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  1. #1

    Some say 2.0 ton Heat Pump others say 2.5 ton

    Hello,

    I'm getting bids on replacing my old 2.5 ton central a/c with 80K (about this number, don't remember exactly) BTU propane heat. The old unit is about 15 years old and gave up the ghost last year. The wife (just got married) is not liking the space heater so I've called some local HVAC contractors for bids.

    Here is where I'm confused: Two contractors are replacing with a 2.5 ton heat pump with 10 kw resistive heat. A third is quoting a 2.0 ton heat pump with 8 kw resistive heat.

    What is causing the confusion is that, while the window units were running this summer and the electric space heater this winter, I researched and did a manual J using HVAC-Calc. Using the design loads for Decatur, Alabama (north AL) of:

    Outdoor:
    Summer: 93 F
    Winter: 16 F
    Summer grains of moisture: 98

    Indoor:
    Summer: 72 F
    Winter: 70 F

    Heat Loss: 25,355 BTU
    Heat Gain: 13,381 BTU

    Called the local Building Department and got:
    Winter Design dry bulb: 16 F
    Summer Design dry bulb: 93/74 F
    Summer Design wet bulb: 77 F
    Degree days heating: 3323
    Degree days cooling: 1651
    Climate Zone: 8

    My home is 15 years old, 1410 sq ft, "normal" air infilteration, windows protected by 5 ft over hang (porches), dbl pane windows and low % of fenestration (84 sq ft total window), duct work in attic.

    Rising the winter indoor temperature to 73 F, the heat loss is 36,500 BTU. The T'stat will, more than likely, be set between 70 - 73 F in the winter.

    When I bought the house the HVAC system worked so poorly, a Janitrol, that I do not feel conformable using it as a gauge for the new equipment size. The two window units are rated at 5000 and 10,000 BTU. The heater is 4000 watts. The windos ac's do not keep up on the hottest days but dehumdify so much that it feels ok (about 74-76 F). The heater has done wonderful, keeping the house at 73 F at all times.

    Anyway, I thought I had done all my homework but one of the 2.5 ton contractor guys is saying that 2.0 tons will not have enough "air flow" for 1400 sq ft. He is sizing his equipment based on sq ft and air flow. This sounds reasonable, but doing search on this board says this is not the wisest thing to do.

    What gives? Who to trust/believe with this much $$$ on the line? Is my house big enough to even worry over 0.5 ton? One of the 2.5 ton contractors has been in business for +30 years and I was in high school with one of his sons, so I know the family.

    Thanks,
    JoJo

  2. #2
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    "Anyway, I thought I had done all my homework but one of the 2.5 ton contractor guys is saying that 2.0 tons will not have enough "air flow" for 1400 sq ft. He is sizing his equipment based on sq ft and air flow. This sounds reasonable, but doing search on this board says this is not the wisest thing to do.'

    Not only wierd,just plan wrong.Ask him how two stage heating and cooling systems work on low stage ,with as low as half the high stage air flow!!

    I'd ask the guy that says 2 ton,to gaurantee the deisn temperatures indoors,will be met at the design outdoor temps.,just to give you some assurance he knows what he's doing.

    Very few contractors undersize systems,but oversizing is common.

    The guy with 30 years experience,may have 30 years of doing it wrong.


    What is the R value of your attic insulation.

  3. #3
    [QUOTE=dash;1711738
    >SNIP<
    Not only wierd,just plan wrong.Ask him how two stage heating and cooling systems work on low stage ,with as low as half the high stage air flow!!

    I'd ask the guy that says 2 ton,to gaurantee the deisn temperatures indoors,will be met at the design outdoor temps.,just to give you some assurance he knows what he's doing.
    >SNIP<

    What is the R value of your attic insulation.[/QUOTE]

    Hey dash,

    Thanks for the reply. My attic is blown cellulose, the card at the access says R-19. The walls are R-11 with 0.5" blue board and vinyl siding.

    I would hate to ask the question because he could give any answer and all I could do is look at him . I don't know the answer myself. It took a few weeks to figure out the manual j. I wanted to be prepared but this is complex and I did not anticipate the different sizes.

    The 2 ton guy used a tape measure on the exterior of my home and his quote took a day to get, he may just have a smaller company but seemed to know what he was doing.

    Since I will be at this house for a few more years and energy is on the way up. And even if its on the quote, getting someone to live up to it could be difficult. The price difference is not that much up front but operating costs have me thinking.

    Does the 2 ton sound reasonable? Will the reduced cfm's (from 2.5 to 2.0 ton)at the registers be noticed?

    Thanks again,
    JoJo

  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,043
    With those kind of heat gain/loss numbers, 2.5 ton (over double the heat gain) is unreasonable. Do you want humidity control or not? The big unit not running much won't dehumidify like the smaller unit with longer run times.

    As for airflow, I don't think you'll miss 200 CFM spread out over all the registers. You tend to get more even heating & cooling with a smaller unit running more. Reminds me of a sale 15 years ago when I was a rookie. Guy with big 2 story house and 3 ton wanted bigger to better cool the upstairs. I put in a 2.5 ton instead of going bigger. He admitted the house was more comfy due to the longer run times evening out the temps and the better dehumidification of less frequent cycling.

  5. #5
    Join Date
    Jan 2002
    Location
    East Grand Forks, MN
    Posts
    1,373
    Since I will be at this house for a few more years and energy is on the way up. And even if its on the quote, getting someone to live up to it could be difficult. The price difference is not that much up front but operating costs have me thinking.

    Does the 2 ton sound reasonable? Will the reduced cfm's (from 2.5 to 2.0 ton)at the registers be noticed?
    I haven't done a load calc. But 1400 sq ft in your region looks like a 2-ton is a good choice. I haven't looked at the cooling specs of your equipment either, but a 2-ton might the correct size. Yet again, I will reiterate, without a proper loadcalc and equipment selection you as the customer and the contractor take a chance of installing a low performance system. It seems you are looking for a high performance system; low operating cost and you want to be comfortable at the same time.

    800 cfm's could be correct for your house (heat load). If the duct system is installed correctly, you need not worry about enough or adequate airflow!!

  6. #6
    Join Date
    Dec 2007
    Location
    oregon
    Posts
    885

    Wink

    I would install the 2 ton if your load calc numbers are right. Longer run times are desirable in the summer for better humidity control. Drier air feels cooler. I did a project on a 2 story house that was 3200 square foot. we installed a 3 ton dual capacity Trane xl19i a/c system with two zones. I did a load calc and went by the gain/loss numbers that the program came up with. All the other contractors were bidding 5 ton units. I offered to guarantee the performance based on the indoor temps he provided me at the time I did the load calcs. It has been over 3 years and he is very happy and comfortable in his home. Go with the guy that does a proper load calc and ask him to show the report to you and explain it. We do a load calc on EVERY job.
    Good luck!

  7. #7
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    Here are the phrases to run from. "Seems like...", "Sounds like....", "I think....", "....Square Feet....", "...30-years...", "...so much experience...", "...trust me...". All of these are actually saying "I have not done a Manual 'J' calculation so I'm guessing."

    If you trust the Manual 'J' calculation, as long as the proper numbers have been fed in, you've got all but a written guarantee that sizing the equipment accordingly will give you the best result financially at purchase, financially over the operating long run and comfort wise. If you want least expensive operation over the years, then select a 2-stage unit with a variable speed air handler that will have sufficient capacity to heat the home without "toasters", yet won't be oversized for the cooling season. Put the resistance heaters in for emergency use or sub-normal heating purposes but plan on using the heat pump right down to design temperature. These days a heat pump can beat the electric resistance heaters on cost of operation right down to 2 to 4 degrees above zero. So if you need 2-tons for heating down to 16*F, buy a 2-ton, 2-stage heat pump and if that isn't available in the model/color/country of origin of your choice, put in a 3-ton, 2-stage unit. You'll still be covered, though the up front cost will be slight morre and the efficiency could suffer some. But you'd have plenty of push for the cold weather and still wouldn't be grossly oversized on first stage in the summer. Just be sure your distribution system can handle a bigger unit if you go that way, not that I'm recommending it if you don't have to.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  8. #8
    Join Date
    Dec 2007
    Location
    oregon
    Posts
    885
    Amen mr skipped over! The two stage unit will save you money in energy costs if it is properly applied. If a contractor will guarantee his work and give you references, go with him.
    Genius = The guy who can do anything...except make a living!

  9. #9
    Join Date
    Jun 2006
    Location
    Hastings, MN
    Posts
    417
    Could be as simple as Carrier Infinity only uses 2 ton and then jumps to 3 ton no .5 tons . Trust manual J
    Aint Notin Sweeter, Then A Brand New Heater!!!!!!!!!!

  10. #10
    Quote Originally Posted by skippedover View Post
    >SNIP<
    If you want least expensive operation over the years, then select a 2-stage unit with a variable speed air handler that will have sufficient capacity to heat the home without "toasters", yet won't be oversized for the cooling season. Put the resistance heaters in for emergency use or sub-normal heating purposes but plan on using the heat pump right down to design temperature. These days a heat pump can beat the electric resistance heaters on cost of operation right down to 2 to 4 degrees above zero. So if you need 2-tons for heating down to 16*F, buy a 2-ton, 2-stage heat pump and if that isn't available in the model/color/country of origin of your choice, put in a 3-ton, 2-stage unit. You'll still be covered, though the up front cost will be slight morre and the efficiency could suffer some. But you'd have plenty of push for the cold weather and still wouldn't be grossly oversized on first stage in the summer. Just be sure your distribution system can handle a bigger unit if you go that way, not that I'm recommending it if you don't have to.
    Wow! Thanks for all the great pointers. Yes, long term $$$ is important to me, more than the up front.

    OK, now I have better questions and a better idea if what I want/need.

    Thanks Again,
    JoJo

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    Do you really want a system to be installed by a guy who multiplied 1400 x .7 to come up with 980CFM to determine what size unit you need?
    Contractor locator map

    How-to-apply-for-Professional

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

  12. #12
    Join Date
    Jan 2007
    Location
    Minneapolis, MN
    Posts
    415
    I would add that for long term comfort success that you have a blower door and duct blaster test to make sure the building envelope and duct work are sealed properly and make needed improvements. Your heat calc assume tight ducts and you are guessing at the infiltration rate. I was playing with some numbers and your load could be reduced by 3k to 5k btu depending on infiltration and duct gains and losses. My guess is that your house is leaky by the age of the house and the ducts located in the attic. I also agree on 2 ton 2 stage.

  13. #13
    Join Date
    Dec 2007
    Location
    oregon
    Posts
    885
    A duct blaster and blowerdoor test to determine the integrity of the building envelope and the duct system will tell all. It takes less then 2 hours to perform ( in most cases) and will reveal alot. Have a independent tester do the test if the contracters in your area don't do them. In Oregon on exsitng homes for a home owner to get tax incentives and or utility rebates we MUST do them. We have been doing them for over three years and it is amazing what you can learn about a home and the ducts. We now do them as part of our retro bids, and we end up with alot of one call closes because no one else wants to do them!
    Genius = The guy who can do anything...except make a living!

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