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Community and Q&A

GSHP and an endless pool

user-5644012 | Posted in Mechanicals on

We have slowly been renovating our 115 year old, 2200 sq ft farm house over the past 12 years and live in northern Michigan (climate zone 6). This year we are replacing the 60 year old aluminum siding and roof and upgrading the walls to r30 and the roof to r60. We are also adding a 2425 gal endless pool/spa to the outdoor covered porch. I understand an outdoor pool in northern Michigan probably doesn’t fall into the category of green building but it will definitely be fun!

Five years ago our 50 year old fuel oil furnace was replaced with a 5 ton GSHP. Any thoughts on tying in the pool and spa to the GSHP? Our plumber recommended installing an additional 2 ton to heat the pool exclusively. From reading other discussions, the 5 ton GSHP is overkill to heat our home (especially with the upgrade in insulation) and I thought it might be able to heat both. If it is, any thoughts on how it would be done?

Thanks for the insight,


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  1. GBA Editor
    Martin Holladay | | #1

    This question can't be answered by guessing. It can only be answered by math.

    You need a good heat loss calculation to determine your home's heat load, and you need to ask the pool manufacturer to supply a BTU/h budget for pool heating. Once you have that information, you'll know whether your 5-ton ground-source heat pump has any extra capacity, and whether that extra capacity is sufficient for pool heating.

  2. user-5644012 | | #2

    Thanks for your reply. It seems that I can spend money on an additional heat pump or additional insulation. I'll talk to our contractor to see if he can perform the necessary calculations to see what we need.

  3. GBA Editor
    Martin Holladay | | #3

    I'm not sure why you have concluded that "it seems that I can spend money on an additional heat pump or additional insulation" if no one has yet done the math.

    It's possible that your heat pump system is big enough -- but you can't determine that unless you perform some calculations.

    In most cases -- unless your house is already insulated to a very high standard -- "additional insulation" never hurts, of course.

  4. STEPHEN SHEEHY | | #4

    Ryan- a lot will depend on whether the pool is indoors or out and in the ground or above the ground. A well insulated pool in ground indoors with an insulated cover will need much less energy to stay at temperature than if it sits on top of the ground, outside in a cold climate.

    Enclosing the porch, even without heating it, can make a big difference in energy use. It will also have the advantage of obviating the need to shovel snow when you want to use the pool. Some big doors or windows can give you the feeling of being outdoors without the bother.

  5. charlie_sullivan | | #5

    If your GSHP is a typical water-to-air heat pump, that distributes heat to the house through ducts, I don't see a straightforward way to use it to heat the water in a pool, even if it does have extra capacity. If it is a water-to-water heat pump, that provides heat to the house through a hydronic system (radiators, radiant floor heat, or fan-coil units supplied with heat through hot water pipes), then you could use any extra capacity to heat the pool.

    If it has been supplying adequate heat to your house, and you are upgrading the insulation, it will have spare capacity once you have finished improving the envelope. Whether the spare capacity would be enough would theoretically be determined by calculating the heat required for the pool, but without a way to deliver the heat to the pool, it's a bit of a moot point.

    I suppose you could get a water to air heat exchanger and use it as an air to water heat exchanger, running the air from the GSHP to it through a very short duct, with zoning added to the GSHP duct system so it could supply heat to this heat exchanger even when it wasn't heating the house. The hardware to do that wouldn't be very expensive, but you'd need to get a mechanical engineer to design that. Adding a 2-ton GSHP for the pool might end up costing about the same, and would almost surely be more efficient.

  6. STEPHEN SHEEHY | | #6

    You might also want to compare the cost of the additional GSHP to adding enough PV panels to heat the pool with electricity.

  7. user-5644012 | | #7

    Thanks for all of the help. This is an incredible website. I live in an area where green building isn't prevalent and it's hard to find good local sources of information so this has been invaluable.

    For our home, additional insulation is a very low hanging fruit. When we moved in, there was very literally zero insulation in the home and it would fall below freezing in many parts of the home even though the fuel oil furnace was running non-stop. Since then, we've replaced the windows and had cellulose blown in the walls and attic. We replaced the furnace with a GSHP five years ago and it has since heated the home with no problems even when it is far below zero. This year we are tightening up the exterior envelope and adding rigid foam and new siding to the exterior. There are currently places where the cellulose is falling out of the wall cavities because of cracks/damage in the old siding. I feel that this is also a pretty low hanging fruit. I completely understand that I need to have a professional perform the heat loss calculations. I am not guessing but simply wanted to pose the question to the forum to see if using this spare capacity was a reasonable approach to cutting the expense of an additional GSHP.

    Right now the plan is have the pool partially below ground with a thick layer of sprayed on foam. The edge of the pool would be level with the deck so the extra insulation will not show. I'd put it inside but this was a compromise. However, we are planning on purchasing a cover that creates a tight, foil faced seal for the top of the pool.

    We have radiant floors. Our plumbing and heating contractor felt it would was easier to running tubing rather than ductwork through the house and we were replacing the flooring anyway so it sounds like this might be an easy connection with a water-to-water system.

    I'm not sure we can add any additional PV panels. We are planning on adding a 20kw array with this remodel and I understand that there are some tax implications and/or net metering problems over the 20kw.

    Thanks for the help.

  8. charlie_sullivan | | #8

    If your heat pump is already producing hot water, it would be pretty easy to connect it to the pool through a flat-plate heat exchanger. Just winging it, against all the good advice to do load calcs, I'd bet that you'd have sufficient capacity, given the further upgrades you are making. It would actually be pretty low risk to simply set that up and try it. I'd set up the controls for the house to have priority over the pool in the case that the heat pump couldn't keep up. Then, worst case, the pool wouldn't get heat on the coldest days of the winter ... but I'm guessing your usage of the pool would be low on those days anyway. You wouldn't want to let the pool freeze, but if it dropped below a comfortable temperature that's OK. Just be sure the plumbing is run through conditioned space, because that would freeze a lot faster than the pool.

    When I suggest giving the house heating priority over the pool, I don't mean shutting off the pool heating any time the house is calling for heat. Rather you'd want controls that shut off the pool heating only if the heat pump buffer tank temperature got outside the range its thermostat is set for--that would be the indication that the heat pump couldn't keep up with the demand of both. Setting up controls to do that is slightly tricky. Choosing the right heat exchanger is also a little tricky. So you might need an engineer to spec those systems for your plumber, or a mechanical/HVAC contractor that would have that capability. But if that is hard to find in your area, we might be able to provide enough guidance for your plumber to do it.

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