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New heating and air conditioning system crawlspace installation

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Our home is 30 yrs old. We have gas forced hot air system. We need to replace the furnace and air condioning system. Our furnace is in our crawl space. It is not a dirt crawl space but rather a concrete area attached from our garage. You have to crawl through a small door, but after that it is almost high enough to kind of walk hunched over, if that makes any sense? Its not a dirt, low crawl space.

The unit is horizontal. We were told by 3 differant companie, the gas co, Sears, and a family owned local buisness that they do not make horizontal units anymore. You use a vertical one and lay it flat. All three said there are 2 types of furnaces available, 80% efficiant and 95% efficiant.

They said the 95% ones have to be vented out of the house, not through the chimmney because of the water that they produce. They said the way our house is lId out, they would have to vent it out on our deck which would mean there would be water coming out on our deck!

Only the 80% efficiant ones can be vented through our existing chimmney. We would have to put a liner in the chimmney because it is a masonary chimmney. We are confused as to what to do. We don't want to deal with water issues and pumps to pump out water caused by the furnace.

2 of the three companies said not to put the 95% furnace in. The gas co, who is the cheapest, is pushing us to put in the 95% furnace because they said for what it is going to cost us to line the chimmney, we could put in the high efficiancy for the same price. We would appreciate any suggestions or opinions you have. Vicki
asked in Heating and AC by vlapinta (120 points)
edited by darekrudy
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1 Answer

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Hi Vicki,

The contractors are correct; some time ago furnace manufacturers stopped making horizontal type furnaces and use regular type (sometimes they require simple conversion) for horizontal installations. 
 
The regular 80% AFUE efficiency furnaces require traditional chimney for venting, high efficiency furnaces which have 90% + AFUE efficiency (depends on their manufacturer) use PVC vent pipes for ventilation which can go through the side wall or through the roof.
 
The chimney can be used only as a chase for those PVC vent pipes and only if there’s nothing else venting into it anymore (a water heater, gas fireplace, etc). Also, for the PVC pipe to be installed inside the chimney it would have to be straight / not a corbelled (angled) type chimney.
 
Regular type gas furnaces cannot be vented into an unlined chimney, so if you are replacing your furnace with 80% efficiency appliance, the chimney must be updated to the current standards (lined). As for the PVC vent pipe terminating above the deck, I don’t know if this is the only possible location. 
 
There are several restrictions guarding vent pipe installations (so maybe the above your deck is the only available spot) and there will be condensation developing at the exhaust end of the pipe which will most likely cause deck discoloration because it is slightly acidic.
 
However, the vent pipe should be sloped towards the furnace so the most of the condensation will be discharged at the furnace’s end; there must be a floor drain / sump pump nearby, or a small pump installed to remove condensate from the appliance.
 
One more thing about the chimney; if you have a water heater venting into it as well and you decide to go with a high efficiency furnace, the chimney might become too large (in diameter) to serve this single appliance only and still require new liner (WH cannot be vented into an unlined chimney anyway).
 
I don’t know the layout of your house so I can’t really suggest much, let me know if my explanation triggered additional questions, just click “comment” below.
answered by darekrudy (21,730 points)
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