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Community and Q&A

Air-source inverter heat pump vs GSHP (Geothermal)

gtmsmith | Posted in General Questions on

Hello and thank you for this awesome forum!

My wife and I are looking to upgrade our HVAC system. We have the original 31 year old single zone 4 ton system, outdoor ac unit and indoor oil fired forced air unit. Although they work, they are on their way out and wildly inefficient. If we kept oil, which is out of the question, we would need a new oil tank and chimney liner too.

I have narrowed down our options to two quotes/products and I am looking to garner some advice during this process but also help others when reading/searching for this type of decision in the future.

Geo Option (GSHP)
Climatermaster Tranquility 30 4 Ton
Complete removal of old equip.
Merv 11
Aprilaire 700 humidifier
Air scrubber Plus
Two 320′ wells/permits etc. 
$29K Total before tax credit
$21.5k after tax credit

Air Source Heat Pump Option
Daikin Fit 4 Ton
Inverter Style Heat Pump
Complete removal of old equip.
Merv 11
Aprilaire 700 humidifier
Air scrubber Plus

-climate zone: I am on the 4a/5a line (S.E. PA 19382)
-31 year old contemporary home
-2700 sq/ft two story living space (basement and attic are not conditioned)
-well insulated for 31 year building
-all doors are now new
-all windows are original and poor (I will slowly be replacing all of the casement windows) 
-I am continually adding insulation in areas. The basement is well insulated and the attic is insulated but I will be air sealing things soon and adding more blown in insulation

We are easy going and happy with 66-68F in the winter and 74-76F in the summer on the T-stat. We have been happy with single stage heat pump heat in previous winters in a much tighter and smaller home prior to this. 

I plan to add a small wood stove for some supplemental heat as well soon but it wont heat the entire house.

What are your thoughts? I am leaning towards the Inverter Style Air Source Heat Pump because:
-its cheaper (about 3.5k difference)
-the efficiency gap, to me, and from what I have read, doesnt seem big enough
-its got a longer warranty 12 compared to 10
-its got 18mos no payment no interest which can help me get some more work done on this major renovation in the coming year (no options avail for geo and well)
-it wont tear up the yard 
-it doesnt have the ‘what if when drilling’ factor im a bit afraid of because of the super high water table and amount of stone in my area

Did I just make up my mind? Help!

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  1. joshdurston | | #1

    Your last two points seal the deal for the ASHP.

    Some pros towards the ASHP is the modulation (fan and compressor), and relative simplicity of the system. The GSHP is on off with maybe an unloaded first stage on some models, the ASHP will run longer and modulate to the load for better comfort. I think inverters pair up with solar better too since they don't have the inrush. If you want to consider solar with islanding in the future, the ASHP will work better on a smaller inverter due to the lack of inrush current.

    GSHP works as a technology (my parents have had one for almost 25 years with essentially no issues or maintenance costs, and low utility bills to go with it). But the ASHP are so good these days it's hard to justify invasiveness of drilling and the higher capital cost. Farms with the land for big simple horizontal loops are the best applications IMHO.

    PS: I wouldn't install a humidifier (or the air scrubber). Just install an over-sized MERV 13 or better filter. Too much risk for the humidifier. Put the money towards air sealing which will raise your RH in the winter to the point of needing to vent to lower it. High merv filter and balanced ventilation with recovery is the way to go for air quality.

  2. gtmsmith | | #2

    Thank you^

    The nature of the heat pump will be more humid than my oil heat anyway so I think you have a good point here.

    The Tranquility 30 geo option is a two stage unit. While not variable, it at least runs at about 65% and 100% loads. (The variable gshp are too expensive for me)

    I am not opposed to solar at all, and have a very good set up to take advantage of it someday, but cant afford it at the moment (And no i will not 'rent' solar haha)

    1. joshdurston | | #3

      I will say I'm not familiar with the Daikin Fit.
      It seems to have a relatively low HSPF of UP TO 10. I kinda see 10 as the minimum acceptable HSPF in 2020 ideally 12 or higher in heating dominated areas. You might want to check out the Carrier Greenspeed central ASHPs as well. Mitsubishi has air handler style cold climate ASHPs as well but I suspect they might be more expensive.

      That is a good heat pump if you go GSHP route (but I still recommend the ASHP in your case). I might actually choose the the GSHP over the Daikin fit, but would choose a higher performing ASHP over the GSHP.

      I used to work for the ClimateMaster distributor in Canada and can vouch for the Tranquility, I know a bunch of people that have had the TTV27 installed for years. You have to be confident with your contractor with geo, since there are a lot of variables to get right (or wrong). With ASHPs sizing is often the biggest hurdle, and you can do some legwork yourself there.

      I suspect the 4 ton may be oversized slightly, with a GSHP you want enough capacity to cover a high percentage of your annual heating BTUs, but this may mean sizing for only 70-90% of your calculated peak load. You would make up the difference with electric heat (which I would keep turned off until you need it). This balances your up front and operational costs.

      ClimateMaster has some decent software called GeoDesigner which uses your heat loss info and balance point, utility cost and climate bin data to calculate ideal sizing. But you need a heat loss to make it work. Maybe you can do a reverse calculation from your old system
      You might be able to download it yourself from here:
      But I'm not sure if you'll be able to activate it as a non dealer.
      The pressure drop calculator is also a good tool. A lot of systems aren't pumped right wasting a bunch of performance.

      Anecdotally my Parents have a similar age 1995 2700sqft. house 2x6 construction with fiberglass batts here in Southern Ontario. They have heated it with a 3ton heat pump and have had the breaker off to the electric backup heat the entire time. House doesn't drop below 70f on the coldest nights but the heat pump runs at basically 100% duty cycle. They have a generously sized horizontal ground loop (I think a 2x 400 yard 1.25 in parallel).

  3. Trevor_Lambert | | #4

    Have you done a heat loss/gain calculation? 4 ton sounds way too big for the climate you're in and the house you've described. I'd expect a 4 ton unit could heat an uninsulated house with single pane windows in climate zone 4. Geothermal already loses in your current comparison, and if you end up needing a smaller system then it just tilts even further away from geothermal making any sense.

    1. joshdurston | | #5

      Ordinarily I'd agree with you, but with just a $3000 gap between the two (which might shrink to $0 with right sizing), I don't think you can outright dismiss the GSHP. Done right the the GSHP could easily beat the ASHP operational costs, and with a similar install cost it might be worth considering. Shrinking the system is going to reduce the GSHPs costs a lot more than the ASHP.

      Like I said before overall I think ASHP are the way to go, but if you can keep the GSHP costs under control I think it's worth considering in this case.

      One more thing. Are you going open loop in the wells or using them as bore holes with tubing inside them? Open loop GSHPs are a huge pain with mineral buildup and associated maintenance costs to descale the HX. I'd only consider a closed loop for long term stability. I know of a couple people near me that paid substantial money after the fact to convert to closed loops after initially doing an open loop install.

      Also, I am surprised the the GSHP (minus the wells) was cheaper than the ASHP. Is this thru the same contractor?

      1. gtmsmith | | #8

        That well design is closed looped, and I agree - this is the best way to go. The well drilling price is separately contracted and these guys are the best and most recommended in the area (they were about 1k more than the other 2 quotes I got - and all of them quoted the same vertical 320' well closed loop etc)
        So if I go GSHP, the well is set and locked at about - 11.7k

        Below are my different contractor quotes... all of these are reputable companies. I live in a pretty competitive area with a lot of local contractor options.

        Contractor 'A' gave me two options
        -daikin fit ashp as listed above in the original post - 18k
        -same CM Tranquility 30 gshp option as above but was - 24k
        (then add 11.7 for wells)

        Contractor B is a small mainly geo contractor that only quoted me what i listed in the original post. He stated he doesnt have much experience with inverter heap pumps and sticks to geo mostly. This price is almost alarmingly low but he's small and known to have more fair pricing - 17.2k
        (then add 11.7 for wells)

        Contractor C
        Trane XV20i ASHP - 21k
        Water Furnace 5 Series GSHP - 24.2k
        (then add 11.7 for wells)

        Contractor D
        daikin fit ashp - 18k
        But these guys will not get my business and i wont bash them here

        1. joshdurston | | #9

          Some areas have a contractor who is less expensive but as good or better than the competition. I knew of one just North me. When I was with GSHP distributor other contractors would constantly complain about their low pricing, but they did high quality installs for cheaper than just about anybody else.
          Was a small well run Dutch family business which did GSHPs exclusively.

  4. gtmsmith | | #6

    Thank you guys - really learning/researching a lot and loving this process haha. This is just too much money and too important to throw up my hands and pay the first person that quotes us and solely trust them.

    A manual J was performed and we hit the 4ton size right on. Being a contemporary we have a lot of large (leaky) windows... the only thing that was noted when this was completed was that I am down a return or two and that my returns weren't sealed well (sealing them and increasing that performance is easy and both options/contractors told me they will show me how/what to do while they are here so I can save and do that myself)

    The Daikin fit system that I was quoted comes out to 8.8hspf on my quote it says... and 'up to 10hspf'

    The Carrier Greenspeed does look like a nice option and says 'up to 13hspf' so what is it really?

    I would assume though that the Carrier is going to cost more, and get close to my all in GSHP option (Which by the way that GSHP option I have is nearly 5-10k less than the other two quotes I had and one of them being the same exact CM unit)

    For my ASHP option, we were going with 20kw of back up heat and were only going to run 10kw first to see if that is enough but outfit the unit with 20kw.

    With the most recent winter we had I would have maybe used back up heat 5 times max (it was a very mild winter here)

    1. joshdurston | | #7

      To me the guys that were $5k to $10k higher were probably the norm for GSHP pricing (and solidifies the case for the ASHP). Were the others using open wells or closed loop bore holes? Someone who underbids the job is unlikely to have the resources to make things right if things go sideways at all.

      From my point of view getting rid of the humidifier and airscrubber might equalize the cost to step up to a higher efficiency ASHP. The carrier might be 10%-30% more efficient. It's hard to use the HSPF to actually predict precise operation costs because it depends on the load profile and local climate. But you can use them as a point of comparison.

      Looks like the Carrier HSPF would be 10-11 so not a huge difference.

      Here is a good resource for comparing equipment:!/product_list/

  5. MattJF | | #10

    Have an engineering firm do a load calc before doing anything. I bet your loads are not 4 tons, but contemporary homes can have a lot of glass, so we would need more info.

    Contemporary homes can also have a lot of issues with variation in solar gain between different sections. Is this a current issue? If it is, two separate Fujitsu slim ducts may be a good option, but we need a heat load calc to figure that out.

    Sizing is really important with the systems to hit good efficiency.

  6. gtmsmith | | #11

    OK - I will look further into a local firm to aid in some of this.

    The manual J resulted in about 46800 if I remember correctly (this was contractor D - I dont have the calculation paperwork but he did go around and measure sq/ft/windows/etc. etc. and came back the week later with the info/quote)

    We have a ton of windows.
    10 double casements that are 5'x5'.
    6 single casements that are 2.5'x5'
    2 small casements

    1. Trevor_Lambert | | #12

      You can rarely trust the contractor to do a manual J, especially if they don't show you how they arrived at the number. He took some measurements, but he still could have just used a rule of thumb, or just entered inaccurate info into the program. There's an article on here somewhere about who should perform your manual J. You can also use your heating bills, but you'd have to account for any improvements you'd did or plan to do soon.

  7. walta100 | | #13

    Without seeing the mini split bid and an aggressive manual J not done by a bidding HVAC contractor it is just a guess and mine is without tax credits GSHP rarely pay off. With credits and low electric rates GSHP do not pay off. With credits and high rates in zone 1-4 in a PGH GSHP do not pay off. With credits and high rates in zone 4+ in a leaky uninsulated house GSHP do pay off.

    We often see mini split bid s that are 300% over sized with a head every place that would have put a register.

    A manual J is worth what you pay for it. So any one “free” one is worthless.

    The best way to look to compare the cost of ownership of the 2 systems would be to computer model the home with the 2 options in BEopt. Entering the bid pricing and SEER rating into BEopt with your interest rate and electric rates will give you a real answer.


    1. gtmsmith | | #15

      just to be clear... no ductless mini splits here... just one whole house ducted inverter ASHP (Daikin Fit)

    2. Expert Member
      NICK KEENAN | | #18

      >We often see mini split bid s that are 300% over sized with a head every place that would have put a register.

      Hijacking the thread here, but I'm curious, what is the best practice for head placement when you have multiple rooms? If you've got three bedrooms and two baths on the same floor, how to you serve them with mini-splits? Ducted?

  8. gtmsmith | | #14

    And that makes sense
    I wonder what that would cost around me
    Everything around here is a little inflated
    Looking into it now
    Because I would agree perhaps a 3.5 ton unit tips the scales on some of these quotes and makes this clearer for me

  9. cliffmarck | | #16

    I went through a similar decision this past Winter.

    I ended up with a Daikin Fit 4 Ton Heat Pump. I'm told I was the first install in all of Canada for the heat pump - I had to wait 5 weeks for it to come in. It's amazing and it's my belief that they are sandbagging their numbers. It was able to heat my house down to -20 C without turning on the auxiliary heat - and continues to use way less energy than my original calculations. My only issue is not with the unit - but with my installer for doing a duct design saying one thing - then me coming home from work to see an install with smaller ductwork and more transitions than necessary causing an unreasonable increase in velocity. But I digress.

    I didn't have the same rebates as you do - so my decision between GSHP and ASHP was easy. I spent quite a bit of time comparing relevant HSPF's between the Daikin Fit, Mitsubishi Zuba (Canada version of the P-series I believe?) and the Carrier Greenspeed.

    Costs for the Daikin was a few thousand less than the Mitsubishi and quite a bit less than the Carrier. Although the Carrier did better from an operational costs standpoint - it was priced at a point where it couldn't make up the difference over the life of the unit. It also had quite a few reviews indicating it might be over-engineered and loud at lower temperatures.

    I would echo what everyone else says about ensuring you have a proper heat calculation done - as well as ensuring your ductwork is sized to handle the airflow. I don't believe this should be a problem considering you currently have a 4 ton unit running and haven't mentioned any noise/turbulence issues.

    I pay 0.15 cents a kw/hr on average and paid an additional $100 during a cold month (average around -5 to -10c) and $50 and $30 the past couple months as it was still somewhat cold but moving into the shoulder season definitely.

    I think most manufactured HSPF'S are done for your Zone so you won't have to do much extra work trying to figure out relevant costs.

  10. cliffmarck | | #17

    P.S. I went with an air handler and Daikin One Stat. Let me know if you have any specific questions about any of the units - as I couldn't find any reviews of it online at my time of purchase and still can't find much information on the Fit HP system. The outdoor unit is small and runs relatively quiet compared to the conventional units. I would recommend it 100% and am an annoyingly picky type of person.

  11. gtmsmith | | #19

    Cliff, thank you for the reply! That is awesome... it sounds like we are kinda similar haha... I am really glad you posted and have the same system I am leaning towards.

    I cant find any real customer reviews on the Daikin Fit system either and part of that makes me worry but the other thing with that is; people more often get on the internet to review products they are unhappy with than happy...

    I know you dont size a unit by sq/ft but about how big is your home with that 4ton and are you full of windows?

    My current ductwork by all contractors that have been out has been deemed well designed/sized, just short a return or two.

  12. cliffmarck | | #20

    I would try to get a couple of more quotes. I know pricing varies regionally and I got a discount on the unit because it was brand new at the time - but I paid about $12k for the heat pump, air handler and stat combo. That's Canadian with a 12 year parts and labour warranty.

    Heat pumps do double duty. I sized mine for the heat load because that is what requires the most juice in my neck of the woods. I actually sized it to only carry the full load down to -4c - using electric auxiliary strips to take over - but it has managed the entire heat load on it's own down to around -20c. We keep our heat around 21 c (I feel shame posting this on a green forum).

    We are in a log house which is a bit leaky in spots for now and we have quite a few windows. It is a story and a half - about 2500 square feet above grade with another 1150 conditioned basement. Quite a few windows.

    Returns are pretty easy to add - you might have some minor framing and drywall work ahead of you at the very worst.

  13. cliffmarck | | #21

    One thing that I definitely appreciate about an ASHP over a GSHP - is that the installers can't mess too much up. There are a LOT of people around here who have horror stories over undersized GSHP's that use only auxiliary which turns out costing them a fortune. It's a shame because it gives great tech a bad name. When it's done right - it's amazing.

  14. Expert Member
    Dana Dorsett | | #22

    >"...single zone 4 ton system, outdoor ac unit and indoor oil fired forced air unit.."

    Since you have a history on this place, you can derive the design heating load from the wintertime oil use using this method:

    You can also estimate the cooling load by measuring the system's duty cycle on afternoons that are running near the 1% outside design temp:

    Don't count on modulation to save you from the comfort & efficiency deficiencies of oversized equipment in either heating or cooling mode. For large air handler ducted systems with limited modulation range ( or single speed geo system) it can be more comfortable to even UNDERSIZE it- have the heat pump cover the load at the 95th or 93rd percentile temperature bin, and use strip heat to cover the difference. Oversizing by more than 1.2x can sometimes be a comfort & efficiency issue for systems with only a 2:1 or smaller turn down. Oversizing by 1.5x is usually fine if the turn down ratio is 5: 1 or higher.

    In my area ground source heat pump systems are usually more expensive than a right-sized modulating air source heat pump plus enough rooftop PV to cover more than half the heating/cooling energy use (sometimes enough to cover all of it.) Clearly YMMV.

  15. gtmsmith | | #23

    Had my third Daikin Fit ASHP today... Ill have the formal quote in a day or two.

    4k less than what I was about to go with... thing is, these guys swear up and down that aero sealing my system would be a good idea (an additional 2.5k and this was the first I have ever had this proposed to me) I was just going to seal up and insulate things well in the basement and I think I am fine with just that.

    He also believed a 4ton unit was best due to the previous unit size, the size of home, and amount of large windows, and positioning of the house. He told me the modulation would indeed help if actually oversized too - which kinda makes sense to me but Dana Dorsett you said otherwise above, could you elaborate a little?

  16. joshdurston | | #24

    Is the Daikin Fit a true cold climate ASHP.
    It seems like it will continue to heat when it's fairly cold at a reasonable efficiency, but the capacity drops off pretty severely from what I can tell.

    It heats to -20F, but you really need to look at the capacity at colder temps to see if it's appropriate for you.

  17. gtmsmith | | #25

    The 'Energy Star Guide' I just referenced (which states its reference is manual J) claims for my area:
    89F for 1% Cooling temp
    13F for 99% heating temp
    1.7 HDD/CDD Ratio

    1. joshdurston | | #26

      Ok, you have close to 35MBtu/hr at your design temperature (13F) which might be fine.

      I must have misread the ASHRAE table I looked at.

  18. Jon_R | | #27

    Note that there is a lot more to GSHP borehole performance than just the depth (eg, thermal grout). Investigate further is anyone plans to use less than 200' per ton (of design day load, not HP capacity).

  19. Expert Member
    Dana Dorsett | | #28

    >"He told me the modulation would indeed help if actually oversized too - which kinda makes sense to me but Dana Dorsett you said otherwise above, could you elaborate a little?"

    Turn down ratios are not infinite. If you oversize by very much the lower efficiency of cycling on/off during the shoulder seasons can eat up more than the amount of "extra" heat -strip power use of a slightly undersized system. The oversized system will cycle more, modulate less which provides lower comfort too.

    I couldn't find the minimum output specs for the 4-ton compressor with the 4 ton air handler, but per the NEEP data the 3.5 ton air handler with the 4 ton compressor has a respectable (for this type of system 4.2/1 turn down ratio, dropping as low as 9500 BTU/hr @ 47F:!/product/30795

    But that's still substantially higher minimum than the 6700 BTU/hr minimum of the 3 ton system, which has a 5.1:1 turn down @ 47F:!/product/30772

    FWIW: I live in a sub-code 2x4 framed 2700' + (1600' of insulated basement) antique (1923) 1.5 story house with clear-glass windows. My heat load at +13F would be about 32,500 BTU/hr, which would make the 4 tonner a better fit for me. (Though I'd probably opt for a Fujitsu 36RLXS with the vapor injection compress instead, for better efficiency and capacity at +5F, my actual design temp:!/product/25352 ) That's probably a thermally crummier house than yours, if comparable in size.

    The 3 ton Daikin would probably be a better fit than the 4 tonner for tight 2700 foot 2x6/R19 type house with low-E windows or maybe a 2 ton or 2.5 ton Fujitsu RLGX:!/product/25350!/product/25351

    Note the minimum modulation of the 2 ton Fujitsu is 5400 BTU/hr @ +47F, substantially better modulation range than the 3 ton Daikin, and comparable capacity at +5F to the 4 ton Daikin.

    The minimum modulation of Fujitsu's 2.5 tonner @ +47F is comparable the the 4 ton Daikin but substantially more l0w-temp capacity.

    Rather than guessing what your heat load is, use the oil burner to MEASURE it:

    As crude a method as that is, it's way better than a WAG.

    Use the duty cycle on the existing 4 ton AC to estimate the cooling load. My 1% cooling load (in a crummier house than yours) is under 2 tons- it used to be under 1 ton before I got rid of most of the PM shade taking out three large trees (which had become a hurricane threat to the house.) I'd be shocked if your cooling load were more than 3 tons, but it might be over 2 if you have a lot of unshaded west facing window.

  20. gtmsmith | | #29

    Unfortunately I really cannot accurately calculate my heating load, I do not have enough concrete data to use the method you've shared a few times now. Not only did we have our most mild winter on record here this past season, we didn't move in till the first of this year. I had mis-readings on oil fills because of the poor tank and float - its a mess and this is why I am getting rid of it among many other reasons. Additionally, from July-Dec when I was renovating for us to at least be able to live in it we kept the house at 80 in the summer and 60 in winter until we moved in. My 31 year old Williamson furnace and burner paperwork is here but says 56000 to 420000 btu/hr input and no output details on it or in the old documents

    just a note too: I am 2x4 construction and when i say my windows are bad... they are bad haha. when the wind blows, the curtains wave too lol (I will be replacing the worst ones soon on the obliterated south west side that is completely exposed and destroyed from the sun)

  21. Expert Member
    Dana Dorsett | | #30

    >"just a note too: I am 2x4 construction and when i say my windows are bad... they are bad haha. when the wind blows, the curtains wave too lol (I will be replacing the worst ones soon on the obliterated south west side that is completely exposed and destroyed from the sun)"

    When a house is that air-leaky cutting a ton of heating or cooling load can be pretty cheap by addressing the deficiencies of the building envelope, and will buy a lot more comfort than up-sizing the equipment capacity by a ton.

    Running a Manual-J on the "after building upgrades" version of the house and going with the smallest equipment reasonable for that load may cost you a bit in extra strip heat use in the near-term, before upgrades if it's going to take you a year or three to finish it, but that cost adder is offset by the lower equipment cost.

    It's almost always the case with HVAC equipment that replacing like-for-like capacity-wise is a mistake, even when NOT planning to upgrade the building envelope. A 4 ton air conditioner for a 2700' house is almost always sub-optimally oversized, even for the "before upgrades" version of the house.

    If you haven't already, taking a peek at Nate Adams' short videos & free book chapter downloads is worth it when pondering the overall picture on a house undergoing upgrades. The notion that modulating equipment is going to just make all those issues go away isn't well founded.:

  22. gtmsmith | | #31

    awesome thank you^ I have come across this site before in research but haven't done much else with it yet - I will now!

    Just had a call with my most recent and cheapest Daikin Fit contractor/quoter (Ill call them Contractor E)... he shared the formal quote too. He told me after I pushed some that he came up with me needing a 3.3 ton in his 'special software calculator' but still recommends 4 ton for the possibility of me having all 4 bedrooms full of kids someday and that the inverters are just fine being slightly over sized. Also stated I would be saving much at all 3.5 ton compared to 4.

    The humidifier I have left out now because I can install an Aprilaire 700 myself... they are sometimes $200 on amazon and I am not going to spend $1k with these guys to have it supplied and installed for me.

    He offered the following upgrades:

    -Reme Air purifier installed at $1400 (This is interesting but seems pricey)
    -Aeroseal the ductwork at $2500 (This doesnt interest me)
    -aprilaire merv16 filtration system for $500 (This seems like something else I can easily do too but there is more here lol - what if i dont buy this? what filter will it come with? this is just a filter housing from what i am researching so this seems like a joke)

    something else i must sure up too is he's only quoting 10kw aux heat strip... the others quoted 20kw and said they could hook up 10, and then have the other 10 for a later date if it seems it would be needed. (cant they turn on in 5kw stages?)

    Their 'cash price' is 12.4k without those add ons above... this seems MUCH more in-line with what others have paid and what I expected.

    Perhaps Contractor A, whom I trust the most, will come down in price a bit?

  23. Expert Member
    Dana Dorsett | | #32

    >"He told me after I pushed some that he came up with me needing a 3.3 ton in his 'special software calculator' but still recommends 4 ton for the possibility of me having all 4 bedrooms full of kids someday and that the inverters are just fine being slightly over sized. Also stated I would be saving much at all 3.5 ton compared to 4."

    Bigger is NOT better, even if the upcharge is small. (Nate Adams has returned a 4 ton heat pump when a 3 tonner was specified.) Even if they were going to charge for a 3 ton, if they calculated a 3.3 ton load, go with the 3 ton, not the 4.

    A primary reason to go with the 3 ton rather than 4 is comfort, not up-front cost. The difference is how low it can modulate, which translates into longer more comfortable run times. The minimum output of the 3 ton in heating mode at +47F is 6700BTU/hr, compared to at least 9500 BTU/hr (it might be higher- that's what it is with the 4 ton compressor and 3.5 ton air handler), which is a substantial difference.

    Let's assume the heating load at +13F is about 30,000 BTU/hr (a shade lower than the output of the 3.5 ton Daikin w/ 4 ton compressor so about what a mythical 3.3 ton Daikin would deliver. At an indoor temp of +70F and outdoor temp of +13F is a 57F difference. So the load grows by about 30,000/57F= 526 BTU/hr per degree F below 70F. (It's actually more complicated than that, but this is a good first-approximation.) So at +47F the load is about (70F - 47F ) x 526 BTU/degree-hour = 12,100 BTU/hr only 2600 BTU/hr above the minimum output of the 4 tonner, but 5400 BTU/hr above the minimum output of the 3 tonner. Even on sunny winter days when it's in the 30s with the solar gain the 4 tonner would be cycling on/off rather than modulating, but the 3 tonner would be idling along pretty much continuously at low speed.

    Then when you factor in the pinky (if not a full thumb) on the scale of most HVAC contractor's load calculations it's actually a bit worse than the above estimate- the 4 tonner might be cycling on/off at your AVERAGE wintertime outdoor temperature, even on cloudy winter days, but the 3 ton almost certainly wouldn't. This is how the comfort benefits of modulation get defeated.

    An oversized high MERV pleated filter is a good thing- whether it's worth $500 depends. In my house there is an Aprilaire 2400 filter (16" x 28") that takes 6" deep pleated media, and run MERV 11-13 in it without trouble with a ~1500 cfm air handler. It keeps the ducts pretty clean, and is able to even clear burnt-toast smoke reasonably well (!). With a lower cfm system it would do even better.

    >"something else i must sure up too is he's only quoting 10kw aux heat strip... the others quoted 20kw and said they could hook up 10, and then have the other 10 for a later date if it seems it would be needed."

    A 10kw heat strip is adding 34,120 BTU/hr to the heat pump output, which is more than your entire heat load, and more than the 4 ton Daikin delivers at +13F. Even at -5F the 4 ton heat pump would still be delivering 16,000 BTU/hr (+34120= 50,000 BTU/hr, well over your actual load at -5F.) The 3 tonner is good for 14,700 BTU/hr @ -5F.

    A 20kw heat strip would only make sense if it could hit temps where the output of an R410A refrigerant heat pump becomes zero (about -40F), temps not seen in your neighborhood even during the last ice age. "Merely" 10kw strip heat is fine. The strip heat will cycle on/off when needed, and won't make the power drop to the house jump up and down when it switches on or off.

    >"The humidifier I have left out now because I can install an Aprilaire 700 myself..."

    And you SHOULD leave it out, probably forever!

    Humidifiers can destroy the house with sheathing rot if used improperly, and should not be necessary for maintaining human-healthy & comfortable in your climate. Air sealing the house to something close to current code max could even require wintertime DEhumdification to keep the indoor dew points low enough to be safe for the house. Shoot for 30-35% RH @ 70F and you'll be fine. Over 40%RH @ 70F indoors during the winter starts to become a problem for the house, even though the humans are still happy and healthy at 50%.

  24. gtmsmith | | #33

    Thank you VERY much for all of your responses and knowledge^

    I am set on ASHP and this Daikin system, no humidifier, no 'air purifier', UV light (if it doesnt void manufacturer warranty), quality MERV 13 horizontal filter housing.

    I will carefully relay some of this with my two contractor options too on sizing.

    Now I just need some advice from this forum on how to contact the contractor I 'want' and tell him someone is $4k less than him... and not get him mad haha

    1. MattJF | | #34

      From experience, just tell them what you want installed. Be confident in it and don't try to justify it. Trying to justify things is often not productive. Write up the specs/model numbers for what you want and ask for the each contractor to provide their best price.

  25. bliljequist | | #35

    I am going through the exact same process for a 1950 square foot house in Seattle. I have been using the calcunow Manual J tool to calculate load. It is a subscription based monthly pay as you go service so for a homeowner working on questions like this it is very reasonable cost wise. It is well worth doing - it took several hours to input the info, but then you can play with different scenarios of how you might improve the house to lower the heat or cooling load. You will see immediately how responsive it is to air sealing for example. I have been working towards a passiveish performance level, but need to do the HP now - so this is helping me realize I do need to finalize the crawl space retrofit now to bring leakage and duct loss down, because it is consequential enough to impact ASHP sizing significantly (from around 40k to 30k heat load).

  26. bliljequist | | #36

    I also want to mention that if you poke around long enough, you can find all the technical data for the various heat pumps out there. This data goes way beyond the broad HSPF numbers and shows you the coefficients of performance (COPs) at different outside temperatures (higher is better). You can actually see what units perform at in your climate. This is typically how commercial HVAC design is done, but just eyeballing the numbers is revealing. For example, at 47F, the Daikin Fit COP is 3.1 and the Carrier Greenspeed is 3.93 (both 42k units). That is a very typical outdoor temp in Seattle and certainly enough to pay attention to.

    Here are the links to these docs:

  27. gtmsmith | | #37

    Just some follow up here (Thank you EVERYONE for the comments and advice along the way)

    I am set on the Daikin Fit ASHP system with 10kw back up
    I spoke to the contractor we liked and trusted the most (they had the most experience with these units too) and requested him to re-visit his quote and get closer to our much cheaper quote. He got within $200 (Amazing how he was able to just chop off $3k - yeah)

    He told me that he had recent training direct from Daikin that insists these units get a surge protector so they are adding that.

    They are doing all brazing with Nitrogen of course too.

    He removed the 'temperature averaging sensor' from his quote as well but I dont really see that as something I really need with a unit typically just running low and slow for extended time.

  28. gtmsmith | | #38

    Circling back to this...

    We have had our Daikin Fit Inverter ASHP in for almost a month now... so far, so good. Its been 90 everyday and 75 at night since we had it installed and it barely cycles on and off and typically is just running quietly low and slow in the background. This has reduced the temp differential from upstairs to downstairs by 3-5 degrees F too and has controlled humidity well too. (I do still need to add more insulation in the attic and air seal)

    Also here was some good reading I found on oversized inverter/variable systems:

    I will share more on my system as the year progresses

    1. Jon_R | | #39

      A line from that paper that needs repeating:

      "Our research found that FC cooling systems can provide excellent indoor RH control, even when substantially oversized"

      Compare this to some VC inverter cooling systems that are known to often produce no RH control, even when perfectly sized to design load.

    2. joshdurston | | #40

      Did you end up with the 4ton unit?

  29. washxhouse | | #41

    This was hugely helpful to me as I'm in a 1987 contemporary house with loads of windows in 18977 (right down the road from gtmsmith, relatively speaking) and looking to replace my heat pumps as well.

    Gtmsmith - do you mind sharing the name of the contractor you ended up hiring? I've had two conversations so far, in both of which the contractors told me something along the lines of 'I don't go for that calculation stuff - you look at the square footage, you look at what was there, you size up a little to be safe, and there you go'. I really want to work with someone who sees the value in doing the math and have nowhere to start....

  30. gtmsmith | | #42

    Yes I would be happy to help or share more...

    I did get the 4 ton Daikin Fit ASHP unit. It is probably oversized like many have said. I got to a point where I needed to just get it done. I was told the same thing you were told "we size up to be safe" blah blah. I didn't end up with someone that 'sees the value in doing the math' - I didn't find a single contractor around here interested. This is ultimately what led me running out of time and extremely frustrated. I will say that I am very glad I went ASHP and specifically inverter style.

    I am not going to publicly bash/list the company names on here. I will however welcome a separate conversation on this with you. I can share my google voice number or my email if you'd like or if there is a safe way to do so on here!

    1. washxhouse | | #43

      Just saw this reply! I'm getting near decision time on my end but would still love to compare notes if you're willing - I don't think this forum has direct messaging but if you'd be willing to email please reach me at doctor handshake (no space) at ... would appreciate it!

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