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My home in So Calif has its furnace on the 2nd floor (stupid). The house (built in 1983) has always had a problem with poor heat distribution to the 1st floor. The house is about 3400 sq ft total, split about evenly between 1st @ 2nd floor.
I’m possibly wanting to have a separate furnace & ductwork installed, just for the ground floor, and want to think through some options. My choices as to where to put the furance for the 1st floor are limited. There is ample crawl space. Putting the ductwork for a 2nd new ground floor furnace, in the crawl space, seems a reasonable option.
The question has to do with the furnace itself. I intend to use a furnace with sealed combustion. I do not want combustion air drawn thru the house – there are just too many small leaks & drafts thru the early 1980s era doors & windows.
First, is drawing combustion air from the ventilated crawl space code-legal? If it is legal, are there practical reasons for or against?
A second option is to put a (non-sealed combustion) furnace on a small exterior pad, right next to the house. I’ve never seen this done. Is there a reason for / against, other than just habit?
Third option, I could just leave the existing 2nd floor furnace alone, & install some kind of booster fan in the one main duct feeding the whole 1st floor, in an effort to get better ehated air distribution. This sounds like the easiest & cheapest (?), IF there are standard ways to do it – I don’t want this to become some kind of mad scientist experiment.
Would one just use a single thermostat for the whole house?
Should the booster fan be wired to always turn on, at same time the furnace fan does?
Or should a separate thermostat on the 1st floor somehow be used to turn the booster fan on/off?
Any experiences or inputs from HVAC experts, is appreciated.
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My first thought when I read your post was why is there not sufficient heat getting to all parts of the house? Was there ever enough heat? Maybe the furnace is just too old or of insufficient size to begin with. Oversized ductwork, leaky elbows and pans, the added on vent here and there,combined with a 60% efficient furnace makes for a great amount of heat loss.I'd speak to an hvac or weatherization contractor first,and maybe try to trace some possible leaks/bad connections.The crawlspace is a good place to start.Maybe replacing the exisiting furnace and ductwork with a high efficiency furnace and new ductwork would do it ? I can't tell you about any code implications of any of the installation situations you mention ,however I can tell you I have never seen a furnace(except heatpumps) outside,but I'm sure some manufacturer makes one.
*There was never sufficient heat to the 1st floor, especially the end furthest from the heater. This was so, even when the house was brand new (I am the original occupant). It appears to have been inadequate from day one; after nearly 15 years I've got tired enough of it, to want to finally correct it. It's a Rheem furnace, I vaguely recall it was somewhere in the 40-50,000 BTU range. I had the original installer check it out during the first heating season in 1984-85, not surprisingly "no trouble found", just a shrug as to why there was inadequate air & heat to the furthest ends. The only part of the ductwork (sheetmetal, not flex ducts) still easily accessible is in the attic, the rest is inside the walls. I don't doubt there are some small leaks in the ductwork, but nothing gross (like a branch that got left opened up).There is adequate heat & air to all registers in the 2nd floor. I've had to close most of them down, to get any resemblance of heat forced down to the 1st floor.I've just chalked the whole situation up to bad initial duct layout & design, and that heat wants to rise. Hence, my interest in a separate heater, or maybe a booster fan in the duct going downstairs.
*Tom,I'm not an HVAC specialist but have three thoughts to share. 1) Consulting with an HVAC specialist might be a good idea! 2) In a recent Journal of Light Construction (www.jlconline.com), it may be December's issue, there is an article on point concerning your question of drawing makeup air from a crawlspace. 3) I own a home with a furnace in the crawlspace. I'm not overly fond of this arrangement. But, it was my idea to put it there in the first place!