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  1. #1

    Geothermal Sizing - Under or Over Which is Worse?

    I am getting quotes for a geothermal retrofit in Lancaster PA (just West of Philadelphia) and am considering various options. One contractor gave me a choice of either a 2 ton or 3 ton (2-stage), saying that the 3 ton would provide essentially all my heating, the 2 ton would need some auxiliary. Another contractor only suggested a 3-ton system. I'd like to beef up my passive heating and insulation, perhaps even add a fireplace insert for really cold days, and get the 2 ton. In this way I'd be very efficient in the summer and reduce some load overall. But I'm a little worried I'll be burning a ton of firewood or using a lot of auxiliary - offsetting the whole point of going geothermal.

    I currently have an airsource heat pump that seems to be good for only about 30% of the really cold winter months (Dec - Feb), propane kicks in otherwise. I will get rid of the propane backup with the new setup.

    My question is this: how much better will the 2 ton geothermal be compared to a 10 year old air source heat pump? If I do much better with it, will the 3 ton be overkill? Is it better to be a little light on heating load ... or the converse for colder climates?

    Thanks for any thoughts.

  2. #2
    Join Date
    Jan 2004
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    PA
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    I'd ask them to do a load calc. Find out if its going to be too big for cooling. Last thing you wat is cheap heating, and high mold in the summer because of an oversized system.

    Did you get an estimate from Ressler and Mateer. Mike or Jim can do a load calc for you.
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  3. #3
    Join Date
    Oct 2007
    Location
    Eynon, PA
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    37
    You definatly need a cooling load calc to get the right size unit. I can tell you this: The Geo Unit will be much more efficient than the air source HP. The air temp is always changing, and when it drops too low your effiency goes down. With the Geo. the ground (or pond) always stays the same temp year round so the efficency is much much higher. Do consider getting a Water Furnace Envision Series if it's in your budget. Best unit out there! You can opt for the aux elec. strip heat (or keep the LP furnace), but if the unit is sized properly you won't need the backup too much, except in the coldest of conditions.

  4. #4
    Join Date
    Nov 2007
    Posts
    86
    If you choose the 3-ton 2-stage compressor with variable speed ECM blower you will not be oversized for heating or cooling. Your contractor should run the calcs though. The 3-ton choice should provide 100% of the heating load requirement for your climate (depending on the calcs!). Electric backup heat strips are still in order though. The 3-ton choice will also provide some extra capacity when needed, should you choose to install a desuperheater – particularly on very cold days. It may also be the better choice should you later decide to add a small addition to your home.

    Of course it will be more expensive but perhaps worth the cost. Run the numbers; do the calcs!

    Follow the advice of the installer you trust the most.

    SR

  5. #5
    Join Date
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    Quote Originally Posted by fsq4cw View Post
    If you choose the 3-ton 2-stage compressor with variable speed ECM blower you will not be oversized for heating or cooling.

    SR
    Wow, you can tell that without even seeing his house.
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  6. #6
    Join Date
    Nov 2007
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    86
    Quote Originally Posted by beenthere View Post
    Wow, you can tell that without even seeing his house.
    Re: beenthere:

    READ THE ORIGINAL POST!

    “I am getting quotes for a geothermal retrofit in Lancaster PA (just West of Philadelphia) and am considering various options. One contractor gave me a choice of either a 2 ton or 3 ton (2-stage), saying that the 3 ton would provide essentially all my heating, the 2 ton would need some auxiliary. Another contractor only suggested a 3-ton system.”

    Based on the fact that that he’s already received quotes from 2 contractors , I’ve offered an opinion to further qualify their findings – not mine. If you read my post more carefully, you will also note that I twice mentioned calculations (heat gain/loss), once strongly suggesting ‘Run the numbers; do the calcs!’.

    My last piece of advice was to ‘Follow the advice of the installer you trust the most.’ irrespective of what you, I, or anyone else NOT on site says or thinks.

    I stand by my original post; it’s sound advice.

    IMO

    SR

  7. #7

    2? No 3.

    Since the 3-ton is a two speed, I wasn't really too worried about mold/clamminess for the summer. Really, what I was wondering about was that if I go with the 2 ton, which is a better fit for cooling load and cheaper, if my added winter load could be offset by some passive heating, more insulation, a fireplace, and warm blankets (and as a last resort the 10Kw backup), without the cost of that backup negating the move to geothermal anyway. Not that we want to suffer, but we typically leave our home at 65 or 66 during the day 63 or 62 at night during the winter, which is lower than the temperature used by one of our contractor's load calculation (the other didn't share his calculation - if he did one).

    I think I will get one more load calculation and see what we can determine. I might even like to do a blower door test.

    Thanks - Dan

  8. #8
    Join Date
    Jan 2004
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    PA
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    Just because a unit is 2 stage, doesn't mean that it will have enough latent capacity to keep the humidity low enough.
    Any insulation or envolope improvements you can do will help in both heating and cooling seasons.

    A 2 stage in first stage capacity will be from 60 to 80% of full capacity. Meaning a 2 stage 3 ton in first stage could be at 2.4 tons capacity. With a latent capacity that isn't enough to keep the RH below 55%.

    Get a company to do an acturate load calc.
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  9. #9
    danpat,
    There are air source heat pumps now that can handle low
    temperatures without a backup.
    We install the Acadia heat pump in NJ and so far so good.

  10. #10
    Join Date
    Jan 2008
    Location
    Wisconsin
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    1,125
    Quote Originally Posted by fsq4cw View Post
    Re: beenthere:

    READ THE ORIGINAL POST!

    “I am getting quotes for a geothermal retrofit in Lancaster PA (just West of Philadelphia) and am considering various options. One contractor gave me a choice of either a 2 ton or 3 ton (2-stage), saying that the 3 ton would provide essentially all my heating, the 2 ton would need some auxiliary. Another contractor only suggested a 3-ton system.”

    Based on the fact that that he’s already received quotes from 2 contractors , I’ve offered an opinion to further qualify their findings – not mine. If you read my post more carefully, you will also note that I twice mentioned calculations (heat gain/loss), once strongly suggesting ‘Run the numbers; do the calcs!’.

    My last piece of advice was to ‘Follow the advice of the installer you trust the most.’ irrespective of what you, I, or anyone else NOT on site says or thinks.

    I stand by my original post; it’s sound advice.

    IMO

    SR
    Sound advice, but some people on here think their word is and should be the final word, cause, well, they think they're right and everyone else is wrong.

  11. #11
    Join Date
    Jan 2002
    Location
    East Grand Forks, MN
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    1,375
    Well Dan, for all we know you might need a 3.5 Ton unit.
    When i see your heat-loss and sens & latent heat gain, i can actually give you specific size based on your heat calc and equipment specs.

    Air Source HP are not bad, but either way,go with resistive heat as a backup or supplement.

  12. #12
    Join Date
    Jun 2008
    Location
    Lancaster Pennsylvania
    Posts
    60
    You ever find someone to install your Geothermal for you?

  13. #13
    We decided to focus on improving our insulation, ducts leaks, etc for this year. And, the three quotes were got were very high. Next year we plan to ask the contractor a neighbor used recently to put a geothermal unit to do ours. Our neighbor thought they would have a more reasonable quote.

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