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  1. #1
    Join Date
    Nov 2007
    Posts
    13

    Heat pump lesson

    Need a lesson on heat pump outside temp versus what is possible to get as inside heat. If needed, base it on using a 3 ton 8.7hpsf 16SEER w/varspeed air handler. So if its 40 degrees F outside, what can I expect for HP inside house temp etc. i will continure googling web to learn but you are the pro's!!! Thx

  2. #2
    Join Date
    Jun 2007
    Location
    Metro St. Louis
    Posts
    181
    Quote Originally Posted by stockgal2 View Post
    Need a lesson on heat pump outside temp versus what is possible to get as inside heat. If needed, base it on using a 3 ton 8.7hpsf 16SEER w/varspeed air handler. So if its 40 degrees F outside, what can I expect for HP inside house temp etc. i will continure googling web to learn but you are the pro's!!! Thx
    Well, if you want to base it on a 3 ton 9.75 HSPF 16SEER two-stage HP, see below (pages 24-25)

    http://securenet.goodmanmfg.com/pdf/...T6214003R4.PDF

  3. #3
    Join Date
    Jul 2007
    Location
    Phoenix, AZ
    Posts
    206
    There are a lot of different things that will determine what temp the heat pump will blow out of the air registers. But at 40 degree outside temp you should see an air temp of around 100 to 130 degrees out of the supply air registers. That is if your indoor temp of the house is around 70 to 75 degrees. Kick on some back up heat strips and it will blow even hotter air. But that means more electrical use. A lot of people will shut there heat pump off at night. Here in the mild winters of phoenix. The indoor house temp goes down to 60 degrees. They get up in the morning turn on the heat pump and it takes for ever to heat the home up. You must leave the heat pump on at night. With gas heating this is not a problem. Gas heat in my opinion is a far better wat of heating you home.
    Put i guess it also depends what they are charging you for gas and electric.

  4. #4
    Join Date
    Feb 2007
    Location
    Las Vegas,NV
    Posts
    746
    At 40 degrees, a heat pump will blow plenty of warm air but, you have just barely scratched the surface. You need to have a load calc done on your home, and you need to make sure your duct work is adequetly sized for this size of system, and properly insulated. You also need to make sure your home is properly insulated also. A heat pump that might work fine at 40 degrees or less in one home may not do squat for a drafty old barn. If you go out and find a reputable company, they will be able to come in and answer all of your questions, perform a manual j, and more so decide what size system you need for your home. It kind of sounds like you are looking to buy and install this system yourself? where did you come up with the tonnage you need? Better look into this alot further first or you may end up with a system that doesnt suit your needs.

  5. #5
    Join Date
    Nov 2007
    Posts
    13
    So at 40degrees ourside, the HP can maintain 70 degree inside temp and that at warmer outside temps it can get the inside temp to warmer temps? That's the part I don't know about. I heard that at about 32ish outside, its a good switch-over temp to backup heat.

    In KS, propane is over $2/gal & going higher, while reduced electric rates for HP users for the 8 fall/winter/spring months is $.0467/kwh. So using the DOE spreadsheet link provided on another thread, it comes out that propane is about $40 vs about $5 for HP use and $12 elec heat for a mil BTU's I believe it was. So I am expecting my new 3ton 16 SEER 8.7 hspf 2-stage HP w/elect backup to save me a bunch! Us propane users are hurting!

  6. #6
    Join Date
    Feb 2007
    Location
    Las Vegas,NV
    Posts
    746
    No not entirely true, at 40 degrees, a heat pump may not keep your house at 70 degrees if it is poorly insulated! Like I said before, there is much much more that you need to have investigated by a pro. No one can answer questions properly unless they have alot more to go on.

  7. #7
    Join Date
    Nov 2007
    Posts
    13
    Sammy, oh no way am I trying this myself! I had numerous HVAC'rs come in to bid on removing my 20 yr old propane furnace that is breaking, to an all elec HP/elec backup combo, so we finalized on Lennox system w/20KW heat strip and 3 zone & wrapping the unfinished bsmt ducts. Right now I'm focusing on getting the increased elec circuit in by electrician & wiring run.

    I just wanted to understand more about the outside vs inside temp relationship which I know will differ between size/insulation of house, but I wanted to learn the general relationship in a somewhat normal situation (ie - are we talking HP's giving a 10 degree increase or 30 or 50?). If you are curious, I have 2200sf, 1.5 story, double paned low-E windows and good insulation in 20 yr old house. When there is little wind, the heater rarely kicks on all day/night. Thanks!

  8. #8
    Join Date
    Oct 2007
    Location
    Richmond, VA
    Posts
    103
    I'll give you an example of how I am using my HP. 70s during day, 61 at night outside temp is above 36 degrees at night and in the upper 40s to mid 50s right now. In the early morning it takes less then an hour for my HP to raise it to 70. I have gas as backup and is locked out above 36 degrees outside temp.

    When you do all electric from what I have read it is not worth it to do temperature swings like I am doing if your in really cold weather. I can't sleep well though with the temp above 65.

  9. #9
    Join Date
    Feb 2007
    Location
    Las Vegas,NV
    Posts
    746
    I have never taken temps of the air coming out of my registers, but I know that even on some 30 degree mornings, my unit still put out plenty of warm air. You will have to experiment with it to see just how comfortable you are when the temps drop, and how well it heats your house without running constantly. The best efficiency will be from the pump itself, the heatstrips will cost considerably more to operate. If the system is sized properly, and your ductwork sized properly and house well insulated, I think you will be very happy with the results you will get from your new system.

  10. #10
    Join Date
    Nov 2007
    Posts
    13
    So in general then, a HP can give you about a 25 degree bump from what is outside. I did learn about the lockout thing by reading postings on this great website. Wasn't thinking about warm-up time, so I appreciate you mentioning that as well. Thanks for the general info, HP's are new to me and I have equal people who love them and the low $$ they result in, and others (LOL mostly us females) who think they blow too cold or others who complain they are nothing but mechanical nightmares.

    BTW, I keep inside temp around 68-69 during day if I'm home and night/work hours about 65. And someone in a posting just said that HP's don't increase temps quickly so not to do a big setback, so I'll keep that in mind as well.

    The installer is nice and friendly so I already warned him I'm a closet techie so will be watching and learning as he goes about the install. its fascinating.

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,110
    With electric aux heat. You run the HP and aux heat at the same time. You don't shut the HP off.
    Contractor locator map

    How-to-apply-for-Professional

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

  12. #12
    Join Date
    Jul 2002
    Location
    37760
    Posts
    413
    btu=[cfm]*[1.08]*[td]
    3 ton roughly 1200 cfm
    3 ton roughly @ 17* low capacity +- 20,000
    3 ton roughly @ 47* high capaciy +- 35,000

    20000=[1200]*[1.08]* [temperature of supply air- temperature of return air]
    20000=1200*1.08*15.43 /// [80.43-65] or [85.43-70]

  13. #13
    Join Date
    Jun 2007
    Location
    Metro St. Louis
    Posts
    181
    Quote Originally Posted by stockgal2 View Post
    BTW, I keep inside temp around 68-69 during day if I'm home and night/work hours about 65. And someone in a posting just said that HP's don't increase temps quickly so not to do a big setback, so I'll keep that in mind as well.
    Here's where you *might* end up running up your electric bill...

    First of all, get a good thermostat (like the Honeywell IAQ). You need a way to keep aux heat off unless it's below a certain outdoor temp. This is my first winter with a new HP, and I've got mine set at 15*. If it's 16* outside, the strips won't come on. I'll probably have to pull that up to 20 or so.

    Basically, you want to keep your setbacks configured so that the aux heat does not come on. It's easier to recover from a daytime setback, as these are the warmest part of the day. However, nighttime setbacks will probably cause the strips to come on.

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