What's your current pool temp?

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A BTU is the amount of heat needed to raise one pound of water one degree Fahrenheit. 4800 gallons of water is about 40,000 pounds to that would be 1.5*40,000 = 60,000 BTU/hr.

That is net of the heat loss from evaporation and conduction. The worst-case evaporation assuming 0% humidity and 8 MPH wind at the surface of the pool with water temp of 88ºF and air temp of 83.5ºF is 422 BTU/hr/ft2. 15' round would be 177 square feet so 75,000 BTU/hr loss. Obviously with the net gain you had, you didn't have this worst-case loss, most likely because the wind at the surface of the water wasn't 8 MPH. At 0 MPH, the loss is 93 BTU/hr/ft2 so 16,500 BTU/hr.
 
Thanks, chem geek!

I used about 30' of 3/4" copper tube to make that exchanger, as a "proof of concept" rig. 3/4" headers, with (6) 3/4" runners set in three layers. I'm actually surprised it's lasted this long.

I'm getting ready to try again on another one, made with 1-1/2" headers and (12) 1/2" runners set at 1" centers. I'll again do multiple folds for a stack 36" long, 24" wide, 10" tall. I'll leave room for baffles between each level, but want to try it first without. I would expect better efficiency with baffles, but that makes it harder to keep ash and combustion debris cleaned out.

I understand now why most of the commercially built wood heaters recommend a smokestack temperature above 450* when firing. At lower temps, creosote builds up on the coils, and doesn't get a chance to cook off, at least that is what I'm finding with my proof of concept rig.

My ultimate goal is actually to build a rig I can use for supplemental house heating. I don't want a pressure system (meaning boiler), just an open system with a couple of circulation pumps to inside exchangers. I'm beginning to see why the commercial systems are so expensive.....
 
Current ambient air will be 80F-90F today.
Current water temp 84F.
*Five days use of a bubble wrap type solar cover.
**This pool gets full Sun from 8:00 am - 6:00 pm.
We take cover off when swimming after work. Then pool gets serviced, then cover gets promptly replaced.
 
It's been unseasonably cool here with temps going down into the 40's at night. My pool was 65 this morning.

It's supposed to warm up later in the week to the high 70's, but I don't see the water getting much over 70 anymore. When I have to wear a wetsuit to go in my pool, I guess it's time to take it down. I'll do that this weekend.

It was a good summer.
 

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76 in MD. Autocover on full time. Some lows in the 40's now. Planning to swim a bit this weekend perhaps for the last time. But won't close for a while. Once it's below swimming temp I may have to open the cover at some point so it will cool down sooner to close.
 
Right at 84-85 degrees here, same as all summer, solar panels are doing their job keeping it just right, cooling the water by running at night on hot days, and warming by traditional day time solar on cool days.
 

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