Heat Pump or Gas in Austin Tx

Go online to the Pentair website. Under there pool heater section they a cost comparison calculator for heatpump versus gas (NG or propane). It will give you a good cost comparison fir your area as it uses local and regional data for utility costs.

Pentair has a Heat Pump Calculator to determine the appropriate size Heat Pump for your location. Pentair seems to do honest calculations based on the physics and efficiencies of each type of pump and energy source.

To get the most accurate cost comparison you should change the default electric kwh, natural gas price, and propane price to actual prices in your area.

I don’t think the cost differences will be dramatic. The cost of heating a pool is influenced much more by how you operate the pool than the source of the energy (unless there’s a huge disparity in utility costs which isn’t typical). If you are diligent and cover a pool or spa every night so that there’s no evaporative heat loss and you don’t run your pump in such a way as to encourage heat loss, then either method is going to cost roughly the same. So, in many instances, the choice of heating source comes down to what you want to achieve. If you’re a die-hard spa user and you need that attached spa to heat up quickly, then gas is your best option. If you can afford to wait and don’t need the spa to get too hot, then HP is an option. In the heat of the summer months people rarely need to use their pool heaters (unless the pool is shaded a lot) so if you’re trying to get extra swim days in the shoulder months, a gas heater will get you there quickly but a HP running all the time may cost less.

Keep in mind that a heat pump is going to need its own dedicate 240V/60A circuit and so there’s going to be added installation cost beyond the cost of the heater.

I live in Austin, serviced by Texas Gas Service. I have a Pentair 400k BTU gas heater. I calculated it costs me $1.75/hour to run it. I have a 19,000 gallon pool and a 1,000 gallon attached spa. I can raise the temp of the spa about 1 degree every 1.5 mins and the pool 1 degree every 30 mins.

I understand heat pumps to be more "slow and steady" vs gas which is more instant. If you truly will be running your heater every day, that would not be the norm but a heat pump may be your best bet. Most people around here will use their gas heater to heat the spa and maybe kick it in the pool every so often for special occasions or to add a few degrees in the spring or summer.

Also keep in mind that Pentair sells both gas and heat pumps, so in theory they are not biased in their heat pump recommendation.

That doesn't sound unreasonable. I did an initial look things in my area, and gas was recommended. But we have a short, cool season where extending the swimming season means you're operating the heat pump well outside it's optimal temp range, so NG wins on cost.

For a warm area like Texas, it doesn't surprise me in the slightest a heat pump is more economical to run.

If you know your specific utility rates (they should be listed on your bill, but be sure to add up all "per unit" costs as many bills split up distribution and supply costs but charge per kWh/therm for both), then you can re-run the calculator and enter your exact utility rates. There's an option to do that somewhere.

No one swims in Feb, that’s just too early. Cut off the shoulder months to March and October and you should see a more realistic number. Your pool is going to get used the most when the kids are out of school. I have found that when school starts up, pool use drops off like a stone .... and school starts in mid-August here in Tucson!!! So I wind up maintaining a swimmable pool for months with very little use (weekends only).

I would say this - if you plan to use the spa a lot and want fast heating, you’ve got to go with gas. You will get super-frustrated in short order by having to wait 60-90 mins for the spa to heat up.

jimbethesda said:

I live in Austin, serviced by Texas Gas Service. I have a Pentair 400k BTU gas heater. I calculated it costs me $1.75/hour to run it. I have a 19,000 gallon pool and a 1,000 gallon attached spa. I can raise the temp of the spa about 1 degree every 1.5 mins and the pool 1 degree every 30 mins.

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Man, this is great info. I live in Austin, TX as well and have the same heater. My pool is 18.5k gallons with a small spa.

This will be my first winter with a pool.

When you say $1.75/hour: Do you multiply that by 24 hours to get the full day? Then times ~30 days to get the month? If so, that gets me to $1,260/mo. Or do you run it less than 24 hours a day? Thank you in advance!

Heat Pump vs Gas comes down to the same thing - how much does is cost to provide X amount of BTUs. Gas is easy - 1 MCF of gas will give you roughly 1,000,000BTUs, given 100% efficiency. Most gas heaters are around 80-85, so you're basically looking at 1MCF = 850,000BTUs, and 1MCF is around $9 (your local price may vary).
Heat pumps lose efficiency as the outside air temp drops - but as NewDude suggested, most people don't swim November through February. February here, the water is solid, so it's not really a consideration !
Its also really hard to pin down any concrete numbers on heat pump costs/btu, partly due to the way they work. The best 'ballpark' I could find was roughly 20,000 BTUs/kW = so at 10c / kwh, 850k would be $4.35. I can't vouch for that number, because I can't really find anything definitive. If its warmer outside, they are more efficient - on a cold day (when you want the heat) they are less efficient.

There was a post here that had some math and reference to a table, but that table is no longer available
Natural Gas heaters are generally cheaper than heat pumps too - sometime significantly so.
So, assuming you have the headroom in your electrical supply, a heatpump is probably more efficient - but is probably slower than a gas heater - and probably more expensive too.

For what it's worth, here in MI we went with the gas heater - it was just about half the price of the heat pump, (~3.5k installed for 250K BTU).
Also, its worth remembering that once the water is warm, you're only paying to keep it warm, and that number is much smaller than the initial heatup cost. my July usage for the pool I figure came out to roughly $1/day. That's less than 1/4 the cost of the Liquid Chlorine I'm adding

SJPoe said:

Heat Pump vs Gas comes down to the same thing - how much does is cost to provide X amount of BTUs. Gas is easy - 1 MCF of gas will give you roughly 1,000,000BTUs, given 100% efficiency. Most gas heaters are around 80-85, so you're basically looking at 1MCF = 850,000BTUs, and 1MCF is around $9 (your local price may vary).
Heat pumps lose efficiency as the outside air temp drops - but as NewDude suggested, most people don't swim November through February. February here, the water is solid, so it's not really a consideration !
Its also really hard to pin down any concrete numbers on heat pump costs/btu, partly due to the way they work. The best 'ballpark' I could find was roughly 20,000 BTUs/kW = so at 10c / kwh, 850k would be $4.35. I can't vouch for that number, because I can't really find anything definitive. If its warmer outside, they are more efficient - on a cold day (when you want the heat) they are less efficient.

There was a post here that had some math and reference to a table, but that table is no longer available
Natural Gas heaters are generally cheaper than heat pumps too - sometime significantly so.
So, assuming you have the headroom in your electrical supply, a heatpump is probably more efficient - but is probably slower than a gas heater - and probably more expensive too.

For what it's worth, here in MI we went with the gas heater - it was just about half the price of the heat pump, (~3.5k installed for 250K BTU).
Also, its worth remembering that once the water is warm, you're only paying to keep it warm, and that number is much smaller than the initial heatup cost. my July usage for the pool I figure came out to roughly $1/day. That's less than 1/4 the cost of the Liquid Chlorine I'm adding

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Thank you for the information. Looks like I pay $10/mcf for natural gas. I ran this Raypak calculator online. Looks too good to be true to heat for 6 months in winter (mind you, its Texas, so doesn't get super cold) for only $2,381. Is this actually possible though? My heater is 400k BTUs and pool is 18.5k gallons.

A heat pump heats much more slowly than a gas heater. If I'm going to have a swimming party, I'll start the heat pump at least the day before. I'll use the heat pump for a few days in the spring and fall to warm up the water a few degrees, and that makes a big difference. I don't have a spa, but if I did I'd definitely have a gas heater. Several heat pumps are reversible and can chill your water in the summer. We've chilled the water several times this summer and it's great.

pjt said:

A heat pump heats much more slowly than a gas heater. If I'm going to have a swimming party, I'll start the heat pump at least the day before. I'll use the heat pump for a few days in the spring and fall to warm up the water a few degrees, and that makes a big difference. I don't have a spa, but if I did I'd definitely have a gas heater. Several heat pumps are reversible and can chill your water in the summer. We've chilled the water several times this summer and it's great.

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That’s pretty cool. I wasn’t given the option of a heat pump, likely because I have a spa, but it sounds like a really economical way to heat your pool.

Geophffrey said:

That’s pretty cool. I wasn’t given the option of a heat pump, likely because I have a spa, but it sounds like a really economical way to heat your pool.

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Economical … maybe. Heat pumps are basically air conditioners run in reverse. So they use a lot of electrical energy to move heat around. For heat pumps, the spec to look at is the Coefficient of Performance (COP) which is basically the ratio of the heat energy generated to add to the water divided by the electrical energy used to create and move that heat. If the atmospheric conditions are right, the COP can be 6 or higher. Of the temperatures and humidity are not optimal, the COP can actually be negative. The COP varies with temperature and humidity since moist air can hold more heat energy and warm air provides the heat to the pool water. Once the air temperatures drop below 70F, the COP begins to fall and the heater is not very efficient at all.

Gas heaters, by contrast, derive all their energy from the combustion process. So it doesn’t matter as much what the outdoor temps are except for the fact that you don’t really want to run a gas heater cold as the condensate generated from the combustion gas can be very corrosive.

JoyfulNoise said:

Economical … maybe. Heat pumps are basically air conditioners run in reverse. So they use a lot of electrical energy to move heat around. For heat pumps, the spec to look at is the Coefficient of Performance (COP) which is basically the ratio of the heat energy generated to add to the water divided by the electrical energy used to create and move that heat. If the atmospheric conditions are right, the COP can be 6 or higher. Of the temperatures and humidity are not optimal, the COP can actually be negative. The COP varies with temperature and humidity since moist air can hold more heat energy and warm air provides the heat to the pool water. Once the air temperatures drop below 70F, the COP begins to fall and the heater is not very efficient at all.

Gas heaters, by contrast, derive all their energy from the combustion process. So it doesn’t matter as much what the outdoor temps are except for the fact that you don’t really want to run a gas heater cold as the condensate generated from the combustion gas can be very corrosive.

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I don't think anyone would be swimming if a pool heat pump had a negative COP. It takes a lot to bring even old, inefficient heat pumps to a negative COP. From what I've read, I can probably expect the heat pump at my current rental (there's no gas to my rental unit) to be around 1.5 even in the 20's °F ambient. Modern (house heating) heat pumps can maintain positive COPs to -10 °F or below. (of course this is considering a typical house at 68 °F, and pools are heated higher than that)

I have a friend here in Madison, who's considering getting rid of (natural) gas in his house and going with air source heat pumps. I did some research for him literally just now, and concluded that operating cost wise (not counting equipment, install, and maintenance costs), he'd probably break even compared with his 80% efficient gas boiler when switching to a very high efficiency air source heat pump. Yes, I did those calculations for up here in Madison, WI.

This was based on a heat pump being able to obtain an average COP of about 2.25 at an average daily temp of 20 °F (our average daily temp for January), and 2.5 at 25 °F (Dec and Feb). At a COP of 2.5, and our current prices the operating cost is a break-even between a heat pump and his 80% efficient gas boiler. So for this example, with a very high efficiency heat pump, compared to an 80% efficient gas heat here in Madison, you actually end up only paying more in January, break even in Dec and Feb, and have cheaper heating in Mar, Apr, Oct, and Nov.


Average temps here in Madison:


COP vs average daily temps from a test house in Connecticut, for a very high efficiency air-source heat pump:


Obviously this is a very high efficiency air source heat pump, and pool models are simpler, single stage fixed speed pumps. But it looks like the Raypak models get a COP of 4 at 50 °F ambient, 80 °F pool water still. At my rates (and this will vary wildly), as mentioned above, you only need a COP of 2.5 to break even in operating cost between a heat pump and an 80% efficient gas heater, which would be typical of a gas pool heater.

Now, the big thing here, besides local rates, is that a 400 kBTU gas heater can heat a pool much faster than a 120 kBTU heat pump, so you can heat as-needed much more easily, and heat loss is proportional to water temp, so shutting off between uses (like any heating application) will always save money. So for most people they'd be better off with a gas heater and heating on-demand. But for those that want a pool always ready to swim, it's probably going to be difficult to beat a heat pump.

The other thing is rates vary a lot. For pure heat component (not accounting for efficiencies), right now with my rates gas is 1/3 the cost of electric. When I calculated this a couple years ago, it was 1/5th, which changes the equation a lot.

I wonder how long until pool heat pumps start getting variable speed compressors.

jseyfert3 said:

I wonder how long until pool heat pumps start getting variable speed compressors.

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As soon as the pool equipment manufacturers can find someone dumb enough, I mean, willing enough to pay even more money than would for the regular model Residential HVAC equipment is always going to be better/faster/more-efficient/etc than pool equipment ever will be because the markets are completely different. But when it comes down to it, cash is king and price/cost will always be the dominant factor. They can make the most technologically spectacular product in the world and it won’t matter one bit if it isn’t within the ballpark of what yesterday’s tech cost, early adopters and technical enthusiasts aside.