# Thread: Use tankless natural gas heater to heat the pool?

1. ## Use tankless natural gas heater to heat the pool?

So anyone tried to use tankless natural gas heater to heat the pool? I have Navien 240-A for domestic hot water, it is rated for 200,000 BTU. So theoretically it can easily raise the water temperature overnight by 8F (when nobody at home is using hot water). What do you think?

2. ## Re: heating pool with Home Depot electric water heater?

Originally Posted by Den
So anyone tried to use tankless natural gas heater to heat the pool? I have Navien 240-A for domestic hot water, it is rated for 200,000 BTU. So theoretically it can easily raise the water temperature overnight by 8F (when nobody at home is using hot water). What do you think?
How big is your pool ?
Where are you located ?

Gas pool heaters are rated by Btu (British thermal unit) output. Outputs range from 75,000 Btu to 450,000 Btu.
Calculating Approximate Size

To calculate an approximate heater size for an outdoor swimming pool, follow these steps:

Determine your desired swimming pool temperature.

Determine the average temperature for the coldest month of pool use.

Subtract the average temperature for the coldest month from the desired pool temperature. This will give you the temperature rise needed.

Calculate the pool surface area in square feet.

Use the following formula to determine the Btu/hour output requirement of the heater:
Pool area multiplied by temperature rise multiplied by 12.
One problem I think with a water heater is they are not built the same as a pool heater
A water heater is made to run for a while...then shut off.....infrequent use
A pool heater is most likely a lot more heavy duty, they are made to run for hours at a time if not days

3. ## Re: Use tankless natural gas heater to heat the pool?

This is regular pool 16x32.
I am located in Kelowna, BC, Canada. Pretty hot here in July-August (not much need to heat the pool those months), but I hope to use the pool for 2 more months before and after.
What could possibly go wrong if the heater is used constantly? It can do 11GPM with 25F temperature rise. 200,000 BTU/hr

4. ## Re: Use tankless natural gas heater to heat the pool?

I just do not think they are designed to be running hours at a time ... may end up melting the unit or something.

I still do not know your pool size .. is that 16' x 32' x ? depth or is the 16' diameter by 32" deep? IN ground / above ground? Add all your pool and equipment details to your signature.

5. ## Re: Use tankless natural gas heater to heat the pool?

Another perspective:

EDIT: I don't know if there are copper parts in the flow but if there are that may be a problem.

6. ## Re: Use tankless natural gas heater to heat the pool?

Sorry, guys. It's inground 16'x32' pool with 9' deep end. I estimate about 20,000 gal in size.

7. ## Re: Use tankless natural gas heater to heat the pool?

Assuming 85% efficiency the heater puts out 170kBTU/hr
You pool is 20k gallons * 8.33 lbs = 166,600 pounds of water
Assume you run it for 6 hours you can supply 1,020,000 BTU overnight.
Divide by the weight = 6 degree temp rise.

I have no idea what the efficiency of these are ... likely less than 85% since you are moving less water through than a pool heater would be capable of doing. Higher delta temperatures are lower efficiency I think.

You must use a pool cover or you will be loosing a lot of that heat to evaporation in the cool night air.

8. ## Re: Use tankless natural gas heater to heat the pool?

Yes, numbers work ok. I do have solar cover. My worry is if water heater will be able to handle such load and if anyone has experience with that.

9. ## Re: Use tankless natural gas heater to heat the pool?

It sounds like you want to use your tankless hot water heater that you use for your house hot water and when not in use use it to heat your pool.
Is that correct?

If it is, then just the connection of your pool to that system would be a code violation, as you are connecting non potable water source to potable one.
That heater is meant to handle a certain flow rate which you would have to meet for it to work properly, I would think it would be pretty low 5 to 10 gallons a minute. Also it is used to higher pressure, and pool pressure would be quite a bit lower, not sure how that would effect the use. Pool heaters have special heat exchangers to handle the harsh conditions of a pool. Most are Cupro-Nickel.
In general sounds like a bad idea.

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