Spa Venturi fittings and sizing

[Tbarns]

Hey all, I am building a pool and we have a spa with a dedicated pump/therapy jet system.

The lines are sized at 2-1/2” on the drawings and I had a couple of questions:

1) I have been looking online and I’m looking for a gunnite fitting that has 2-1/2” water inlet and 2-1/2 for the jet (I assume that’s what I need) can anyone point me to a site that carry's these?

2) What size should the air line be? (This is not in the plans, but I’d like to add it.)

3) kind of generic for both the pool and spa pumps, but both pumps have 2” unions for the plumbing, is it as simple as just immediately upsizing to 2-1/2” right out of the pumps? And on the other end at the therapy jets where I’m running 2-1/2”, can I just reduce to 2” at the jet body if I can only find 2” and still maintain the flow advantage of the 2-1/2”? I’ve seen 2-1/2” at the jet with 2” water and 1-1/2” air. Or does that defeat the purpose of running 2-1/2” from the equipment to the spa?

 

[setsailsoon]

T,

Welcome aboard. I am completing an OB pool right now and had all the same questions you do about the spa a few months ago. There are standard in-wall fittings made by a couple companies and the ones I have are made by Hayward. I think they all have the same sized piping that connects the jets in the spa wall. Here's a great video that shows how they work. Subscribe to the channel an you'll find a LOT of very helpful videos about all kinds of other spa features. You end up with one of these fittings inside the gunite wall for each jet. Then there's a 2 1/2" pipe that brings the air, water mix out through the jet. There are several brands of jets that you can get but they all seem to require their own jet housing. Now's a great time to decide which way you want to go. I spent hours looking at all the choices. At the end I used the Hayward because they have several types of simple pointable pressure heads and a pretty nice therapy jet. I was also more comfortable that their jets would be available long term since they're a major pool brand. Waterway also makes a great system and they're likely to be around a long time since they've been supplying pool equipment for a long time also. Standard jets are pretty cheap (under $15) but the therapy jets can be up to $50. Also, in my case there's a really handy tool for the Hayward jets to install and remove them... If you go Hayward, I'd get the tool it makes life a lot easier.

I ran 2 1/2" pipe for the air and water to reduce pressure drop since my lines are about 100' long. Most of the articles and technical data seem to indicate you should plan for 10 gpm per jet. Piping pressure drop depends on how many jets you'll be running. An easy way to check line size is just to make sure the total flow keeps you less than 7 ft/sec. For 2" pipe I was over 10 ft/sec. so I went up to 2 1/2". Here's a handy nomograph to check your velocity. Get one of the newer silencer brand air pumps. They're amazingly quiet and very easy to install. Make sure you order the right voltage, they're not interchangeable and I liked 240 vac since it's over 1 hp to reduce wiring size.

Here some further reading from our Wiki about spas that may be useful.

I hope this helps.

Chris

 

[Tbarns]

Thanks Chris, in regards to the pipe sizing, I am running 2-1/2” as well. I’m not seeing jet bodies that have fittings for 2-1/2” though.

My question is if I run 2-1/2” lines to the spa, then the loop around the spa is reduced to, for the water pipe, 2”, am I still benefiting from the 2-1/2” lines back to the pipe, or am I wasting my time by choking it down at the jet?

 

[setsailsoon]

Thanks Chris, in regards to the pipe sizing, I am running 2-1/2” as well. I’m not seeing jet bodies that have fittings for 2-1/2” though.

My question is if I run 2-1/2” lines to the spa, then the loop around the spa is reduced to, for the water pipe, 2”, am I still benefiting from the 2-1/2” lines back to the pipe, or am I wasting my time by choking it down at the jet?

No, choking down at the end doesn't mean you get no benefit from the pipe size back to the pad. What you want is to get plenty of water to the jets. Every foot of pipe has some friction loss from the water "rubbing" on the pipe. So if you have a long run of pipe you can get more loss through the pipe before it gets to the spa. This is made up by the pump. The more loss the higher the pressure required at the pump. Pool pumps flow less water at higher pressures. The relatively short run of pipe around the spa doesn't have that much drop usually but the run to the spa can be over 100'. Normally the designer will check hydraulics to size the pipe. Normal flow rates don't have a lot of pressure drop per 100' but that can go up a LOT if you have too high of flow. A guide they use is to avoid long runs of pipe with velocity over 7 ft/sec. This is easy to check. Just multiply the number of jets time 10. This gives your required flow rate. Then look at the velocity you get to see if you're above normal and let this help you decide. Take my case I have 10 jets that need 100 gpm. If I used 2" this is well over 10 ft/sec. So I went up to 21/2". This is a pretty simplistic way to do it and you should do a complete hydraulic analysis. Many building departments require it and it's really the best way to size your pump. We have experts here that can do some very fancy analysis. My system is much different than your standard pool and their analysis was very helpful for me. I upgraded the pump on their analysis and I'm very happy with the results. How many jets do you have? @mas985 @JamesW ... over to you guys.

Chris

 

[Tbarns]

My pool designer did call for 2-1/2” based on the hydraulic calcs.

My equipment pad is roughly 55-60’ from the spa and this is a dedicated pump for the spa recirculation jets. I planned to run 2-1/2” as designed, but didn’t know if I was in for an issue with only finding the 2” jet bodies.

 

[mas985]

Hey all, I am building a pool and we have a spa with a dedicated pump/therapy jet system.

How many jets and what is the jet nozzle orifice size?

The lines are sized at 2-1/2” on the drawings and I had a couple of questions:

1) I have been looking online and I’m looking for a gunnite fitting that has 2-1/2” water inlet and 2-1/2 for the jet (I assume that’s what I need) can anyone point me to a site that carry's these?

That is not what you need. The loop around the spa can be 2 1/2" pipe and bushings are used at each tee to downsize to the venturi tee being used. That is what is normally done. Remember that each venturi carries only a fraction of the total flow.

2) What size should the air line be? (This is not in the plans, but I’d like to add it.)

I would use at least 2 1/2" air line and make sure it has a Hartford loop near the spa so you can avoid using a blower. When air lines fill up with water and it is deeper than a few feet relative to the water level, the venturis on their own will have trouble removing the water from the air line.

3) kind of generic for both the pool and spa pumps, but both pumps have 2” unions for the plumbing, is it as simple as just immediately upsizing to 2-1/2” right out of the pumps?

Yes with bushings. However, most large pumps used for spa jets will also accept 2 1/2" plumbing fittings on the outside of the union. What is the pump make/model?

And on the other end at the therapy jets where I’m running 2-1/2”, can I just reduce to 2” at the jet body if I can only find 2” and still maintain the flow advantage of the 2-1/2”?

Yes, that is the way it is normally done.

I’ve seen 2-1/2” at the jet with 2” water and 1-1/2” air. Or does that defeat the purpose of running 2-1/2” from the equipment to the spa?

No it does not defeat the purpose of 2 1/2". Head loss is related to both pipe diameter AND the pipe length at that diameter. So very short runs of smaller pipe are not really an issue. Plus as I mentioned earlier, each jet will carry only a fraction of the flow rate so it is really no issue at all.

 

[setsailsoon]

My pool designer did call for 2-1/2” based on the hydraulic calcs.

My equipment pad is roughly 55-60’ from the spa and this is a dedicated pump for the spa recirculation jets. I planned to run 2-1/2” as designed, but didn’t know if I was in for an issue with only finding the 2” jet bodies.

T,

Take a look at the reply from Mark and please answer his questions... now that I think about it my piping around the spa was exactly the what Mark describes. Even if you have a design would be good to see what Mark comes up with as an independent check. He and James found a couple things in my designer's calcs that weren't correct and even though the building department approved I implemented and got a better performing pool. They both really are experts.

Chris

 

[Tbarns]

Sorry guys, crazy couple of weeks. Thanks for the responses.

How many jets and what is the jet nozzle orifice size?

6 jets, I’m not sure if the orifice size off the top of my head.

That is not what you need. The loop around the spa can be 2 1/2" pipe and bushings are used at each tee to downsize to the venturi tee being used. That is what is normally done. Remember that each venturi carries only a fraction of the total flow.

That’s what I ended up doing, thanks

I would use at least 2 1/2" air line and make sure it has a Hartford loop near the spa so you can avoid using a blower. When air lines fill up with water and it is deeper than a few feet relative to the water level, the venturis on their own will have trouble removing the water from the air line.

I did this too, thanks. The Hartford loop is about 5’ from the spa wall

Yes with bushings. However, most large pumps used for spa jets will also accept 2 1/2" plumbing fittings on the outside of the union. What is the pump make/model?

The therapy pump dedicated to the spa is the CircuPool SmartFlo Variable Speed 1.7 THP

Yes, that is the way it is normally done.


No it does not defeat the purpose of 2 1/2". Head loss is related to both pipe diameter AND the pipe length at that diameter. So very short runs of smaller pipe are not really an issue. Plus as I mentioned earlier, each jet will carry only a fraction of the flow rate so it is really no issue at all.

Running with the 2-1/2”.

Thanks for the help here. I’m not super against the blower if needed. I was in a few pools this weekend visiting friends and was checking out their equipment and how they ran. They both had blowers and they weren’t as loud as I thought it would be and my equipment is around the corner of the house. Though I would like to keep it with the Venturi alone.