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Old 01-06-2012, 11:41 AM   #1
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wrong size furnace installed -


we closed on our new home 12/6 - 3 weeks prior to closing the oil heater croaked and the former owners had it replaced. We are in the process of getting bids for all the work we'd like to do on the home and since we're considering converting to propane we've had a few contractors in for quotes; it was brought to our attention that the furnace we inherited has a max cooling capability of 3 tons - we have a 4 ton condensing unit.
how big of a problem is this?
what should I expect the contrator who installed it do about this (if anything)?
any input or info would be appreciated.

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Old 01-06-2012, 11:43 AM   #2
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wrong size furnace installed -


Huge problem. It won't move enough air thru the coil in the furnace and it will freeze up and slug liquid freon to the outdoor unit and wreck it. Need the proper size furnace.

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Old 01-06-2012, 11:49 AM   #3
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wrong size furnace installed -


Thanks Yuri.
what should I expect the contractor to do about this when I call him about it? what would be the fair and proper thing for him to do?
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Old 01-06-2012, 11:54 AM   #4
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wrong size furnace installed -


Before you do anything,its time to have a manuel "J" and a manuel"D" done.Its quite possible (even provable) that you only need a 3 ton a/c.
Get it done even if they charge you for it,its could be the best thing you ever do concerning the house you live in.
I've been in the HVAC biusiness for more than 30 years and my experience is that older equipment is roughly 30% bigger than it needs to be in a lot of cases.
Having equipment that is too big cost you extra every time the unit comes on and after 20 years that amounts to thousands of dollars needlessly spent.
It might also show you that if you invest in insulation and/or windows the saving could be even more if you needed a furnace that was even smaller.
Of course if you are rich and spending thousands of dollars more than you need to is not a problem,then just ignore my suggestion.
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Old 01-06-2012, 12:06 PM   #5
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wrong size furnace installed -


the insulation is good - there was an energy audit done by the former owner. the windows are newer.
can I presume based on what you wrote that the contractor would be able to tell me why he put in a smaller furnace than the condensing unit calls for?
if not what should I expect as a fair remedy for this?
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Old 01-06-2012, 12:14 PM   #6
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wrong size furnace installed -


Quote:
Originally Posted by REP View Post
Before you do anything,its time to have a manuel "J" and a manuel"D" done.Its quite possible (even provable) that you only need a 3 ton a/c.
Get it done even if they charge you for it,its could be the best thing you ever do concerning the house you live in.
I've been in the HVAC biusiness for more than 30 years and my experience is that older equipment is roughly 30% bigger than it needs to be in a lot of cases.
Having equipment that is too big cost you extra every time the unit comes on and after 20 years that amounts to thousands of dollars needlessly spent.
It might also show you that if you invest in insulation and/or windows the saving could be even more if you needed a furnace that was even smaller.
Of course if you are rich and spending thousands of dollars more than you need to is not a problem,then just ignore my suggestion.
The size of the furnace "drive" is determined by the blower wheel and motor. To make your furnace a 4 ton drive it could be as easy as changing out the motor and wheel, providing it will all fit in the exsisting housing, so lets say $50 bucks for a wheel and maybe $150 for the motor.....Rep is correct in suggesting a J be done, then you will know exactly what you need for your house,the bad part is lets say the J says you need 117,000 btu's of heat and 39,000 for cooling......The don't sell units that size, you would have to get a 125,000 btu furnace and a 48,000 condensor, or go the other way and get a 100,000 btu furnace 3 ton a/c. So I ask is it money well spent?
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Old 01-06-2012, 12:23 PM   #7
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wrong size furnace installed -


Get a heat load calc done, DIY it is cheap and worth the $$. If you are converting to Propane then get the right sized furnace and sell the new oil one on E-bay and eliminate the fight/hassle with the contractor. If the AC is old (post model and serial # and brand and we can age it 4 U) then you may be better off with a properly sized new furnace and AC pkg as it will be a lot more efficient in the long run. Hard to prove in court what he should do as maybe the old oil unit was undersized also? Gets to be a he said/she said affair and you don't want to get lawyers involved at $200/hr and hire expert witnesses etc.
Load Calculator

Very rarely can the blower size be increased as the fan housing only fits one size wheel and the actual furnace cabinet needs to be larger etc.

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Last edited by yuri; 01-06-2012 at 12:31 PM.
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