Pool and spa - separately maintained heated water or not?

[mike_in_menlo]

We are soon going to be starting to dig. I met with my PB yesterday, and was asking about heating the pool and spa. He says that the way they usually set them up is that they're typically both kept at the same temperature, with essentially shared water, I assume filtered together. You can then push a button, a valve will switch, and the spa will be heated exclusively, so that you can get it to a much higher temperature.

I'm not sure I like this setup. In the winter, for example, I'd love to leave the pool water unheated, and keep the spa and 70 or 80 or whatever, so that we can heat it up to 100 in not too long. Note that I do *not* have a spillover, so I'd think the water could be kept somewhat separated...

I asked if they could be maintained consistently at separate temperatures, and he said
"We can set the system up that way, but there are issues with maintaining the water level, and chemical balance."

I'm going to chat with him about it the next time I see him, but in the meantime - can someone clue me in on what the difference might be?

Does anyone plumb their pool and spa the way I described, where it's easy to maintain the spa at a much higher temperature than the pool?

Thanks!

 

[jblizzle]

Not usually. The way the builder described is normal. It should not take very much time to heat the spa up if the heater is properly sized.

 

[JasonLion]

By far the most common solution is to use shared water and shared equipment, which requires keeping them at essentially the same temperature except for fractions of a day when you heat up the spa and use it as a spa. With such a setup it is possible to leave it in spa mode all the time and keep the two bodies of water at different temperatures, but if you do that the pool won't get any circulation/filtering at all and the max water level in the spa needs to be a bit lower than usual. Also, with such a system there is always a "spillover", even if it is completely hidden, i.e. water above a certain level in the spa will flow from the spa into the pool, though you may not see it do so.

Another kind of setup is to have two completely independent bodies of water, two heaters, two pumps, and two different bodies of water that must be balanced and sanitized separately. This is more expensive, but allows you to do anything you want with each body of water separately.

There are also a couple of different setups with some aspects of each of those two options, but none of them really get you the things you are looking for without being even more expensive and complex than the two independent setups approach.

 

[mike_in_menlo]

Thanks for the replies.

He's putting in a 400K BTU Starite heater, which I assume is plenty big enough for my 6'x8' rectangular spa. He mentioned it may take a couple of hours to heat up in the winter. Maybe that's assuming the regular pool heater is off, and my pool water drops to say 50 degrees (? - we're in Northern California / Bay area).

 

[JasonLion]

Say the spa is 500 gallons, that is roughly 4,000 pounds. One BTU can raise 1 lb of water by 1 degree fahrenheit. The heater is about 80% efficient, so 320,000 BTU/hour effective. That means that that heater can raise the spa temperature by 80 degrees in one hour. Of course that assumes no heat loss to the environment. In practice heat loss will increase as the air temperature goes down and the water temperature goes up, so it could easily be more than an hour to heat the spa from 50 degrees to over 100 degrees. Heating will be faster if you keep the spa covered, but even then there will still be noticeable heat lost to the ground.