Pump Size

[thepoolman1]

Unless you will have 2.5" plumbing or larger, a 1.5hp pump will be too large for your system. You will also need a filter that can handle the flow of a pump that large. If you are going to use a 2-speed pump (highly recommended), the occasional use of the high speed of a 1.5hp would probably not cause many problems, even on 2" plumbing.

I have successfully filtered older pools in the 40 - 50k gallon range that had very undersize (for today's standards) plumbing, hand-formed skimmers and usually only 1 return line and inlet with 1/2 and 3/4hp pumps. Bigger is seldom better in pool pump sizing.

[stualden]

Poolman1, is a 1.5 horse dual-speed likely to be a good candidate for a 32,000 gal. in-ground pool too?

I have two motors, both of which are on their deathbeds. One is a 1 horse, one is a 2 horse (but with an impeller that says 1.5 horse). Pumps are old UltraFlow, installed by Sylvan in 1991. All plumbing is 1.5", except (curiously) for the final return to the spa, which is 2". The pool filtration circuit passes through a Titan stainless steel 60 sf filter and a new Sta-Rite heater.

I had always assumed that the 2 horse was for the pool, but your note suggests that it's for the spa jets. Does that sound right? Everything was unassembled when I bought the house and I didn't know any better.

Is the two-speed a good choice for the pool, with a manual switch just to get high speed when backwashing or doing other maintenance chores? Thanks.

[duraleigh]

Poolpup,

Poolman's advice is on the money. I have a full-rated 1.5HP pump for a 43,000 gal. pool (2" plumbing) and I would've been a little more efficient with a full rated 1HP. My only saving grace is I have a very large sand filter (950 lbs) so my system is ok.....just could've saved some money with less pump and had a little better system.

(Full-rated pumps are about .5HP stonger than up-rated pumps)

Stu,

based on your preliminary info, 1.5 sounds a little large for the pool....unless your going to drive both pool and spa from one pump.....then maybe a 2hp 2-speed would be a good mix. Others more experienced with spas than me will chime in soon and give you a better-educated answer.

[stualden]

Thanks Dave. I'll always use a separate pump for the spa jets, so the existing 2 horse (or a direct replacement) should be okay for the spa. I read something relating hp requirements to number of jets - in this case I have 6 (it's a nice roomy spa).

I will get out the pencil and paper and the Ultra Flow charts and figure out what my requirements are for the main filter circuit. I suspect that 1 hp single speed is right (i.e., Sylvan sized it correctly). What I want to figure out is if the Ultra Flow pump can work with the lower RPM of a two-speed motor, and if so, what size motor will give best results for regular filtration at the lower speed.

[msm859]

Although the number of jets you have in your spa is relevant, it is probably more important what size pipe they used. My guess is a 2hp pump is TOO BIG. There are tables that will tell you how much flow you can run through different sized pipe.

[waterbear]

Spa jets require a more powerful pump in a shared pool/spa system. This also requires an oversized filter to match the pump. This is how my 6600 gal pool ended up with a 150 sq. ft. cartridge filter and 1.5 uprated whishperflo pump...defininately overkill for the pool but needed to run the spa! I am actually very happy with it...my pool stays crystal clear and I could probably run the filter for a year before the pressure rises enought to warrent cleaning (although I do clean the cart montly). I looked into a 2 speed pump but there was some concern as to whether I would actually have to go with a larger pump HP to be able to achieve adequite circulation on low speed with my setup when it was being designed.

[stualden]

Thanks everyone. I will check on sizing for the spa pump too.

In my case, the spa pump is on a separate circuit that is completely independent of the filtration circuit. In other words, the spa has two drain holes for filtration (which I normally don't use - only for draining the spa), two returns for filtration (which I do use, causing a waterfall into the pool), two drain holes for the spa circuit, and six spa jet returns. There is also an air blower in the spa circuit.

So in my case, I guess the spa pump sizing is primarily a function of how hard I want the jets to feel? The spa circuit is all 1.5" pipe.

If my pump curves (UltraFlow pre-94) don't show results for the low speed of a two-speed pump, does that imply that it won't work (or at least not well), or just that two-speed motors weren't common back then (1991)?