Another heating question

You know the fall air is getting crisp when the questions about heating the shop come out.
IDAGS on some garage heating options, with the nod seeming to go to the Hot Dawg and Reznor units. While installing my new water heater today with the help of my next-door neighbor (a plumber/HVAC guy), I asked him if he knew anything about these particular models. He didn't, and I explained how the Reznor model I was looking at uses outside air for combustion. I'm not so worried about exploding dust as I am about the precat lacquer I intend to spray. He said that any 90% efficient furnace uses outside air for combustion and that the combustion chamber is completely sealed. He could get me a great deal on a small Carrier unit (by small he means only 80K BTU...I've got him looking for something in the 45K range). Does anyone know of a reason I couldn't use a setup like this? I suspect the size will be somewhat larger than a Reznor, but I can live with that.
todd
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if a 45K Btu unit was appropriate for your space the 80K unit will be way overkill and be less efficient over all. I did exactly what you did and found that it ran more frequently for a shorter burn each time. The short burn time caused the burner assembly to rust prematurely YMMV
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FWIW I have a 90%+ efficient Trane furance and it does NOT use outside air for combustion. It is designed to be used in a ventilated furnace room or closet. It does have the low temperature condensing exhaust flue. I can look right at the flames so its not sealed.

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Perhaps I read a bit too much into his comment. It's possible that he was talking about the particular Carrier units he works with.
todd

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On 26 Sep 2003 06:19:10 -0700, snipped-for-privacy@quadnet.net (Howard) pixelated:

My 96% efficient Carrier Infinity (6 freakin' grand installed with a/c...oh, my heart) is set up the same way. It's in the attic which is already considered to be vented. It really blew me away when I saw them cut the PVC pipe to use as the chimney vent. The furnace is so efficient, I can put my hand on the chimney pipe when it's running and not get burned. It's not even uncomfortably warm! Amazing. It's also $80/mo cheaper to run than the old oil-filled baseboard electric heaters.
I would think that, for most shops with insulated walls/ceilings, the normal wall-mounted gas heater would provide enough heat. Just blow the sawdust out of it every once in awhile.
-- Music washes away from the soul the dust of everyday life. ---- --Unknown
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they work fine and the dust burns out. :-0 Actually I blow mine out at the beginning of the season and it smells a little funny the first time it comes on but it is fine the rest of the season. works quick, no splosions.
Larry Jaques wrote:

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(Howard)

My garage isn't insulated, but I don't expect to be spending loads of time out there. It's just that when I do, I don't want icicles forming on the end of my nose like last year. If you're like me, you were thinking "6 grand...why I could buy a Unisaw and a nice bandsaw and ...". From talking to my neighbor, there's a LOT of markup on that stuff. He told me that in a typical installation they run PVC to the outside for the combustion air as well. With your attic install, that might have been unnecessary. I tried a radiant unit from BORG (not that one, the other one) last year and I was underwhelmed.
todd
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will
One thing to consider is condensation. All 90+ furnaces produce condensation from combustion that needs to be drained somewhere. Also consider that you will need to run the heat 24/7 in your shop with a 90+ furnace. if you shut it off the condensate lines freeze and may break, or at least the condensate in the furnace will freeze, and render the furnace inoperable until you get it thawed out. Try do that without heat!
I considered a 90+ furnace for my shop, but the condensate drainage and not knowing for sure if I wanted to heat it 24/7 convinced me that a 80% unit was fine. I went with a conventional home style furnace because I also added central AC in the shop. Greg
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