Oversize? SWG, Filter, Heater


May 2, 2020
Raleigh, NC
I read a lot of posts about over-sizing the SWG and filter when building a pool. We are about to get started and will be building a 21,000 gallon pool and i want to better understand what is considered oversized appropriately and what would be considered over kill. Our builder is showing a 40,000 gallon rated SWG and a filter that is rated at about 100 gpm. He said we could upgrade to 60,000 gallon rated SWG and 140 gpm filter, but i wasn't sure if they had already recommended the appropriate oversized equipment or we should think about the increasing capacity of the equipment?

They also have a 400,000 btu heater listed currently.

This pool will have a swimming lane included and will be used everyday year-round except maybe 4-8 weeks during the coldest part of the winter.

I want to make maintenance easy and normally always go big. But i am not sure what big is and where that ridiculous line is.

Thanks for any help!
Last edited:


Well-known member
Jun 16, 2019
For 21k gallons you don’t *need* the max size of everything. 2/3 would be plenty. For example, a 40k SWG and a 350 sq ft cartridge filter. Going bigger however will cost you peanuts compared to your build. The SWG upgrade is around $150 for most product lines and filters would be around $200. Both would have extended life from being used less therefore recovering the upgrade cost and then some.

Plus, even less maintenance on the filters.


Gold Supporter
Feb 23, 2020
St Simons Island GA
We have about 20,000 gallon pool with a SWG for 40, 4 cartridge filter, and 400k btu heater. SWG typically runs between 15-20% to maintain chlorine around 5. (I run pump 24 hours mostly at low speed). Have only cleaned cartridges twice since build last September and that was only cause I thought I should. Pressure didn’t change.

It’s a little warmer here in winter but heater raised pool temperature from around 65 to 80 in February in about 6 hours. Also was expecting a large gas bill, but was surprised at the $40 bill including water heaters and stove for the month.


Well-known member
Mar 4, 2015
Sugar Land , TX
I have 8500 gallon pool with a Pentair 550(?) cartridge filter. I clean it 4 times per year because of all the tree's and pollen. My PB said to over size everything since it did not cost that much more. Heater is 400btu Pentair, heats out spa up quickly :)