Spa pump horsepower

Drew80

Well-known member
Feb 26, 2013
146
Austin, TX
#1
I have a 1,250 gallon spa with 8 jets, and I have a single speed 2HP pump that powers both it and my pool. The 3 jets in the pool are really strong, but the pump isn't strong enough for the 8 jets in the spa. The jet inserts barely spin and the water doesn't ripple at all.

What HP pump would I need to get those things really moving?
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,293
Pleasanton, CA
#2
It depends on the flow rate requirement of the jets. Standard 15 GPM jets require a total of a 120 GPM which is very hard to get no matter what size pump you put on the plumbing unless you have very large pipe and don't go through the pad equipment.

What size pipe did they use going to and from the spa?

Is there a separate jet pump or does the water going to the jets also go through the filter?

Do you know the flow rate requirement of the jets or the nozzle size of the jet?
 

mas985

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LifeTime Supporter
May 3, 2007
12,293
Pleasanton, CA
#4
What is the filter pressure?

Is the 2 HP pump a full rated or up rated version? What is the model number?

Unfortunately 2" pipe is really much too small for a spa.
 

DangerBoy

Well-known member
Oct 4, 2018
54
Calgary/Alberta
#5
What is the filter pressure?

Is the 2 HP pump a full rated or up rated version? What is the model number?

Unfortunately 2" pipe is really much too small for a spa.
I disagree in some cases. My '95 Hot Spring Grandee has a 1 hp jet pump and a new replacement 1.5 hp pump on 1.5" lines each powering about 6 jets each. That's not very many jets but I get reasonable flow and pressure out of them despite the small line size and low horsepower. My system works okay because there are so few jets and each jet pump gets 2 filters each so you don't have any constriction on the intake/suction side. Up the number of jets significantly then you'll need a much higher discharge rate from the pump to compensate so more hp and bigger diameter lines would be needed there.

In this case, the OP has a 2 hp pump on 2 inch lines and only 8 jets so I would think he should be able to get enough throughput on that system to make the jets work okay unless they really underdesigned that system.

The first thing I would do is do a quick test running the jet pump with the filter off just to see if the filter is where the restriction is. If throughput increases significantly with the filter off then either clean or replace the filter.

If the filter is not the issue then what other things could cause the system to perform poorly? Let's think this through. (Note: I am thinking here as if it's a standalone portable spa so some of the things I've listed may be N/A for your setup.)

1. Restrictions in the pump suction and/or discharge lines either due to an obstruction or the lines being undersized (personally, I don't think they are for only 8 jets but it depends a lot on how long they are)
2. Pump impeller worn out
3. Pump impeller undersized (e.g. having a 1 hp impeller on a 2 hp motor)
4. Pump motor being underpowered (design issue)
5. Pump motor being weak from age and wear
6. A leak in the suction and/or discharge lines
7. Too much pressure drop through the system due to the suction and discharge lines being too long and narrow for the pump size. (I doubt this is it given it's a small sized tub and has 2" lines in and out of the pump. My tub is much larger and therefore the lines running to the jets are much longer and I have less hp and both the inlet and outlet lines from the pump are only 1.5".)
8. Not enough current getting to the pump? (e.g. being wired for 240V but only getting 120? Is that possible? Corroded/oxidized wire connections in the GFCI box or at the pump possibly?
9. Pump motor not turning enough rpms (e.g. it's a 2 speed motor only wired to run at the lower speed or the motor is a 1730 rpm one speed motor and is supposed to be a 3450 rpm motor.)

That's about all I can think of. Out of all of the above, I would guess the most likely cause is the filter but fortunately, that's the easiest thing to test. How much do you know about the wet end and motor that's in there? Are they original to the tub? If you bought this tub second hand it's possible a previous owner replaced the motor or wet end or both with something that's incorrect like an undersized wet end or a motor with the wrong specs or got a motor that should work but wired it incorrectly so it's not putting out what it's capable of.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,293
Pleasanton, CA
#6
I disagree in some cases. My '95 Hot Spring Grandee has a 1 hp jet pump and a new replacement 1.5 hp pump on 1.5" lines each powering about 6 jets each. That's not very many jets but I get reasonable flow and pressure out of them despite the small line size and low horsepower. My system works okay because there are so few jets and each jet pump gets 2 filters each so you don't have any constriction on the intake/suction side. Up the number of jets significantly then you'll need a much higher discharge rate from the pump to compensate so more hp and bigger diameter lines would be needed there.
That is a stand alone spa and pipe runs are generally very short and use multiple runs. My comment was for in-ground spas that have very long runs between the pump and spa. Please don't confuse the OP.

In this case, the OP has a 2 hp pump on 2 inch lines and only 8 jets so I would think he should be able to get enough throughput on that system to make the jets work okay unless they really underdesigned that system.
80 GPM on 2" pipe is 8 ft/sec velocity which makes it well above recommendations especially for entrapment.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,293
Pleasanton, CA
#8
You are quoting a pool store? Really?

You can't always believe what you read on the internet. You can run at 85 GPM through 2" pipe if you really want to but there are several issues with that. First, for a spa and suction side plumbing in general, VGBA regulations that most states now follow dictate a maximum of 6 ft/sec velocity which is about 60 GPM in 2" plumbing. This reduces the risk of entrapment. Second, running over 8ft/sec greatly increases head loss significantly limiting how much flow rate a pump can produce.

Again you can run above 6 ft/sec if you so desire. It just is not advisable and I wouldn't say it is OK!

http://www.wvdhhr.org/phs/pools/Virginia%20Graeme%20Baker%20Act/ANSI-APSP-7%202006%20suction%20entrapment%20PDF%20with%20covers.pdf
 
OP
OP
Drew80

Drew80

Well-known member
Feb 26, 2013
146
Austin, TX
#9
So the mistake was that my pool builder chose to run 2" PVC to 8 jets, and it doesn't seem like there's any good way to fix that short of replumbing (which I'm not going to do). Can I just cap 4 of them to increase pressure on the others?
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,293
Pleasanton, CA
#10
Yes, that is probably your best bet. But I would just try caping two of the jets. That might be enough.

But what is the filter pressure now?
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,293
Pleasanton, CA
#12
You really shouldn't allow the filter pressure to climb more than about 25% or 5 PSI. That could be part of the issue with the jets as it is reducing the flow rate significantly.

I can estimate the flow rate for you and how it would change with different pumps and/or changing the number of jets as well as cleaning the filter but I need a bit more information:

Distance from pool to spa?

Height of the pump relative to the spa water?

Is there a single run for the suction and the return for all 8 jets or are there multiple runs on both the return and suction side?
 
OP
OP
Drew80

Drew80

Well-known member
Feb 26, 2013
146
Austin, TX
#13
I'm sure the pressure doesn't help, but the jets are weak even when the filter is completely clean. As we've determined, there are just too many of them

About 25' from the equipment to the pool returns. The spa is a spillover on the other side of the pool - that run is about 40'

The ground is flat between the spa and the pump, so the rise is only about 1' from the top of the water to the intake pipe of the pump

Single runs entering and leaving the valves. The spa has 2 drains and 8 jets, but those splits happen before/after
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,293
Pleasanton, CA
#14
At 30 PSI, the pump should be producing less than 60 GPM to the jets which is too little. However, if the filter is clean with a filter pressure of 20 PSI and assuming the skimmers and pump basket are also clean, then the pump should be producing over 90 GPM which should be more than enough flow rate for 10 GPM jets.

Are there any valves which bypass flow rate around the jets?

I would clean the filter & pump basket and get another filter pressure measurement to confirm.