Thread: Hot Tub Heat?

1. Hot Tub Heat?

I really have no clue where to put this, but Everything Else seems like a good place.

How much heat does a spa hold if it's at 102-104*F? My spa is connected to the pool and I'm wondering if I empty all the hot water into the spa into the pool how many degrees the pool will rise? The pool is aprox. 4000 gallons and the spa is about 350. If you need any other info, just ask.

Thanks,

2. Re: Hot Tub Heat?

My SWAG would be:

350 / 4000 = @ 13 so 1/13 of the difference in temperatures.

Spa temp 103 Pool .. Wisconsin ... February ...33 hopefully.

103 - 33 = 70 temperature difference

so 70 /13 = 5.38 degrees before the outdoor temperature starts to drop it ( 3 seconds). Within a few hours you will lose it all.

I have no real Idea but it sounds good doesn't it ?

3. Re: Hot Tub Heat?

It does, when I was standing out there thinking about it while the dog was runnin' around, my first thoughts were along the lines of yours. Then I thought... Naww, it can't be that easy.

P.S. I don't plan to do this now. Our pool is down for the winter and the hot tub is empty(not finished connecting everything). This would be more for next summer if nobody was going to use the Spa and we wanted a quick boost in pool temp.

4. Re: Hot Tub Heat?

Your spa is connected to your A/G pool? Do you mean they share water, or the spa spillsover into the pool? If so, I'd be fascinated to see how you plumb that so that you would only heat the spa water.... My point is that if you can heat the spa water, you can heat the pool water, too. if you plumb it right!

5. Re: Hot Tub Heat?

Yeah, they share the same water. I have 3 pumps between the two of them, but the way I plan to plumb it only one pump, the main pool pump(1 HP)which is connected to the filter, will have the ability to suck from and return to either body of water. The Spa Pack(1 HP) will only be able to suck and return water to the spa. All three pumps share one 3" suction from the spa, but the Spa pack has it's own 2" return to 4 jets. The third pump(1.5 HP) will only be able to suck from the spa but it can return to either the pool or the other 6 jets I'm going to add to the spa. I've attached some pictures since a picture is worth a thousand words...

Diagram I just drew. This shows the flow of the water and Valves/check valves...

Hand Drawn Diagram. This KIND OF show how it will look in reality.

Keep in mind, all of the pumps, and valves must be in this area, plus a blower and the sand filter.
This shows the correct position of the pool pump and sand filter. The other pump(jet pump) will not sit there. The spa pack will sit about where that is.

Thanks,

6. Re: Hot Tub Heat?

I planned the plumbing this way on purpose. I do not want to use the electric spa heater to heat the pool, at least not directly because, well, I don't think it could. If it could manage to heat the pool the electric bill would be astronomical.

Instead I chose to plumb the Pool Pump so that it could draw water from the spa or from the pool, and return it to the spa or pool. This way I can use the sand filter to clean the spa water instead of the cart. which I can remove(in favor of a skimmer basket) to improve flow. The other, and main reason for hooking everything up this way is so I can heat both the pool and the spa with the 120,000 BTU's of solar panels sitting on the roof.

The Pool Pump and the Jet Pump are on the same circuit so to ensure they don't run at the same time and overload it, I'm going to put them each on a timer and set them so the Jet Pump can't come on until the Pool pump shuts off. The Jet Pump is controled by an air button so it won't come on automatically, it will just have the ability to be turned on.

This may change if I put them on two seperate circuits. I'd still keep the timers, but it would just be so that no one turns on the Jet Pump while the Pool pump is still in Spa Mode. This would cause both pumps to fight eachother and push into a single 2" pipe with only 6 jets at the other end. Putting them on seperate circuits would enable me to run them both atthe same time. I'd be able to use the Spa and filter or heat the pool at the same time.

As you can probably tell, I've put quite a bit of thought into this whole build. Though, ALL imput and comments are ALWAYS appreciated!

7. Re: Hot Tub Heat?

That is an interesting approach. If you go that way, I suspect that you will need a couple more check valves. For example, I think the jet pump can currently flow backwards through the filter and pool pump and back into the pool that way.

There are a number of other ways to set things up, each has advantages and disadvantages. Is the spa going to be setup so that it can overflow into the pool? If so, you have the option of plumbing things in a more traditional way, perhaps some variation on this setup. If the spa doesn't overflow into the pool, you need to keep the relative water level of the spa and pool in mind, and it might be better to keep the plumbing more independent, set things up to switch the solar so it is either 100% spa or 100% pool and keep everything else separate.

8. Re: Hot Tub Heat?

No, the spa doesn't spill over into the pool. They just sit next to eachother and will be plumbed together. The Spa is sunk halfway into the ground. I'd guess the spa water level will be 1.5'-2' below the pool. I'd like to use as few check valves as possible because the one I have now increased my PSI by 1 already. The object was to only put them where it's most likely to backflow. Water can flow through the filter and all that, but I'm hoping the vacuum breaker on the solar panels will prevent a siphon from being created.

I redrew the diagram with more check valves. I also switched up the lower left area so it's drawn the way it will be plumbed in actual life. This is the "idiot-proof" way of plumbing it so that there's essentially no way it can back-flow anywhere. The first diagram was based on the system where only I'd be operating the pumps so I would manually turn the valves. The one with extra check valves SHOULD allow the rest of my family to operate this contraption with only 1 or 2 vavle changes, depending on what mode it's already in.

Anybody know about the temp gain from emptying it into the pool?

Thanks,

9. Re: Hot Tub Heat?

(104F * 350 + 80F * 4000) / (350 + 4000) = 81.9F. If your pool is warmer, then the rise would be lower (90F pool would rise to 91.1F). It's just a simple weighted (by volume) average of the temperatures since both contain the same substance with the same heat capacity, namely water.

10. Re: Hot Tub Heat?

Aright... so it's not much of a gain. 1*F is not worth the effort to drain it. I still need to exchange the water weekly(it it needed more often?) to get fresh pool water in there and keep everything from getting nasty.