# Thread: How do I calculate time and propane required.

1. ## How do I calculate time and propane required.

I believe my pool is about 35,000 gal. Initially the online pool calculator said I had 38,000, but I figure with the flat shallow end and the angles of the deep end its about 35K. At lease when I use pool math my changes in FC are closer to what it says they should be using the 35K value. I have a Master Temp 400K LP heater. How do I calculate how long it will take and how much LP it will burn for each degree in temp increase? Also, my CYA is 30. I have an automatic cover so the pool is covered unless we are using it. Is 30 alright or should I raise it?

2. ## Re: How do I calculate time and propane required.

That's a great question. Tagging along for the ride on this thread.

3. ## Re: How do I calculate time and propane required.

One BTU of heat input will increase the temperature of 1 lb of water by 1 degree F. So your 35,000 gallon pool has 8.4 lbs per gallon of water or 294,000 lbs of water in it. Your heater is rated as 400,000 BTU/hr. So it will take 0.735 hours or 44mins to raise your water temperature 1 degree F. You have to figure your heater is only at best 90% efficient (you can typically look up efficiency ratings on heaters on the EnergyStar website). 1 degree F per hour is not an unreasonable heating rate.

Also, your pool is not perfectly insulated so that drops the heating efficiency further. Keeping the pool covered while heating holds the heat in a lot better than trying to heat an open pool as 1 gallon of water evaporated from a pool carries away over 8,000 BTUs of heat. So, if your pool water is a lot hotter than the ambient air temperature and the relative humidity is low enough, you lose more heat to evaporation than you can deliver through gas heating.

See this website for a good starter on pool heating - Gas Swimming Pool Heaters | Department of Energy

5. ## Re: How do I calculate time and propane required.

In practice, you will never nail a metric.
Wind, "line loss" & ambient temp play a huge role.

6. ## Re: How do I calculate time and propane required.

Also at the in terms of LP consumption 1 gal of propane has 91k Btu. So your 400k btu heater use about 3.5 gal per hour of run time.

7. ## Re: How do I calculate time and propane required.

Good info. That will give me an idea so I can roughly figure cost if we want to heat it up for a weekend.

8. ## Re: How do I calculate time and propane required.

1 BTU will heat 1 lb of water 1 degree in 1 hour. Not accounting for loss, so add 10-20%

35,000x8.33 = 291,550 lbs

It will take 300,000 BTU to increase your pool temp 1 degree in an hour.

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