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  1. #1

    Questions on a Hybrid System

    I'm a first-timer here, so bear with me.

    We live on a windy mountainside in Western North Carolina, and I want to replace a propane furnace and electric air conditioner with a heat pump and a propane furnace. I've gotten three estimates that have left me comparing apples and oranges. Only one contractor has done anything approaching a Manual J heat calculation, but one of the others says he'll do one after I sign a contract and before he brings the equipment.

    All three estimates treat the heat pump as an add-on to the propane furnace, and I think it ought to be the other way around. Two of the three are proposing 92% AFUE two-stage, variable speed furnaces; the third is proposing a 92% AFUE one-stage, single-speed, but it appears to be a builder's model.

    All are quoting 13 SEER heat pumps, but one also is offering a 15 SEER HP for only about $300 more. I could get that difference back from the 2009 federal tax rebate.

    What I'm proposing to do is to ask all three to give me estimates on a 15 SEER, 9 HSPF HP, which qualifies for the federal rebate, and a 92% one-stage furnace. My thought is that the furnace would kick in at an outside temperature (35 degrees or so) where it would have to run at or near full tilt anyhow, so the lower stage wouldn't be of much benefit.

    Does this make sense, or am I off base?

    Thanks for your input.

  2. #2
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    How can the contractor provide a quote ifhe doesn;t know what size furnace or heat pump he will provide???

    On a dual fuel/Hybrid system, the heat pump is the "primary" heat source, the propane furnace acts as the air handler and the burners are the auxillary heat source.

    I think the hybrid control on the Carrier Inifinity is very good as well as using a Honeywell IAQ with any other make/model system as second best. Mainly because during defrost, the carrier allows a delay before the defrost starts.

    For the federal rebate, it needs to be 9HSPF, 15 SEER AND...big "AND" 13 EER. Good luck findings unit to meet all 3. Plenty of them meet 9 and 15, but not the high EER. I will tell you it will cost 2-3 times above the wimpy $300 they give you. The local utilities usually give a larger rebate.

    Definitely get the 2 stage VS furnace. Size the heat pump for cooling demand and being in a warmer climate, you should have good heating performance down to 30F where you are.

    Also keep in mind that for the same price, you could get a 80% furnace and a 19 SEER A/C. You will liekly save more on you energy bills going that route, than spending money on a 90%. With a dual fuel, you're only using the furnace less than 50% of the time so teh payback is twice as long. With the higher cost of propane, the calculations could be different. You may want to crunch some numbers.

    If you can afford it, consider a 2 stage or multistage heat pump.

  3. #3
    Quote Originally Posted by motoguy128 View Post
    How can the contractor provide a quote ifhe doesn;t know what size furnace or heat pump he will provide???
    They're all quoting 100,000 BTU furnaces, because that's what we have now. One is quoting a 4-ton HP, one a 3.5 and one a 3. I think the current A/C is a 4 ton.

    A neighbor who's a building contractor this morning gave me the name of the HVAC contractor he uses, and I've got a call in to him, too.

  4. #4
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by Mountain Man View Post
    They're all quoting 100,000 BTU furnaces, because that's what we have now. One is quoting a 4-ton HP, one a 3.5 and one a 3. I think the current A/C is a 4 ton.

    A neighbor who's a building contractor this morning gave me the name of the HVAC contractor he uses, and I've got a call in to him, too.
    So they're all just guessing. Unless you KNOW what the duty cycle is of your current system at the design temperatures, you need a load calculation done.

    For example on a 95 degree humid day, does the A/C run flat out 100% of the time at a indoor temp of around 75F??? If no, it may be oversized.

    Does the current furnace run flat out of a 10F evening with a indoor temp of 70F??? If not, it's possibly oversized.

    I'm just taking guesses at the design temps for your location. Someone else on here can tell you want to use or where to locate them.

    One other thought that some disagree with, but you can oversize a 2 stage heat pump by 0.5 Tons to get a little more capacity for heating without sacrificing dehumidification in the summer.

  5. #5
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by Mountain Man View Post
    They're all quoting 100,000 BTU furnaces, because that's what we have now. One is quoting a 4-ton HP, one a 3.5 and one a 3. I think the current A/C is a 4 ton.
    My point was that the one contractor was quoting you a system, without doign a size calculation, but if you signed a contract, he would do hte calc, then change the size of a unit? Will you get a credit if the size changes? Charged more if it gets bigger?

    Would you sign a contract ot have a house built, without knowing if it would be 200, 2200 or 2400 square feet... or even what floor plan. The contractor would ahve an incentive to do whatever is most profitable... a bait and switch.

    SO lets say this guy is a lowest bid, he quoted a 80k VS unit with a 3 ton 15 SEER HP. His calculation determine you needs a 3.5 Ton and a 100k furnace. He "cuts you a deal" and get you a non VS 100k furnace and a 14 SEER HP for the same price. Is he still the cheapest quote? Too bad because you already signed a contract.

    Either way, his "contract" would be void if he proposed different equipment. I'd be concerned he'd manipulate teh numbers (not hard to do on a manual J) to make sure the size he proposed fell within the calculations.

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,765
    With those sizes.
    I would guess you have about 3600 sq ft.
    Or a lot of windows, or a really drafty house.

    Keep calling see if you can find a contractor that will do a load calc.

    If not, go HERE and do your own load calc, and find out wat size you really need.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  7. #7
    Quote Originally Posted by beenthere View Post
    With those sizes.
    I would guess you have about 3600 sq ft.
    Or a lot of windows, or a really drafty house.
    The heated square footage is 2,150. We have about 200 sq. feet of windows. The house is tight. We get wind gusts up to 60 mph in the winter, and I don't feel or hear any major air leakage sources.

    You folks are making clear that I really need to insist on a heat load calculation. I was planning to do that anyhow, but you're reinforcing my opinion.

  8. #8
    Quote Originally Posted by Mountain Man View Post
    The heated square footage is 2,150. We have about 200 sq. feet of windows. The house is tight. We get wind gusts up to 60 mph in the winter, and I don't feel or hear any major air leakage sources.

    You folks are making clear that I really need to insist on a heat load calculation. I was planning to do that anyhow, but you're reinforcing my opinion.
    What size did you end up going with?

  9. #9
    Went with Goodman: a 90,000 BTU furnace and a 3.5-ton heat pump with the appropriate coil. Don't have the model numbers at hand, but the system will qualify for the $1,500 federal stimulus tax rebate.

    I'd like to experience it in operation, but between a two-day hospital visit for surgery and today's warm weather here, I haven't had much chance to do so.

    Thanks to all here who provided guidance.

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