Pool heater sizing

[Highlandreef]

Hi folks,
Wanted to ask what everyone thought about properly sizing a pool heater for our pool.
Our pool is 18x33 and is 54" tall
What btu heater should I be looking at?
Pool store said to buy a 200k btu heater but I was wondering if that's enuf to heat the pool up a little due to the cool nights we sometimes have in Indiana and would also like to try and extend the pool season.
I don't want to buy something and it be too small and have to run the thing 24x7, you get the idea

 

[mas985]

A larger heater will heat the pool faster than a smaller heater (2:1 for 200k vs 400k). So it will depend on how you plan to use the heater. If you want to shut it off for most of the week and only heat the pool on the weakends, then I would go with the larger heater so it can heat up quicker. Also, I wouldn't think of heating a pool without a cover or you will be just wasting your money.

Just a few numbers: A 200k heater will raise the temperature of a 15k pool 1.25 degrees/hour while a 400k is 2.5 degrees/hour (assumes 78% efficiency).

 

[Highlandreef]

We are mostly wanting to run the heater for a warm up during the weekend or weekday afternoon.
So sounds like a 400k btu would be a good fit. I definitely don't want to run the heater like 16 hours to bring it up 15 degree's
We do have a cover.
Thanks for the reply.