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Community and Q&A

Gas or Electric Heating for Pool / Spa

user-789873 | Posted in General Questions on

I have a site in Texas that doesn’t have a gas line installed and we are putting in an approximately 1,300 SF pool with 75 SF being part of a heated spa pool.  The pool guy is telling me that a gas line needs to be run to the site to heat the pool because electric heat pumps won’t get hot enough to heat a spa pool and that only gas can achieve this.  Are electric spa/pool heaters not powerful enough to heat a hot tub/pool set up?  Extending a gas line to the property is an expensive proposition and electric heating seems like a safer and less carbon intensive route (depending on where the electricity is coming from).

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Replies

  1. Expert Member
    BILL WICHERS | | #1

    A typical hot tub uses an electric resistance water heater. You usually end up with somewhere around a 50-60A 240V circuit to feed such a hot tub, which covers the heaters and the pumps. This isn't a huge load, and can ususually be accomodated by a normal residential electric service.

    I'm not aware of any heat pump type heaters that can handle a large pool. You could probably get electric heaters big enough, but they will be electric resistance, and tens of kw, similar to on-demand electric water heaters, and very possibly will require an upgrade to the electric service to your home. This may be more expensive than a gas heater. I've always seen gas heaters for pool heating, sometimes using propane in areas where natural gas is available. I'm not sure you have much alternative here.

    Note that using electric resistance heaters instead of natural gas doesn't necassarily mean less fuel use. In many areas, electricity is sourced primarily from a mix of coal and natural gas, so using electric resistance heat ends up using MORE fuel for the same BTU output, after allowing for losses along the way (power plants aren't 100% efficient, etc.). Where electric can win in this regard is when using a heat pump, where you get more BTUs out per unit energy in, since heat pumps move energy instead of making it.

    Bill

  2. Expert Member
    AKOS TOTH | | #2

    The only issue is a pool that large will need a number of heat pumps. The temperature needed for a hot-tub is well within the capability of most heat pump pool heaters, getting one designed for colder climates which are capable of higher temperature lift can buy you some piece of mind.

    Depending on the size of the house and local availability, something semi commercial might make sense. The 5 ton LG multi V has a hydro kit (most likely you'll need at least 2) you can use as a pool heater but as a bonus it also does energy recovery which means in the summer time energy used to cool the house will also provide part of the heat for the pool.

    https://lghvac.com/commercial/product-type/model-details/?productTypeId=a2x44000003XR0O&modelId=01t44000008fw8M&modelNumber=ARUB060GSS4&iscommercial=true

  3. nynick | | #3

    What a crock of poo that pool guy is handing you. In Florida I had a pool/hot tub set up that was heated by electric. To heat the spa we needed to redirect the heated water directly to the spa for 45 minutes or so to get it up to temperature. The valves shut off the pool supply of heated water during this usage. After we were done I'd reopen the valve and the pool and spa would heat to a normal 80-82 degrees.
    No question the heater would struggle during cold weather but for the rest of the time it was never a problem.

  4. unremarkab1e | | #4

    We are in a similar decision-making stage. We wanted to make everything all electric in our house, and it turns out the one exception will be the outdoors with natural gas heater for the pool/hot tub.

    All the research (troublefreepool, pool forums) and the few pool contractors I've spoken to said that heat pumps would be a stretch for heating the pool and hot tub.

    I think it comes down to what your expectations and needs are. If you want an impromptu hot tub dip in October/November, a gas heater will be able to heat it much hotter and quicker than a heat pump. If you want to stretch your swimmable months into March and October, a heat pump can do that rather efficiently, but to temps of 80-82 like mentioned above. I don't think it'd be able to get to hot tub temps of 95-105.

    For us, my wife and kids wanted to be able to use the hot tub whenever she wanted and quickly, so natural gas it is.

    1. thedman07 | | #5

      You should also be sure to talk to them about what energy costs will be involved in how you set your expectations.

      If you want to be able to heat the whole pool in the dead of winter with a gas heater, you could be looking at a significant bill at the end of the month. We had a gas heater at my house when I grew up and we only used it once or twice because it consumed so much gas...

      If I were building a pool now, I would much rather have a heat pump based system that could extend usage of the pool into more of the year for a reasonable price instead of a gas heater system that I was reluctant to use because it costs so much to run.

      1. unremarkab1e | | #10

        Great point.

        I should have clarified my statement. Heating the whole pool with natural gas in a Texas winter or even in Spring/Fall is something we MIGHT do 1-2 a year, if that. By doing so, we would have to expect and accept a $300, $500, $700 natural gas bill for that month I’m sure. I will say that as a child growing up, I remember jumping into a heated pool in winter at family and friends parties, may only happened 2-3x, and I still remember those days fondly. I’m fortunate my parents indulged us in that experience a couple times.

        I’m hoping to instill some memories in my kids minds as well, even if it costs a pretty penny.

    2. Expert Member
      BILL WICHERS | | #6

      >"For us, my wife and kids wanted to be able to use the hot tub whenever she wanted and quickly, so natural gas it is."

      Maybe what you should do is set the hot tub up to run all the time, but let the big pool use less heat. This way you could run the hot tub year round, and only heat the big pool during pool season. This would save you a lot on heating costs too. Most hot tubs I've seen are insulated, and they are setup to maintain toasty hot tub temperatures ALL the time, so recovery time isn't an issue. These setups have always been electric resistance, at least all the setups I've seen have been. This would be relatively easy to setup, and wouldn't need gas service. The hot tub part should be easy.

      The outdoor pool is really the tricky part. If you want rapid recovery, which means the ability to warm the pool up "quickly" (note that "quickly" is still going to take a while, it takes a lot of energy to heat a large mass of water quickly), then gas is probably your only practical option. If you want to keep it a little warm all the time, the heat pump option Akos recommended might be a good option. The heat pump's downside is that it will be good for keeping the pool warm all the time, but it is only around 64k BTU for heating, so it's not going to be good to warm the pool up quickly if you don't keep it warm all the time. Gas fired pool heaters I've seen have been in the hundreds of thousands of BTU range, so significantly larger, and they STILL take a while to warm up a cold pool.

      I would go with a packaged hot tub with electric resistance. This is simple, and standard, and doesn't require gas service. For the large pool, I think your options are either keep it warm all the time with the heat pump, or go with a gas fired heater if you want to be able to cycle it. Either way, if you decide not to run the large pool all year, you will have less issue heating it.

      Bill

      1. user-789873 | | #7

        Great summary Bill. I appreciate everyone's comments! It's given me a lot to think about.

      2. unremarkab1e | | #11

        Bill,

        I appreciate your thoughtful response.

        We do want the hot/tub spa to be attached to the pool, so a standalone hot tub is not an option. It does make a certain amount of sense, I understand that.

        Another issue is finding a reputable local pool builder who has used heat pump heaters and may be OK going out of their comfort zone.

        A lot of the conversations I’ve had were “OK, we can do this, but it may not get up to temp, it may take too long, it may not perform like you expect it to. Most of my clients go natural gas.”

        I think if I can convince myself with a heat pump to keep the hot tub ~80-90 year round, solar cover in the winter, that way it hopefully only takes 2-4 hours to get to 104F if I plan ahead.

        1. Expert Member
          BILL WICHERS | | #12

          What is the VOLUME (gallons) of the pool+hot tub combo? From that info, and the BTU input from the heat pump, you can calculate the time it will take to raise the temp from 80F to 104F using the heat pump. I can run the calcs for you if you can provide the water volume of the pool and hot tub.

          Bill

  5. billfrombirchwood | | #8

    Calculate the BTU required for a cold water fill and BTU required to maintain the temperature.
    Size the heat exchanger and then size the heat pump.. the calculate cost for a NG and cost for electric. Here in Minnesota, I am looking at moving to a heat pump next time I replace the electric resistance heat.

    1. mgensler | | #9

      I agree with what Bill has said. We have a prepackaged electric hot tub from Hot Springs. We usually only use it in the winter regularly but keep it filled and the temp turned down in the summer. We have a gas heater on the pool but only use it maybe 2x per year when we have a party. We're in zone 4a so quite a bit cooler than TX. Personally, I would skip the pool heater and see how it goes. You can always add it later. Just pour the pad large enough to accommodate it now.

  6. benwolk | | #13

    Arctic Heat Pumps claims to have a pool/spa compatible heat pump and it looks like their largest capacity unit goes up to 88k BTU of heating: https://www.arcticheatpumps.com/inverter-pool-heat-pump-specification.html

    I would reach out to them with your location and pool specs to see if their equipment can serve your needs.

    I also would think that possibly a Sanden CO2 heat pump water heater would be able to be adapted to provide the heating required. I know that they can produce water way hotter than the 104 degree F that you want for a spa, but not sure how the sheer volume and/or GPM needed for a spa and pool would work with their units.

    Since you are in Texas, have you looked at solar hot water heating? That's a low cost and low tech way to heat your pool and spa. It could be added as a supplement to a heat pump to lower the demand on the heat pump. Solar hot water can easily reach temps above 140F.

    1. unremarkab1e | | #19

      I did find the arctic heat pump website the other day. It was hard finding a local distributor in Texas, much less an installer from their website.

      I've found builders/contractors have been very hesitant to use an "unknown" product for many reasons, lack of experience, risk of poor performance, unmet expectations, etc.

      I wish there was a way to compare the performance for certain metrics. Such as, same size hot tub, how long does it take to raise temp from 78F to 104F with XXXXX BTU heat pump vs XXXXXX natural gas heater. Alas, everyone's pool design/hot tub design is different, different climates, different locations, different temps makes it hard finding some good objective data.

      1. Expert Member
        BILL WICHERS | | #20

        >"I wish there was a way to compare the performance for certain metrics. "

        There IS a way! If you only want a RELATIVE measurement between the two, then it's REALLY easy: if one heater is three times the BTU output as the other, then the bigger BTU output can heat up the pool three times faster. Easy. You can scale that to any size heater, if one heater is 60kBTU and the other is 80kBTU, the 80kBTU can heat up your pool about 33% faster than the 60kBTU unit.

        If you want to know an ABSOLUTE measurement, such as how long it will take to go from 78F to 104F, then you need to know how many BTUH you need (note the "H", which is for "hour", as in "BTUs PER HOUR") to raise the VOLUME of water you have have by 26*F. That's easy too, but you need to know the volume of water in your pool first. After that, you can use the specific heat of water to work out how long it will take to heat that pool that much with any size heater you want to check. If you can provide the volume of your pool, I can show you an example calculation.

        Bill

  7. DennisWood | | #14

    Gas and electric prices are looking to nearly double this winter. I suspect you’ll see solar with a decent ROI as part of this solution. Folks are on equal billing have already seen a 70% jump in NG. Electricity costs are on the same trajectory.

    1. Expert Member
      BILL WICHERS | | #21

      In my area, gas costs have risen much faster, since the gas co adjusts pricing monthly based on their supply costs. Electric costs rise much more slowly, since they aren't as dependent on short term market pricing. In some cases, that may mean a heat pump could potentially be even cheaper to operate than you might think, but you need to know how your utility's cost structure works to know for sure.

      Just as an FYI, my local gas price is about 94% higher this month than it was for this month last year (I keep track). I have a number of air sealing and insulating projects I hope to complete over the next month or so that will help with that, and since I bought the materials a while ago, I'm on a mission to get'em installed now to deal with those spendy gas prices!

      Bill

  8. hughw | | #15

    I'm a member of the Planning Board in the town of Chilmark on Martha's Vineyard. We're currently working on a revision to the Zoning byaws that would mandate the use of either onsite produce energy or heat pumps for pools and spas. As far as I know, there is no reason that a heat pump shouldn't be capable of doing the job, although I haven't run the numbers. Search the internet for articles like this https://buildahottub.com/the-ultimate-guide-to-air-source-heat-pumps-for-hot-tubs/

    1. Expert Member
      BILL WICHERS | | #16

      The issue is with output capacity. Heat pumps tend to be relatively low BTU output, with the idea that they'll run in modulating mode all the time, so a relatively small amount of heat output over a relatively long period of time. Typical gas/electric heaters tend to be much higher BTU, with the idea that they'll cycle on and off to maintain a target setpoint, so they put out a relatively high amount of heat for a relatively short period of time.

      This isn't usually a problem to MAINTAIN temperature, but it can be an issue to RAISE temperature, such as if you want to keep something cool when you're not using it, but get it warm quickly when you want to start using it. A regular high-BTU heater can put in more heat over a shorter period of time, so you can warm something up relatively quickly. Heat pumps are usually more suited to MAINTAINING a constant temperature, so they aren't usually as good at heating things up quickly. This is why it's generally not recommended to use setback thermostats with heat pumps, for example.

      Now you could put in several heat pumps I suppose, but that's usually not a desireable option. It really all comes down to how many BTUs do you need, and how quickly do you need them. I would advise againt mandating any particular system as that can often run into unintended consequences. A better option may be to set some design standards, or to use heat pumps for steady state temperature maintenance while maintaining conventional heaters for rapid temperature cycling, the best of both worlds, in a sense.

      Bill

  9. walta100 | | #17

    In terms of dollars and cents city gas is generally cost less per BTU give the huge number of BTUs requite for this luxury gas seems like a winner.

    Run the numbers but keeping a pool above say 85° all year is a bigger bill than I could stomach.

    Walta

    1. Expert Member
      AKOS TOTH | | #18

      Not necessarily.

      For example, my current natural gas cost (minus meter fee) including all taxes and charges works out to about $0.06c/kwh. At my current electricity cost (again including all fees and taxes) is $0.15/kWh so any heat pump with a COP greater than 2.5 is cheaper to run. Most heat pump pool heaters in milder climate will hit a COP north of 4, even in my colder climate, a heat pump would win on operating cost by a good margin.

      Where gas wins is on raw power, a 400000BTU/h fuel burner costs peanuts, the same size heat pump is real money. In the case of the OP, if they have to spend money on getting gas run, a heat pump can work out cheaper in the end. My suggestion would be to design the system to reduce losses when not in use such as building in a solar cover.

  10. mikeyouse | | #22

    I'm in the upper Midwest and bought a 140k BTU heat pump from Inyopools this Spring. I installed it myself and it did an amazing job heating my pool all year. It's a weird sensation since the return to the pool is only ~10º warmer than the supply to the heater, but it will do that all day and all night (if it's above ~50º outside). We kept our pool at 85º all summer and had it running into late September with no issue.

    My primary concern was sizing as well, our pool is almost twice as large as it should be (50,000 gallons) and the 140k BTU heater was smaller than all of the calculations suggest but like you, I didn't want to run a new gas line and have a new gas-burning appliance. Our electricity costs were fixed this year at $0.115/KWh so my bills never really exceeded $300/month even when it ran a lot. The most important thing in terms of an undersized pump is to make sure you have a solar cover on to limit evaporative heat loss - DOE estimates almost 90% more energy consumption on an uncovered pool compared to a covered one.

    (The one I went with: https://www.inyopools.com/RecommendedProducts/R8450TI-E)

    Let me know if you have any questions, I'd be happy to let you know any details.

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