Bathtub water re-heater
 

Just had an idea wilst having a soak... if you have a jetted bathtub, could you not T-in to the jets with a line to a 'quick' water heater of some type?

The reason I thought of this is, when you're having a long bath and it eventually cools off, what's your first instinct? Drain some water and fill it back up with new hotter water right??? So not only are you paying to heat more water, you're also paying more for the additional water, as well as the sewage bill to pay for the water you're dumping down the drain!

So if you could plumb in some kind of circulating heater in the tub, you would at least lessen the amount of water you consume right? I'm sure there has to be a smaller more efficient way of heating smaller quantities of water on demand than a hot water tank. (maybe pull off of your solar hot water resevoir? :)

Pattent Pending... :P

Not a bad idea at all. :)

I would worry a little about residue on the heating element building up, but that might not be a problem.
You could also get a heating pad for an automotive oil pan and stick it to the underside of your tub of it's metal then insulate around the underside with reflective insulation.
Some people also build insulated covers to help keep the water warm.

My Jaccuzi has this.
Broken, not installed Jaccuzi.

Basically, you are trying to reinvent the hot-tub.

Which is fine. I think it's a good idea. It would have to be a pretty big heater though, it might not be practical unless it was 240V.

Seems like all the spa heaters are superheavy duty - hard-wired straight to a dedicated breaker.

Yes like dremd said you already buy these, check plumbing store

I did this years ago using one of those automotive canister heaters designed to heat the cars engine. The units work from 120 volts and are designed to thermosiphon. I had made a soaking tub and used one of these in that manner, the tub temp stayed around 105.

mike

I have a few of the things you describe already. The universal one I have in the garage is a heating element gleaned from a coffee maker plumbed in series with a positive displacement pump from a big green clean machine. The thing is self priming, uses the coffee maker thermostat, and doesn't even have a switch. Truly simple plug and play Operation.

For indoor use, the snap disk (klixon) thermostats can be found in just about any temperature range you might want. The coffee maker heaters are pretty darn durable and are connected to the rest of the coffee maker with high temperature rubber hose. To select the proper heater for your application, just look at the nameplate on the back of the coffee maker. The wattage rating is the heater power. To avoid having to prime the thing, go for a positive displacement pump. If you're picky about noise, some creative sound isolation might be needed.

I saw a tub with a water reheater at the big box hardware store last month.

Don't forget the value of insulating the bath tub.

Most of the heat loss is through the sides & bottom.

You might find that by conserving the energy present in the hot water, you can have the long soak you are looking for with out needing to add any more energy.

-AC_Hacker