Ebay question for you guys. I have a furnace that I’m trying to sell on ebay. Here’s the link: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5921739217 A buyer has contacted me and asked if this furnace would be large enough to heat her home. She lives in Cleveland, Ohio and her house is 1100 square feet. I’m thinking that the furnace might be a bit small (75,000btu/96%), but I’d sure hate to lose the sale on my guess. What do you guys think?
Certified boat fetish.
Edited 9/22/2004 10:05 am ET by Timbo
Replies
If the cleveland house is reasonably insulated, 75 K btu is oversized. I have a 50 k unit w/ same climate as OH heating 2200 SF.
Since you say this furnace is a 75K OUTPUT, then at 95 %, the OUTPUT would be approx 70 K. IMO, 70,000 output will still adequately service a 1100 sq ft (plus a couple of basement runs too) home, provided there is an AVERAGE level of insulation,fairly good windows etc. Smaller is better when it comes to heating and cooling.It eliminates "short cycles" etc., in both heating and cooling modes.
>>Since you say this furnace is a 75K OUTPUT, then at 95 %, the OUTPUT would be approx 70 K.
FWIW, I just finished a combustion analysis course today with Jim Davis of NCI. According to Jim, the "90+" furnaces don't come anywhere near 90% efficiency, even when perfectly tuned, and few are properly tuned, according to him. My notes are still out in the car, and I don't remember the figures or formulas he gave, though.
Oversizing is a problem with A/C because of the lack of adequate dehumidification; I'm not sure that you have the same issues with oversized furnaces though, aside from some additional wear and tear from ignition.
I have heard it said that the condensing type furnaces have their highest efficient during the early part of the heating cycle, and thus short cycling would be advantageous, but I don't know if that is accurate.
Sojourners: Christians for Justice and Peace
"I'm not sure that you have the same issues with oversized furnaces though, aside from some additional wear and tear from ignition."
The basic problem is big temp swings.
My 1st floor furance is about 3-4 times oversized based on the percentage of run time when it gets down to about zero.
I think that the only reason that it "works" is that I have ducts in the slab. And while it is not radiant heat the slab picks up enough heat and is a large thermomast to temper the swings.
Yep, probably oversized if the house is reasonably insulated. Our house in southern MN has two 75K input furnaces with ca 60% efficiency, and we could easily heat the house with only one -- two are used for zoning. House in 1976 construction with 2x4 fiberglass-insulated walls (though we've tightened up the construction a bit with housewrap, et al). Our total SF is around 2000, but it's a split-entry with the bottom floor half-buried, so the "exposed" SF is probably equivalent to about 1200-1500.
It would be super difficult to guess the heatloss numbers from afar. So many variables.
You could point the buyer to this free heatloss calc program:
http://www.slantfin.com/hydronic/index.html
Well, the house is a 50's ranch. It's proably not that well insulated. I don't know if the windows have been replaced or not. Either way, it seems as if this furnace would meet her needs. Thanks for your help guys.
Certified boat fetish.
If properly tuned, a 75,000btu 90+ should be fine for 50's ranch in Cleveland.
That is not a common brand sold in this area (at least in NW ohio) and I've only seen one similar furnace with that draft inducer.
She might want to call around to see if there is anyone in her area who can install and service it.
Sojourners: Christians for Justice and Peace