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  1. #1
    Join Date
    Sep 2009
    Location
    Lancaster, PA
    Posts
    2

    Choice between 2 or 3 ton 2 stage vs. variable

    Hi all.
    My family (wife & son & dogs) recently moved into an existing 1700 Sq. Ft. rancher (built 1980) at the end of June. We live in central PA. We knew the existing heat pump was old but we hoped to get one or two years out of it.

    Two weeks later the heat pump failed when we attempted to start the air conditioning. The home warranty that came with the purchase of the house has covered everything up to this point. They sent out service techs about 7 or 8 times and each time the unit would work for about a day then crap out. They replaced the compressor and that lasted about 3 weeks. Finally one of the techs finally said the coil was bad and the air handler needed to be replaced. The issue was that the previous homeowner had a local company install a 2.5 ton Lennox condensor mated to a Rheem A-coil and stuck inside the original Westinghouse air handler from when the house was built. Of course the Home Warranty company just wants to slap the cheapest air handler in to replace it, but I'm feed up with the situation and I'm planning to replace the entire unit. It's one thing not to have air all summer, but another thing entirely in January. My plan all along since moving into the house was to get a home energy audit, and upgrade the insulation, seal the air gaps, replace doors and windows as needed over the next several years, mostly as DIY projects, so that when the time came to replace the old Heat Pump, we could hopefully go with a smaller size. But since our unit crapped out, I have to go ahead and replace the unit now.

    I did have a home energy audit done, and the results for the blower door were:1,870 CFM @ 50 pascals.
    The heating load was 21,581 Btu/Hr., with the required heating equipment output capacity to be 38,153 Btu/Hr.
    The cooling load was 20,844 Btu/Hr., with the required cooling equipment output capacity to be 24,513.

    Based on these results the auditor recommended sealing all the air leaks in the house (sill plate, outlets, plumbing penetrations, etc.) which he thought would bring the leakage down to around 1,404 CFM or better. (He said if we went tighter we would need an ERV or HRV system installed). He also re-ran all the load calcuations based on the tighter house with upgrading our existing insulation from R30 to R49 as well as sealing all the metal duct work, increasing the floor insulation in our unfinished basement from R12 to R30 as well as upgrading the rim joint insulation.

    The new load numbers with improvements were:
    The heating load would be 17,373 Btu/Hr., with the required heating equipment output capacity to be 28,932 Btu/Hr.
    The cooling load would be 18,967 Btu/Hr., with the required cooling equipment output capacity to be 23,941 Btu/Hr.

    So with all that said (sorry this is long), here's where I'm at:

    I plan to do much of the improvements myself to upgrade the insulation, windows, doors, air sealing, etc. over the course of the next couple years as money and time are available.

    I've had about 6 or 7 quotes from local HVAC guys regarding replacing my unit. Some of the good guys actually measured the house and duct work and did some calculations, others just looked at the existing unit and said you need 2.5 tons. I actually had one guy tell me "sometimes we guess right, sometimes not" when I asked him how he calculates the equipment size, and specifically the size for the geothermal loops! I immedialty threw out anyone who didn't do some type of load calcuation. I also had everyone quote a Mid and High end Air-Source unit as well as a Geothermal unit. At first I was pretty sure I wanted to go Geothermal, but then reality sunk in, and it's just too much to put out at this time, since we just moved into the home. On paper it makes lots of sense, and the numbers show it's the way to go, but I can't do it.

    So I've narrowed it down to 2 high end air-source units: the Carrier Infinity system and the Maytag IQ drive. I feel very good about both contractors and I feel either of them could do the job. They both think a 3-ton unit is the correct size for the house. I've explained to both of them my desire to improve my home over the next couple years and they both said that a 2-ton unit could do the job in the future. However, neither one recommends it since the house isn't actually that tight yet. They both think the 2 ton unit will struggle until the house is updated.

    So, which unit would be better? I really don't want to spend the money on a unit that will be too large in a few years. Price wise they are both comparable, the Maytag warranty is 2 years longer than the Carrier.

    Here's the specs on the units:

    Carrier Infinity 3-Ton: 25HNA936 compressor with FE4ANF006 rated at 18.2 SEER / 13.5 EER / 9.5 HSPF. The Infinity is a 2 stage with the first stage rating of the unit is 25,800 BTU.

    Maytage IQ 3-Ton: PSH4BI036K compressor with PAH4VME36KB rated at 21 SEER / 13.00 EER / 9.6 HSPF. The IQ is a variable speed which can run from 40% to 118% capacity.

  2. #2
    Join Date
    Nov 2008
    Location
    Chapel Hill, NC
    Posts
    1,070
    You should be able to seal the air leaks yourself in a weekend. Have the installing company add the attic insulation (you can probably hold off on increasing the floor insulation) and seal the ductwork. Then get a 2 ton unit - your old HP was probably not giving you anywhere near 2.5 tons of cooling/heating. If you can't or don't want to do that, then you could get a 2 stage (3 ton/2 ton) HP which should cover both bases.

  3. #3
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,368
    I wouldn't want a 2-stage unit that could potentially be oversized in stage 1 later down the road when you make the improvements. Carrier has a 25HNA636 that runs at approximately 1.5 tons on first stage (nominally 18,000 btu's) - this is the 3 ton "Infinity 16."

    Are you only looking at top-end, 2-stage units?

  4. #4
    Join Date
    Sep 2009
    Location
    Lancaster, PA
    Posts
    2
    You should be able to seal the air leaks yourself in a weekend. Have the installing company add the attic insulation (you can probably hold off on increasing the floor insulation) and seal the ductwork.
    I was planning on sealing the air leaks over the next couple weekends since it's a minor expense. I wasn't aware that any HVAC company would install attic insulation also.
    If you can't or don't want to do that, then you could get a 2 stage (3 ton/2 ton) HP which should cover both bases.
    That was my thinking that a 2 stage unit would cover both sizes, or the variable speed Maytag would get down to about 14,000 BTUs at 40% capacity.
    Are you only looking at top-end, 2-stage units?
    I was because I assumed most of the 2 stage units are on the upper end, but I'm open to other options.

  5. #5

    Carrier Infinity series set up question

    I have obtained several estimates and am concerned because each company quoted a different residential set up, I have decided on a contractor and wanted to get an independent opinion as to whether the units will be compatible one with the other, in other words, if it makes sense….

    Outdoor heat pump unit: Infinity 19 Series’ 2-Stage hi-eff. heat pump, mod.# 25HNA936A0031

    Indoor coil unit: Carrier hi-eff. 4 -ton coil # CNPVP4821ATA

    Furnace: Infinity 80’ V. Speed 2-Stage 58CVA090-f-1-16

    My house is 17 years old and pretty tight, it will be heating just the basement and first floor, the second floor has a new heat pump from 2 years ago...

    If anyone can please offer an educated opinion I would appreciate it.

    Incidentally, after all rebates (carrier and feds my cost will be $)

    Thanks.
    Last edited by beenthere; 09-27-2009 at 08:50 PM. Reason: Removed price

  6. #6
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,368
    It's a good, compatible match, and does qualify for the tax credit. You'll have to remove the price added at the end of the post since it violates site rules, but I'd say you're getting a good deal all things considered. Hope you found the right company, that's the most important thing.

  7. #7

    Thanks

    I agree that the installer is the most important, I decided to go with a company that installs more infinity series units than any one HVAC company in the USA, furthermore they also have a very high rating from Carrier as they have their presidential award.

    We had a tough time deciding because we liked the other companies giving quotes better... but this company seemed very reputable and professional..

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