Any good reason not to plumb my hot tub so that I use my hot water boiler to heat it. My thought was to set it up so that I would completely switch between house heating and tub heating, and that I would completely purge the boiler when switching between functions. Tub heating would only be occassional, but would be the normal function in the summer when I don't use heat. Plumbing is all copper in the boiler now. I don't use additives in the boiler water.

This seems to me like an energy efficient and fast heating solution for me. I don't mind the hassle it would involve. But I'm specifically wondering if chlorine in the tub water, or some other issue, might make this inadvisable.

Thanks.

 

You would have to use a heat exchanger. Getting the temperature controls to be tight enough to temperature would also be an issue.

You could possibly do some surface heating to the underside of the tub with PEX and leave the electric for fine tuning. This way you could spare the expen$es having to buy a heat exchanger and a stainless steel circ.

 

Would I need a heat exchanger because the chlorine would disturb the boiler, or because the boiler would contaminate the tub (and what with)? The boiler is about 15 years old, 80K Dunkirk I think, off warranty. Would I really run into trouble if I purged the boiler between uses?

 

Contamination could occure in either direction, but I would be most concerned about the chemicals, air and dirt (sweat, dead skin, hair, body oil...) in the tub water. I think you would find it to be a fast way to end the life of the boiler.

With it's cover in place, the hot tub should be a fairly efficient unit without any creative plumbing. I doubt that anything you do would save enough to justify the initial expense or the later expense of repair.

Doug M.

 

I agree with WHO & DougM. The chemicals in the hot tub water would spell a quick death for your boiler. The cost of a heat exchanger & the related accessories would not be recovered in energy savings vs using the electric heaters built into the hot tub.

 

ok, thanks guys. you've rescued me from diy halfassedness.

 

You would need a HX beacuse the hot tub would be an open system. It has oxygen in the water and this would rust pretty well anything that it was connected with. By using a HX you separate the open system (hot tub) from your closed heating system. On the open system side, you would want to use all non-ferrous componants including a stainless steel circulator. Otherwise it would rust really quickly.

By running some PEX into the enclosure but not actually mixing with the hot tub water, you keep your heating system closed.

Some pool heaters are just HXs. The use the pool pump to move the water through it on the one side and the other side is the closed heating system.