Help dispelling the Bigger Is Better myth for pool pumps


LifeTime Supporter
Aug 16, 2007
Ottawa, Canada
I'm building a small 7000 gallons inground pool with no spa or water features. I've already had a lot of trouble convincing the pool builder to substitute the "included" 1.5HP for a lower HP pump. I wanted 3/4hp, but finally settled for a 1HP pump. The seller gave me the weird look and commented that this was the first time that somebody asked for a smaller pump and that it didn't make much sense to him.

The pool delivery guy also looked at me like I was a freak for requesting a smaller pump and so did some of the installers.

I've explained them that I was only wasting electricity with the bigger pump and that filtering a such a small pool with such a big pump was like trying to drive a nail through drywall with a sledgehammer.

I'm also concerned about excessive pressure the pump would cause in the small 1 1/2" inch pipes used to plumb the pool and in my solar panels.

Is there any good documentation available on the web to support the importance of proper sizing of the pump for the pool?


Mod Squad
LifeTime Supporter
Platinum Supporter
TFP Expert
In The Industry
Apr 1, 2007
Sebring, Florida
Perhaps not much documentation that's not fragmented, but I can give you an overview of why smaller is better.

First of all, 7000 gal. should turn over 2-3 times in a 24 hour period. That's a generally accepted rule of thumb. So, you need to pump about 20k of water / 24 / 60 min. = only 14 gal / theory, that's all you need.

The pump that was delivered to you probably does somewhere around 40-50 gpm. That's not a problem so far unless your filter (that's where they usually skimp) is not rated for at least that much and, ideally, 25% more or so. Pushing that much water thru a skimpy filter causes unneccessary resistance (higher psi) and, in some cases, can actually blow dirt back into the pool.

Add on to this the higher electrical costs and it soon adds up that a large pump is a waste of money and actually detrimental to your system. If your PB doesn't understand that, he hasn't done his homework.

A 1/2 to 3/4 pump sounds like it would fit your system much better


LifeTime Supporter
TFP Expert
May 28, 2007
Middle Tennessee
I'm with Dave, your pb hasn't done his homework. He's subscribing to the "maximum flow is best", and someone, somewhere told him that a 1.5hp pump works best with the filter you're getting. He'll probably also tell you to leave your pump run for 24 hours/day too, to get maximum circulation and water turnover which, as Dave pointed out, isn't needed.

I would ask them why they think you need a 1.5 hp pump for your pool with no water features, and see what they say.

FWIW, I blindly followed what they said for the first two years that we had the pool. I finally wised up this year and started doing some research on the 'net (mainly about running the pump 24/7), and found out that I was just wasting electricity, basically. I am a lemming no more. :)


LifeTime Supporter
Aug 16, 2007
Ottawa, Canada
They don't really have an answer to my question about why they think that the 1.5 HP pump is needed for my pool. They told me that they install this pump with all the pools that they sell, it's part of the "standard kit". Deviating from the standard kit seems to be unusual for them.

I was in discussion with another pool builder before I bought the pool and It was the exact same story... The seller told me proudly: with that pump you could filter a 20x50 pool!

There are not that many PB in my area and the one I picked has the best reputation with the BBB and has been in business for 35 years. To be fair, this pump sizing annoyance is the only issue I had with them so far. The actual installer seems to be very knowledgeable, listens well and is very accomodating with my demands for the construction so far.


LifeTime Supporter
TFP Expert
May 3, 2007
Pleasanton, CA
I cover a bit on pump sizing here but the basic rule of thumb is to size the pump for the maximum flow required for the pool. If you have only a pool without a spa, water feature and/or cleaner (vacuum or pressure), then you can usually go with the smallest pump possible. High HP pumps mean faster turnover but not necessarily a cleaner pool. More than 3 turnovers per day is waste of energy.

The best thing to do is ask the PB why such a big pump? If that doesn't work then ask him to pay the power bill for the first year. Seems as though most PBs couldn't care less about energy efficiency.

A 1 HP pump can push a lot of water. Mine runs at about 88 GPM. Your 1 1/2" plumbing will have much higher head loss so the flow rates will drop a bit. In the link I gave, I compare several HP pumps with several examples of plumbing system. Yours is likely to be closer to plumbing scenario A & B depending on how the plumbing is configured. You are likely to be somewhere in the 50-60 GPM range but without more details on your plumbing, it is hard to say.
i can conform that a 1.5 will filter a 20X50, heck it does my 25X50 quite well, at only 40gpm though, so i run 24/7, and only turn over about once aday but my water has never been foggy or alge infested, it would be better if they didnt have the pump 115 ft away from the closest return if i did my math right, but i have always been told BIG filter small pump is the best case for a pool.