DIY heat exchanger for inground pool.

Aquaman7

Well-known member
Sep 15, 2019
348
NJ
Hello,

I’m researching building a DIY pool heat exchanger. It will be like the one shown in the link below. The outer sleeve will be (1) 10’ - 1 1/2” copper. The inter pipe (where the hot water will go through from the boiler) will be 10.5’ - 1” in diameter. Supply and return will be 1 1/4”. I’m sure I would need to add more 10’ copper sleeves. But I won’t know how many till I do a test run. The boiler is 165btu. Inground pool is 21k gallons. Pump is a Pentair vs pump.
Do you think it will work to heat a 21k in ground pool.

Thank you,
Joe
 

JamesW

TFP Expert
Mar 2, 2011
23,199
A 165,000 btu/hr heater with an efficiency of 100% transfers 165,000 btu per hour to the water.

At a minimum required flow of 20 gpm, there will be 2,400 gallons of water (10,000 lbs.) that receives the heat.

Each btu raises the temperature of one pound of water by one degree Fahrenheit.

165,000 btu into 10,000 pounds of water is 16.5 degrees of temperature rise (165,000/10,000).

So, the maximum temperature rise you should ever have is 16.5 degrees Fahrenheit.

Higher flow results in a lower temperature rise.

40 gpm = 8.25 degrees temperature rise.

20,000 gallons is about 166,800 lbs of water.

The expected temperature rise per hour should be about 1 degree per hour assuming a 100% efficiency not accounting for heat lost from the pool, which will vary depending on the weather and if the pool is covered or not.

Do you have an estimate of the expected efficiency of the heater?
 

Aquaman7

Well-known member
Sep 15, 2019
348
NJ
A 165,000 btu/hr heater with an efficiency of 100% transfers 165,000 btu per hour to the water.

At a minimum required flow of 20 gpm, there will be 2,400 gallons of water (10,000 lbs.) that receives the heat.

Each btu raises the temperature of one pound of water by one degree Fahrenheit.

165,000 btu into 10,000 pounds of water is 16.5 degrees of temperature rise (165,000/10,000).

So, the maximum temperature rise you should ever have is 16.5 degrees Fahrenheit.

Higher flow results in a lower temperature rise.

40 gpm = 8.25 degrees temperature rise.

20,000 gallons is about 166,800 lbs of water.

The expected temperature rise per hour should be about 1 degree per hour assuming a 100% efficiency not accounting for heat lost from the pool, which will vary depending on the weather and if the pool is covered or not.

Do you have an estimate of the expected efficiency of the heater?
Thank you for your York.. The efficiency of the boiler is 80%
 
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NJpoolNoob

Member
Dec 27, 2020
16
Hammonton NJ
Your basically building a side arm heat exchanger. Those work well for transferring heat to a water heater or spa but a pool would be a little much. If your handy and looking to diy. The wood boiler guys use old propane tanks. They cut them open and insert a coil of soft copper into it attached to 2 outlets welded to the tank. Then weld the tank back together and insulate it. BTW if you go this route make sure to put a good pressure relief on it. Definitely dont want more then a few psi in the tank.
 

Aquaman7

Well-known member
Sep 15, 2019
348
NJ
Your basically building a side arm heat exchanger. Those work well for transferring heat to a water heater or spa but a pool would be a little much. If your handy and looking to diy. The wood boiler guys use old propane tanks. They cut them open and insert a coil of soft copper into it attached to 2 outlets welded to the tank. Then weld the tank back together and insulate it. BTW if you go this route make sure to put a good pressure relief on it. Definitely dont want more then a few psi in the tank.
Yea. You might be right. And the pool is 21k.
 

NJpoolNoob

Member
Dec 27, 2020
16
Hammonton NJ
I was actually looking into doing something similar. No NG here so my options are propane, heat pump, or solar. So I had considered putting a wood boiler in my pool house and using a large heat exchanger to heat the pool. I have an abundance of wood but the cost of the project is just too much. In the end I think I'm going to install a 7kw solar kit on the pool house and get the largest heat pump I can find.
 
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