Why Pool and Hot Tub Plumbing Should Remain Separate

Pool and Hot Tub Plumbing

I get asked an awful lot about combining pool and hot tub plumbing kit. In this article I hope to highlight some of the problems you will face if you do try and combine them. I will also highlight some of the areas where it is possible to combine parts.

Pools and Hot Tubs – different roles

What do I mean by pools and hot tubs having different roles. This really comes down to the pool and hot tub plumbing kit that is involved with each and what they should do.

In general, pool plumbing parts are designed for a large volume of slow moving water. On the flip side, hot tub plumbing parts are designed to move a small amount of water quickly.

Pool and Hot Tub Plumbing – The Pump

Firstly the pumps, I have a video on my YouTube Channel here https://youtu.be/x5V8Hz_5APE that explains the difference between swimming pool pumps and hot tub pumps.

In essence, pool pumps are designed to move large amounts of water slowly through a sand filter and then a heater, then return the water to the pool. Hot tub pumps, can have dual roles, but essentially, they are designed to move a smaller body of water quickly through a jet.

The flow rates that you get from a swimming pool pump are generally not high enough to power a 16 jet hot tub for example. You might have a 0.33HP or 0.5HP pool pump. This is a lot smaller than a 3HP dedicated jet pump you would get on a hot tub. It is that size on a hot tub for a reason.

Also, your pool pump might be a “variable speed” pump. This is no good for a hot tub. It will save you money on the running costs on your pool but will not effectively power the jets in your hot tub.

Also, how are you going to control your jets from a swimming pool pump? Where is the control mechanism? The switch? – not going to work.

So, when your pool guy tells you that you can “just add the jets onto the pool pump” he or she is 100% wrong. You cannot just do that at all – it will not work.

The Filter

Hot Tub filters generally are cartridge filters. Pool filters are generally sand filters. This in itself is a big difference. So, why would I not use a sand filter on a hot tub.

Generally speaking, the maximum amount of flow you can get through a sand filter is around 80 GPM. If you think that every jet on your hot tub needs 10 GPM, a 16 jet system needs 160 GPM pretty simple math right.

Correct, however, if you have a sand filter on your system that will only allow 80 GPM max through it, you are never going to be able to power all the jets correctly.

Furthermore, hot tub cartridge filters are designed to have a bypass valve on them. That means if the pressure from the jet pump is too much, it opens to allow the flow through the filter without restriction. They are designed for a purpose and that is to deliver as much flow as possible to your jets.

That said, you could have a separate heating and filtration plumbing system on your hot tub that does incorporate a sand filter. What you can’t do as I have highlighted above is have a sand filter on your jet plumbing – they are too restrictive in terms of flow rates.

What about the Heating?

This is a question that I get regularly. Can I heat my Hot Tub with my pool heater. The answer is generally yes, but you do need to have a separate system to do it or at least some divertor valves to switch the suction and return from your pool to your hot tub.

What this means is that you are going to draw the water from the hot tub, into the pump, divert it into the heater, then return it to the tub. That way, you can heat it. What I don’t suggest you do is try and return it through the jets. You should have a separate hot water inlet system into your hot tub.

Sounds more complicated than it actually is, however, this is totally possible as a setup. If you need some help with this design let me know through the form below.

What about an overflow into my pool?

This is another question that I get asked a lot. There are a few things to think about in terms of the plumbing if you are going to do this.

How are you going to heat the tub? If you are returning pool water into the tub to make it overflow, this is going to have a negative impact on the heating of your tub.

If you are trying to heat the two separately to different temperatures, then this is not going to work well. In short, it will work of course, but the efficiency will be dramatically decreased in terms of heating the tub.

If you are going to have your pool and tub at the same temperature, then sure, this kind of an overflow will work.

The other heating option where this kind of a setup will work is if you are going to use the hot water from the hot tub to increase the temperature of the pool.

The only downside to allowing the hot water from the hot tub to overflow and in turn heat the pool is that you have no real control of the temperature of the pool. You will have a thermostat for the hot tub, but not the pool.

Pool and Hot Tub Plumbing -Pipe Sizes

Depending on the design of your pool, the chances are the pipe sizes will not match with the hot tub equivalent.

What I mean by this is that on a hot tub, the water lines are 2” and the air lines are 2.5”. They are smaller than this on plastic shell tubs, but we are not talking about these in this article.

On your pool, your suction lines might be 2”, but your returns are likely to be 1.5” because there is normally a smaller size pipe on the returns. This means that they would not match up with the hot tub side of things.

Of course, it is totally possible to get the adaptors to drop the size down, but I just wanted to highlight all the potential issues.

Skimmers and Pool Returns

Skimmers and Pool Returns can be used on both hot tubs and pools alike. They are the same parts. However, a hot tub jet is not the same as a pool return.

Hot tub jets allow for the mixing of air and water through a system know as venturi to increase the strength of the jet and also allow bubbles into the tub.

The pool returns tend not to do anymore than look nice and deliver the hot water back into the pool.

In Conclusion

I hope that this article has gone some way to highlighting why hot tub parts and swimming pool parts, in general, should remain separate.

With the right planning, you can combine the plumbing to share a heater for example, but what you cannot do is just “add some hot tub jets” onto your pool pump. This will 100% not work.

If I can help you in any way with your plans and designs, then please do get in touch with the form below.

Happy Hot tubbin’

Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

Thanks - Andi


Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Today, I've helped over 1000 DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi

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