# Pool heat pump - How many BTUs?

On Wednesday, May 22, 2013 9:46:55 PM UTC-4, snipped-for-privacy@gmail.com wrote:

he correct unit for my needs (an Aquacal TropiCal) puts out 112,000 BTUs (4 0 amps/5.8 KW). I'm thinking that a larger unit that puts out 141,000 BTUs (50 amps/6.4KW), would heat the pool quicker and require less time on, thus use, in theory, less electricity - but it's about \$500 more expensive than the small unit. We'll probably only use the pool on the weekends. Not sure how long it will take to break even on this with running it for only a cou ple days per week. Anybody have any thoughts or opinions about this? Is my thinking skewed? Is it worth the extra cost? Thanks!
1 btu raises 1 gal of water 1 deg so do the math.
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On Thu, 23 May 2013 14:05:03 -0700 (PDT), jamesgang

correct unit for my needs (an Aquacal TropiCal) puts out 112,000 BTUs (40 amps/5.8 KW). I'm thinking that a larger unit that puts out 141,000 BTUs (50 amps/6.4KW), would heat the pool quicker and require less time on, thus use, in theory, less electricity - but it's about \$500 more expensive than the small unit. We'll probably only use the pool on the weekends. Not sure how long it will take to break even on this with running it for only a couple days per week. Anybody have any thoughts or opinions about this? Is my thinking skewed? Is it worth the extra cost? Thanks!

Then the issue becomes, how much do you lose to the air, not as simple a calculation.
When the hottest water concentrates at the top, this ends up being a bigger part than simply the volume and the BTU. With that 330k btu heater, my water stratifies to the point that it feels great at the top but it is cold at the bottom. A 1HP pump can't keep up with convection.
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the correct unit for my needs (an Aquacal TropiCal) puts out 112,000 BTUs (40 amps/5.8 KW). I'm thinking that a larger unit that puts out 141,000 BTU s (50 amps/6.4KW), would heat the pool quicker and require less time on, th us use, in theory, less electricity - but it's about \$500 more expensive th an the small unit. We'll probably only use the pool on the weekends. Not su re how long it will take to break even on this with running it for only a c ouple days per week. Anybody have any thoughts or opinions about this? Is m y thinking skewed? Is it worth the extra cost? Thanks!

The other piece necessary is that heating eqpt is rated in BTU's per hour, so a heater with 100K BTU output rating, should raise the temp of 100,000 gallons of water one degree in one hour. I don't know how heat pump units are rated, but with gas fired units, the BTUs are typically the INPUT energy, so you have to decrease that by the efficiency of the particular unit. If a 100K unit is 80% efficient, then it's putting out 80K btus.
The big unknown is the rate of heat loss of the pool and that is going to slow down the heat rise.
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wrote:

e:

at the correct unit for my needs (an Aquacal TropiCal) puts out 112,000 BTU s (40 amps/5.8 KW). I'm thinking that a larger unit that puts out 141,000 B TUs (50 amps/6.4KW), would heat the pool quicker and require less time on, thus use, in theory, less electricity - but it's about \$500 more expensive than the small unit. We'll probably only use the pool on the weekends. Not sure how long it will take to break even on this with running it for only a couple days per week. Anybody have any thoughts or opinions about this? Is my thinking skewed? Is it worth the extra cost? Thanks!

Well shiver me timbers...... James made a mistake and I didn't catch it. A btu is not the amount of energy to raise one gallon of water one degree. It's the amount of energy to raise ONE POUND of water one degree F.
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On Thu, 23 May 2013 14:05:03 -0700 (PDT), jamesgang

correct unit for my needs (an Aquacal TropiCal) puts out 112,000 BTUs (40 amps/5.8 KW). I'm thinking that a larger unit that puts out 141,000 BTUs (50 amps/6.4KW), would heat the pool quicker and require less time on, thus use, in theory, less electricity - but it's about \$500 more expensive than the small unit. We'll probably only use the pool on the weekends. Not sure how long it will take to break even on this with running it for only a couple days per week. Anybody have any thoughts or opinions about this? Is my thinking skewed? Is it worth the extra cost? Thanks!

No, it's about 1/8 that. A btu is the amount of heat it takes to raise a POUND of water 1F. ~8.3 pounds per gallon.
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the correct unit for my needs (an Aquacal TropiCal) puts out 112,000 BTUs (40 amps/5.8 KW). I'm thinking that a larger unit that puts out 141,000 BTU s (50 amps/6.4KW), would heat the pool quicker and require less time on, th us use, in theory, less electricity - but it's about \$500 more expensive th an the small unit. We'll probably only use the pool on the weekends. Not su re how long it will take to break even on this with running it for only a c ouple days per week. Anybody have any thoughts or opinions about this? Is m y thinking skewed? Is it worth the extra cost? Thanks!

I think you'd better go back to school 1 btu raises 1 pound of water 1 degree F
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snipped-for-privacy@gmail.com wrote:

paint pool a dark color and get a clear pool cover
use your existing system for additional input
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On 5/23/2013 7:08 PM, Malcom "Mal" Reynolds wrote:

The OP could get a solar blanket but they do tend to deteriorate quickly in chlorine pools.
The last thing he should get is an electric pool heater unless he just isn't concerned about money. I'm surprised they sell them and anyone would buy one.
If I just had to have a heated pool in his situation, I'd consider a solar heater, or do the cost analysis of getting a propane tank. A propane tank may cost a lot up front but, the electric heater is going to cost a lot more in the long run. I had a electric spa and got rid of it after one season. I have a gas heater for my pool/spa now and love it. I don't think the OP understands what it takes to heat a pool.
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It's not a purely electric heater. It's a heat pump. And just like you can heat a home with them economically in some parts of the country, apparently you can also heat a pool. It depends on what the options are and what the cost of electricity is.
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In article

maybe he should just dump the heat from his house heat pump into the pool (assuming that's how he cools the house) I know it won't provide all the heat but it should provide some and at no additional cost other than the initial set-up
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On Thu, 23 May 2013 20:15:44 -0700, "Malcom \"Mal\" Reynolds"

I stop heating the pool before I turn on the A/C. I suppose climate might change that
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On May 24, 5:19 am, snipped-for-privacy@aol.com wrote:

A lot of it would be down to the Coefficient of Performance of the heat pump. X4 is typical but they have improved a lot lately. I would have thought one that size would need three phase supply, But whatever you do, you need to minimise losses (pool covers etc) first so that the smallest possible plant is needed.
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On Thu, 23 May 2013 22:13:35 -0700 (PDT), harry

We just use bigger wire and single phase units unless it is a commercial installation.
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On 5/23/2013 10:13 PM, harry wrote:

it is nearly impossible to get 3 phase power at a house in the US. utility companies don't run this in residential areas, only in commercial areas. if it was even somewhere in the neighborhood, it would cost 10's of thousands of dollars to have it run even a few blocks.
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On May 24, 12:19 am, snipped-for-privacy@aol.com wrote:

I agree that is one of the obvious problems. Dumping that home AC heat into the pool could help, but when you look at the whole situation, it doesn't make much sense to me. Among the problems:
As you point out, heat is not available when you need it most. And when the most heat is available you need it least, or not at all. The OP is in FL, which would be one of the worst climates with regard to that.
Typical home AC is maybe 4 tons, or 48K BTUs. And that is when it's actually runnning. On days that are just modestly hot, when you'd typically want to heat the pool, what percent of the time is it actually running? 20%? So, now you're down to 10K btus. Typical pool heater is 100K to 400K btu
To try to roll your own is not a trivial task. And the one system available, that was shown on This Old House, requires cutting refrigerant lines to install the additional water based heat exchanger, modifying the existing system, recharging it, etc. All that isn't cheap and I'll bet you can kiss your warranty good bye. For the same amount of money, you could buy a solar system, which, if you have the space for it, IMO, is a much better option.
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On 5/23/2013 9:31 PM, snipped-for-privacy@optonline.net wrote:

I see. My mistake. Interesting.
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