Years ago, we got Conan the Hot Tub, so named for who paid for the appliance.
Actually, that's a misnomer. Back in the day, a hot tub was a big vat full of water without any circulation vis a vis pumps or jets. You cranked up a heater (or built a fire in a metal box that extended into the water) and that was it. What CtHT was was actually a spa, since it had the bells and whistles. Or bubbles and jets.
What it didn't have was a heat governor on the top end. You could dial the water temperature up or down, and on the high side, it got far too hot to get into without burning yourself.
After a short period of acclimation, started with the pregnant-women-no-hotter-than-102º F. setting, I found I was most comfortable at 105º-106º F. I could sit for fifteen or twenty minutes at that heat and enjoy it.
105º is what nurses are taught is the maximum temperature for bathing hospitalized patients, or it used to be when I trained.
Eventually, we passed Conan off to my son, where he sits unused in the back yard, and got a new deck and a smaller model, since it was just two of us. The advantage is that it cost less to heat, being smaller. The disadvantage is that the system is hard-wired to a maximum temperature of 104ºF. Can't get around it without jury-rigging some kind of bypass, and that's not something I'm willing to do.
Apparently that is the maximum for legal liability these days.
So, still not bad. Problem is, because there is less water, it cools off faster, and on a cold day, it drops a degree or two pretty quick, and 103º doesn't feel really warm.
102º feels positively cool.
Yeah, yeah, the ashtray is full in the Rolls, oh, dear, best I get a new one.
Now and again, I must add water to the tub, since some leaves with me, some evaporates, and some permeates the lid. Every week or so, I plunk the garden hose in, top it off, and there you go.
When it freezes, the garden hose is useless, so I've got a five-gallon bucket I can fill in the shower or tub or even the outside faucet for this chore.
Hey, I realized first time I did this. Here's an idea. What if I filled it from the hot water tap in the house? Would that be enough to make a difference?
Yes. One bucket of hot-as-it-gets water from the inside bathtub is enough to kick the overall temperature up to 105º, which is ideal.
Sometimes, the solution is as easy as that.