I've gambled on a Aquastrong 120v Pool Heater for a 4500gal AGP. Thoughts?

In my example the wattmeter would have reported 4000 total watts over 2 hours (yes, about 2000watts/hour or 4kwh in popular jargon).
You can only report total energy used, not total power used.

Watts is power and kilowatt-hours is energy.

It is not an irrelevant pedantic point.

If you are teaching science formulas, you need to get the units correct.
I cannot claim to have found exactly how folks figured out that 1 BTU/hour “loses those units” to become 3.413 watts
btu/hr is a unit of power and watts is also a unit of power.

1 btu = 1055.06 joule.
1 hour = 3,600 seconds.
1 btu/hr = 1,055.06 joules/3,600 seconds.
1 btu/hr = 0.293 joules per second = 0.293 watts.
1 watt = 3.412 btu/hr.
1 watt-hour = 3.412 btu.

Energy can be measured and reported in many different units.

The primary unit of energy in the International System of Units (SI) is the joule (J), but other units like kilowatt-hour (kWh), calorie (cal), and British thermal unit (Btu) are also commonly used.

Power can be measured and reported in any units of energy divided by any units of time.

For example, calories per decade, joules per second, joules per minute, btu per week etc.

The watt (symbol: W) is the International System of Units (SI) unit of power, representing the rate of energy transfer, equal to one joule per second (1 J/s).

To get the C.O.P, you can divide Power Delivered by Power Consumed or you can divide Energy delivered by Energy consumed.

The main thing is to use consistent units for the numerator and denominator.
 
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115 volts x 18 = 2070 watts.

2070 watts = 7063 btu/hr.

35,000/7,063 = 4.95 C.O.P.

The calculations you suggested, @JamesW in post #29 are, in my opinion, flat out wrong, sorry to say – using juxtaposed inputs and incorrect use of the COP formula.

You went awry, I believe, when you used “consumed electrical watts” to back into the BTU/hr for the COP numerator, that presumes all the input electrical energy goes toward heating, which of course is not the case and corrupts the very meaning of COP – which is to tell us how much heat energy actually went into the water per unit of electrical watts consumed.
If you measure Power (or Energy) delivered to the water divided by the Real Power (or Energy) used by the Heat Pump, then that is the Coefficient of Performance.

You can use Power or Energy as long as you use consistent units for both.

If the Heat pump uses 115 volts x 18 amps x 0.9 (power factor), then that is 1,863 watts, which is equal to 6,357 btu/hr.

If the water gains 35,000 btu/hr, then that is a Coefficient of Performance of 5.5.
 
Thank you @nuttyp and @JamesW for your passion and expertise in this thread. I would be lying if I said I understand it all! I was skeptical about the COP claim from Aquastrong, so it's nice to know that it's likely BS. But it does sound like it will be able to accomplish my hope of topping up the heat in the pool, less likely to be able to extend the season. Once I get my pool setup and the power cord for the heater, I hope to be able to give some actual usage numbers to compare against. Thanks again and stay tuned!
 
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You’re welcome @DigitalGuru – thanks for acknowledging the efforts.

In my haste I did make this sloppy statement: “In my example the wattmeter would have reported 4000 total watts over 2 hours (yes, about 2000watts/hour or 4kwh in popular jargon)”. That didn’t look right even as I wrote it, LOL. That should have read “In my example the wattmeter would have reported 4000 total watts total watthours over the 2 hours (ie 4kwh)”. I made the edits in posts 29 and 40.

For now @JamesW and I remain in disagreement, and in a way I think we might both be missing the mark. I’ll try to clarify when time permits. In the interim, will look forward to hearing about your experience.

“Extending the season” is an interesting phrase. I tend to think that any amount of heat extends the season even if only by a bit. And of course every season comes and goes with variation.

Peace brothers!
 
Hello all. Got the pool setup this weekend, heater and all! Much faster this year compared to our first last year. Was filling within 90 minutes, with a couple breaks. I waited until we had about two feet of water before I started on the wall skimmer install. I decided to not cut the butterfly gasket. I marked the openings and screw holes from the outside using the face plate as the template. Used a drill to makes the screw holes and a sharp razor for the main opening. Installed gasket, pre-screwed the screws through the face plate, gasket, liner, gasket before lining up the skimmer. Tighten down and no leaks! Once I got the 8ft ground rod driven in the ground and a 8ga copper ground wire for the heater, I was able to turn it on this morning. A first,it would trip the GFCI outlet that it was plugged into. That outlet is only a year old, so I was concerned this unit might pull more than listed, tripping the outlet. But I went to HD and bought a replacement GFCI and a regular one for testing. The new GFCI outlet worked great! The heater is now running with a 2-3 deg difference between the inlet and outlet. Unfortunately this unit is pretty dumb/ doesn't have any power information accessible in it's screen or web app. I'll have to check my electric usage website for details in a few days as that is a couple days behind my change in consumption. The app did find the unit easily with Bluetooth and synced with the app seamlessly. There some language issues in both the manual and app interface, so it takes a bit to understand. So far so good, the heater is running on the same circuit as our garage door opener and garage lights and that was my main concern, that the garage door opener would trip the breaker. So win for that!
 

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I'm sure we appreciate your follow-up and I'm glad to hear the heater works. But I hope you are considering far more about electrical safety - ie to save a life - than the couple things you alluded to in the recent post. I would urge you to have an electrical inspection by someone qualified and knowledgeable in pool electrical bonding and in general. Firstly, it is improper to deem a circuit 'okay' just because it stopped tripping breakers. Your GFCI outlet and circuit should be sized based on the manufacturer minimum circuit amperage (which we also know was wrong in their manual). Also, that circuit is usually dedicated to one high-current device like a heater, not shared with other devices eg garage door opener. While you're at it, please consider the length and gauge of the circuit wire including any extension cords in play. And the GFCI outlet should be tested with a GFCI tester - for all we know the first one was the one that tripped properly and something is wrong with the new one or how it's wired. Bonding is another matter for serious consideration, as a simple #8 wire to a "grounding rod" is hardly adequate. The use of the grounding rod itself is questionable, allowed in some rare cases, but I have much less experience with above ground pool scenarios. At the very least, all metal parts within reach of the pool, including structures, pumps, heaters and lights need to be bonded together. I understand there are (or were) code exceptions in the case of storable pools, so others may chime in, but yours does not appear all that 'storable' anyway. Further reading on pool electrical safety is all over TFP and the internet, examples including Bonding an above ground pool, also How To Bond An Above Ground Pool? Follow These Simple Steps! and www.mikeholt.com/pools. Sorry to harsh your mellow, but please be safe!