Heating a hot tub

JetMech

I was thinking of ways to reduce some of my electric costs and my hot tub came to mind. I'm assuming that solar-heating the water would be more economical and efficient than using solar-electric to run the tub's heater. I did a quick search and saw some hot tub kits which seem reasonable buy were basically just a collector and a pump. Since I live in Connecticut, wouldn't I need a closed-loop system? I use the tub all year long but it seems like I would have to drain it if the water from the tub was the same fluid pumped up to the collector.

Cariboocoot

Re: Heating a hot tub

Yes; electricity is a lousy way to heat anything.

As for solar in Connecticut ... how much sun would you get in winter? You are quite right that some provision for freeze protection would be necessary, but any time you have to transfer heat value (as in a closed system of anti-freeze heating the open water of the tub) you lose efficiency. Hot tubs are a very large volume of water requiring quite a lot of heat input.

You may find that propane is your friend on this one.

icarus

Re: Heating a hot tub

An issue that I have thought a bit about before,,, but never done anything about.

It seems you could run a simple flat plate or evacuated tube collector with a glycol loop into a smallish hot water heater tank (or other insulated tank) 20-40 gallons. control this with a simple differential controller.

The plumb your hot tub with a loop into that tank, so when the t-stat on the hot tub call for heat, the tub can circulate and pick up heat from the tank. It seems the reason you wish a tank to be small is that you want it hotter than the tub temp as often as possible. Too hot (within reason) would not be a problem. You would probably wish to have two stats and two circ pumps so that in the event that the tank temp was too low, the tub could use it's own heater and not run the risk of cooling off the tub water into the glycol tank. Instead of two pumps, you could use a couple of solenoid valves instead.

A system like this would have some complicated plumbing, such that you would have to cut open the current hot tub system,, but it certainly would be doable.

Let me know how it works,,, if you do it.

Tony

My hot tub is a galvanized stock tank with a submersible "snorkel" wood stove in it. In the summer it sit on the shore,,, in the winter on the ice. We fill it with ice water out of the lake,, and in ~8 hours it is hot. With an insulated box the temp only drops to ~80f overnight so it only takes ~1 hour to get hot the next day. We use this tub almost every day,, and change the water about every 4-7 days. No chemicals or filters. Works great.

LucMan

Re: Heating a hot tub

JetMech wrote: »

I was thinking of ways to reduce some of my electric costs and my hot tub came to mind. I'm assuming that solar-heating the water would be more economical and efficient than using solar-electric to run the tub's heater. I did a quick search and saw some hot tub kits which seem reasonable buy were basically just a collector and a pump. Since I live in Connecticut, wouldn't I need a closed-loop system? I use the tub all year long but it seems like I would have to drain it if the water from the tub was the same fluid pumped up to the collector.

The easiest way would be a small closed loop system with glycol, & heat exchanger. This would allow year round use.

JetMech

Re: Heating a hot tub

Getting at the tub's innards isn't a big deal, the sides are just wood panels that are held on with screws. Solar roof's has a setup that looks like it may work.