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Venting Q's


gmanmdg
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I have Carrier 58sta090-14 nat gas furnace. I want to use this furnace in my garage laying horizontal. My garage is a 20x20 2 car garage all drywalled. In the garage attic there is a vent for the gas clothes dryer. What i need help is on: Can I wye this vent and vent the furnace through the gas dryer vent in the roof? The vent is approx 6 to 7 ft away from a window that over looks the garage roof.

Thanks Mike

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Originally posted by gmanmdg

I have Carrier 58sta090-14 nat gas furnace. I want to use this furnace in my garage laying horizontal. My garage is a 20x20 2 car garage all drywalled. In the garage attic there is a vent for the gas clothes dryer. What i need help is on: Can I wye this vent and vent the furnace through the gas dryer vent in the roof? The vent is approx 6 to 7 ft away from a window that over looks the garage roof.

Thanks Mike

Sure, if you want to perhaps vent the furnace fumes back into the house through the dryer vent, and perhaps killing everyone in the house. (As WJ would say....mirth.)

Jerry....also in Crystal Lake, who don't want to read about such in my town.

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Originally posted by gmanmdg

Ok, Let me ask this then. Can I put it in my basement and then wye into the venting for my current furnace?

Yes, if the current vent is sized and configurated for the extra BTU's. I've got a local HVAC guy you might want to consult. Shoot me an email if interested (and you should be). jerry@illinoisbuildinginspection.com

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My only concern about installing it in the basement is that this such a big furnace designed to heat a whole house and I just want it to heat a garage. The reason I wanted to locate it in the garage was because the full output and input would be going to the garage. If I mount it in the basement, I can only fit like 2- 12x8 ducts through the floor and out into the garage for heat and 1-12x8 return duct. I am just afraid of choking the system.

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Hi,

Furnaces are located in garages all the time around here, so physically locating it in the garage isn't the issue. The issue is where you'll get your return air and combustion air and how you'll vent it.

You'll need to set it up so that your return air isn't being drawn from within 10ft. of the burners or draft hood. That means you'll need to install a return air duct that will gather air from the opposite end of the garage from the furnace.

You'll need to figure out whether there's enough combustion air in that garage for the furnace. You'll need to know the volume of the garage in cubic feet and you'll need to have 50 cubic feet for every 1,000 Btu/Hr input of the furnace. For instance, a 75,000 Btu/Hr furnace is going to need 3750 cubic feet, but a 100,000 Btu/Hr furnace will need 5,000 cubic feet. If it were a 100K Bth unit and your garage is only 20 by 20 by 10, it will be too small, so you'd then need to either cut an opening in the outside wall of the garage to allow fresh outdoor into the garage (That will only defeat the whole purpose of the furnace being installed in the garage), or you'll need to build an enclosure around the furnace to seal it off from the rest of the garage and then install a properly-sized intake vent from the outside into the furnace room so it will have sufficient combustion air.

Like Jerry said, you can't use the dryer vent, so you'll need to install a double-walled 'B' vent right up through the roof, ensuring that it's correctly sized and configured and that it extends the right height above the roof.

All of that's going to be expensive, and then that big unit is going to constantly short cycle, because it's way-oversized for the area you're trying to heat, and you'll stress the heat exchanger and waste fuel.

You can stick it in your basement if you want to, but then you've violated the membrane between the garage and the house and you'd probably need to install backdraft dampers on the system - another cost. Also, if the basement isn't large enough in volume to accommodate both of those gas appliances (the old furnace and the new one) plus any water heaters and gas dryer, you'll need to either scavenge combustion air from the rest of your house or cut in exterior vents into the basement. If it's a heated basement, guess what? Now you've got to have both furnaces in an enclosure and get their combustion air from outside.

Now do you see why Jerry is telling you to get an HVAC guy out there? This is not the type of thing one does for a do-it-yourselfer project. If I were you, I'd install a small forced-hot-air gas-burning garage heater that's sized for that 4,000 cubic foot space and drop that big furnace off at the nearest landfill. Or, if it's not too old and still in decent condition, maybe you can arrange to swap it for a small gas garage heater with a local HVAC guy.

ONE TEAM - ONE FIGHT!!!

Mike

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