Default Re: Using house furnace to heat attached garage

    You don't need a return air. The garage will have so much natural air leakage/exchange that sucking it back in is pointless. Return air .....picture a paper bag...you blow it up (heat), without a hole at the other end ( cold air return) you have no air movement. Once the bag is full no more air will go into it. In your case the garage will leak enough to supply the exchange.
    Last edited by OttawaP; 10-10-2010 at 07:40 PM.
    Paul

  10. #10
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    Default Re: Using house furnace to heat attached garage

    Quote Originally Posted by OttawaP View Post
    You don't need a return air. The garage will have so much natural air leakage/exchange that sucking it back in is pointless. Return air .....picture a paper bag...you blow it up (heat), without a hole at the other end ( cold air return) you have no air movement. Once the bag is full no more air will go into it. In your case the garage will leak enough to supply the exchange.
    I agree with this for what is probably the most common situation out there, but in my case, this is not the case.

    My one car attached garage has been completely dedicated to being my playroom....err...shop. I've got a wooden built-up shop floor that is quite comprehensive in functionality which results in a 6 inch rise where it meets the garage door. The garage door is insulated and has been gasketted to minimize air leakage. (You can see more about the floor in my photo gallery).

    For heat - and air conditioning - I basically altered two of the six inch vents in the house to pump air into the shop. They both have one way baffles on them to prevent any excessive dust from migrating back into the ducts as well - even though I have excellent chip/dust collection and an air cleaner. If I close my door that goes from my shop to my house, there is hardly any air that would go into the shop. I therefore included a cold air return in a location that also has a 16X20 cheapo furnace filter over an opening at the rearmost of the shop, which also keeps sound migration down, that flows return air into the adjacent room, which itself has ample cold air return.

    Winter is perfect, and even when I go in there on those super cold days outside which will make the shop a little coolish, the fluorescent lights will warm to just right in 10 minutes. Summers, I often find I'm minimizing the light usage, as it can get warmish on the really hot days. So, it's not perfect, but it works pretty darn good, and I am very happy I went thru the exercise and took this route. It should be noted that the floor itself offers a great amount of insulation, and my shop walls have Reflectofoil under them, along with original insulation under that.

    I should mention I intentionally left the areas modified to vent, in a manner so that when I move, they can be quite easily be reverted back to the way it was before, and sealed sufficiently, that a future homeowner wouldn't resume using the area as a car garage, discover the vents he could too easily re-aim to heat/cool the garage, and unknowingly cause themself a carbon monoxide hazzard to themself and their family.

  11. #11
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    Default Re: Using house furnace to heat attached garage

    Quote Originally Posted by OttawaP View Post
    It's not illegal if it's not a garage. If it's a shop then it's fine.
    Whether you do woodworking, grow marijuana or have a dance club in your garage it's still a garage according to your municipal records.

    In my first post I kinda lied a little by saying "I'm not sure it's even legal". Actually I am pretty sure it is not legal as per Ontario building code. I had that very same idea last Winter so I asked a building inspector and later a chief building official (kinda uber inspector). I explained how I would install filters, one way dumpers etc. Both said without a moment of hesitation that it is definitely not legal unless the designation of the garage is officially changed to a woodworking shop.

    That is not a trivial matter if the house is in a residential area. In such case a city/town planner needs to be involved since zoning bylaws come to play. The planner didn't give me a straight answer since he doesn't know relevant by-laws for St. Catharines. His opinion was a mild "you're unlikely to get minor variance for that".

    And if this is not enough the fire Department may have to be involved too. A lot of paper work needs to be shuffled, a few dollars need to change hands and in the end the change of the zoning, and Fire Department's approval are a thin chance. I asked the fire chief about that too. His answer was (and that's a quote) "absolutely not", followed by a bunch of safety/health reasons.

    Of course, you don't need to go through all that if you don't apply for a permit to alter your heating duct installation. But then, in most municipalities in Ontario it is illegal to alter duct work without a permit.

    I ended up buying a quartz heater. Ceiling mounted. Exactly the same model a buddy of mine uses in his garage. He is the chief building inspector mentioned above.

    (btw. I work for a municipality and as an IT fella I deal with all those guys on a regular basis.)

  12. #12
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    Default Re: Using house furnace to heat attached garage

    Quote Originally Posted by darius View Post
    Whether you do woodworking, grow marijuana or have a dance club in your garage it's still a garage according to your municipal records.
    Yes and no..... I probably should not have said it's "legal" but should have said it's perfectly safe for a shop only "garage". Let's start over. If this was new construction and you wanted to heat this "garage" with duct work and use it as a garage it would be a big no no. If you wanted to heat it as a "shop" or "garage" the the insulation of the foundation would be an issue since it would need permiter insulation. If you wanted to heat it as a shop with ductwork for new construction...no problem if insulated properly. There are no temporary livable rooms allowed in a home allowing reduced insulation. Only a cottage can get away with reduced heating/insulation etc. And, technically if you put a permanent gas heater in the garage in a previously uninsulated area, then the insualtion is supposed to be upgraded with a permit to today's standard....but really, who does that...
    If you wanted to go to the city to convert your garage to a shop with a permit you could. "Change of use" permits typically apply to an entire building, for example changing an old church to a home, or a home to a private school but not always. Then, zoning and codes reqm't kick in for the different use. Now, If the city looks at your shop as a living space now, be careful you don't have a zoning and setback issues. Some cities will allow garages closer to property lines since they are not a livable area, changing it to a shop might change that and require a minor variance....yuck.
    If the shop is for professional use...good luck with the zoning, parking issues etc. There should be a section of your zoning bylaw last lists the permitted home based businesses. Hobby/personal use is not an issue.
    I was a former inspector, 13 long years (well only the last 5 were long) and while I did mostly commercial/industrial/institutional I did have an area of residential and trust me, i saw it all. Every wannebe, every pro, every cheater, every home owner over his head (I even partially framed a few roofs to help some guys along that were lost) and stuff like this is not a big deal if you want to go through the process. Personally I would just do whatever you want and feel comfortable with, and leave the city out of it unless it's for a business.
    Last edited by OttawaP; 10-11-2010 at 07:28 AM.
    Paul

  13. #13
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    Default Re: Using house furnace to heat attached garage

    But the room would not be continuously pressurized unless the furnace was set to run constantly. If the furnace cycled, it is possible that fumes and dust could find their way into the living area through the heating duct. Fumes for sure.

    Don

  14. #14
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    Default Re: Using house furnace to heat attached garage

    Quote Originally Posted by robphill View Post
    Yes, it's forced air. I was wondering if it was legal. The more I think about it, the more it doesn't make sense. Think I will try an electric space heater.
    Good plan.

    Don

  15. #15
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    Default Re: Using house furnace to heat attached garage

    It's easy to overestimate how much heat you need in your situation. I have a reasonably (1960's) insulated attached garage, 10 by 20, and all I need is one of these ; http://www.canadiantire.ca/AST/brows....jsp?locale=en
    It has 3 settings, low, high or both together, and in the 5 or six years I've had it I've never had to turn on both together. There's a bit of a draught from under the door, so I keep it near the door at the outer wall. Because I use the shop most days I keep the temp. at around 60 deg. It takes only about 15 mins. to crank it up higher. If I used the space less frequently I'd keep the setting lower, but in any case the impact on my heating bill is negligible. It has a small footprint, is moveable, and safe -- if you knock it over it won't start a fire, and it's silent. Cheap too, esp. if you get it on sale. The one drawback is that it uses a small amount of floor space, but the lower the source of heat the better, and I don't really have much spare wall or ceiling space. Why spend time and money on something you probably don't need?
    Jim

  16. #16
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    Default Re: Using house furnace to heat attached garage

    I have tried a $30 1500W electric space heater and it takes way too long to warm it up. I was planning on hooking up a 5000W (17000BTU) electric heater for around $500 (including the new circuit cost).
    The back half of my shop is a spray booth and I need to reheat the garage quickly when I have the exhaust fan on. I doubt 17000BTU will do it, but it's the only option I can think of for the price.

  17. #17
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    Default Re: Using house furnace to heat attached garage

    No you can't do it.

    Even if you can find a code loop hole you'll kill yourself if you gas one of your kids. Spend a grand and buy a radiant gas heater.

  18. #18
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    Default Re: Using house furnace to heat attached garage

    Quote Originally Posted by Rusty View Post
    Spend a grand and buy a radiant gas heater.
    Most garages aren't really high enough for a ceiling hung radiant tube to do a good job. I've heard horror stories about panels warping badly because the radiant heat dried out the top of the panel much faster than the bottom.

  19. #19
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    Default Re: Using house furnace to heat attached garage

    Quote Originally Posted by Chris in Saskatoon View Post
    Most garages aren't really high enough for a ceiling hung radiant tube to do a good job. I've heard horror stories about panels warping badly because the radiant heat dried out the top of the panel much faster than the bottom.
    Oh!!!! How high do they have to be? Maybe I should go and measure.

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