Tasha and I had been planning on putting a hot tub in the greenhouse since before we had a greenhouse. We had always intended it to be a source of heat during the winter, but more importantly, as a means to soothe away the aches and pains of a hard day’s work on the farm.
When finally our long-awaited hot tub did arrive a couple weeks ago, I had to wait another week to assemble it becuase they sent us the wrong size hoop rings…Grrr!
Getting the tub assembled was a bit tricky, and after a couple of tries at standing up the staves, the best I could do was a slightly lopsided arrangement where one side inevitably ended up with a row of staves with a 1/16 inch gap between them. On my third or fourth try I finally let it go. Then it was on to the chimney…
Running a chimney through a polycarbonate greenhouse roof proved to be a little bit of a challenge. It was easy enough to cut a hole in the roof panels, but the chimney would have to be insulated in order not to melt the roof where it passed through. For this, I bought an insulated chimney section and ran it through a pre-built flashing box, which I also bought at Lowe’s.
In order to make this work and get a reasonable clearance of the stove pipe over the greenhouse, I bought more stove pipe to cut to length–about 14 inches–between the wood stove and the chimney insert running through the greenhouse roof. Where the top of the chimney insert passed through the flashing box, I adjoined the six feet of heavy gauge-stainless steel stove pipe that came with our hot tub.
This got some nice clearance–to code, and then some–over the greenhouse roof, but it also added about a hundred pounds of weight between the chimney insert and the top of the stove pipe. We live in a high-wind area, so seven feet of stove pipe can be a liability if not properly anchored.
For this, I screwed some sheet-metal strap to the ridgepole of the greenhouse roof, stabilizing the smokestack in one direction. In the other direction, I sank some metal stakes into the ground and ran guy wires. So that took care of lateral stability, but I still had a lot of weight coming down onto a narrow-gauge pipe that connected the stove to the chimney, and this was worrying me, since I didn’t really have any framing members I could anchor the chimney insert to.
To make things even more difficult, the aluminum wood stove that sits submerged in the tub comes with a stainless steel cover that is designed to be anchored to the tub rim about 10 inches above the stove top, but not to support any serious downward weght. To fix this, I built a platform out of angle iron that our solar installation contractors had left lying around, and I got to use our recently purchased angle grinder and drill press in the process. The otherwise flimsy sheet of stainless steel now had some support under it.
That gave me a bomb-proof platform on which to build a a lighter but similarly designed frame to take the weight of the chimney insert and stovepipe. I built this with a couple pieces of flat and angled aluminum stock that I picked up at Lowe’s, again using the drill press and angle grinder. All of this could have probably been accomplished with a few good welds, from the chimney insert to the aluminum greenhouse frame, but I don’t yet have those skills. Anyway, this worked out for us, though it took some thinking about.
When finally it came time to fill the hot tub, we couldn’t because the water would run out through the gaps in the staves as fast as we could fill it. What to do?
I looked at the (very poorly written and illustrated) manual for some troubleshooting advice and came upon this gem: Throw in a handful of sawdust. This is supposedly an old tub-builder’s trick that apparently works by creating a temporary seal between the staves, which enables the tub to hold water long enough for the cedar staves to swell and shrink any gaps between staves. Well, this is what I did and after a few hours, I was surprised to see the tub holding almost 400 gallons of water.
At that point, we were able to heat the water, thus increasing the swelling of the wood. The next day I was even more surprised to see the level of the water just barely decreased, with hardly any discernible leaks. After a week, the tub is still water-tight, and has so far provided us with several good soaks.
Tasha moved the pile of cardboard that was sitting in the other corner of the greenhouse and put down some pea gravel, which keeps the area from getting muddy when people get out of the tub and adds a lot more visual appeal. She added a couple solar lights, moved our table around to give us a nice place to sit between using the tub, and now we have a place to stack wood too.
As far as heating the greenhouse goes, it seems to be contributing somewhat. The water the next day after using it only loses about 5 degrees overnight. I’ve read several places that keeping a couple 55-gallon barrels full of water acts as a heat sink and helps to stabilize the daytime/nighttime temperature differences. So we’ll see. So far, we’re definitely enjoying it for its primary intended use.
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