12) Hot Tub - Small but Beautiful
The hot tub is the most problematic element in the planning of the SunCottage. Originally we were thinking it would be located inside the house, either on the main or bottom floor. But issues of humidity ruled out this idea pretty quickly. The web is full of in-house hot tub horror shows.
OK, so it's going to be outside... but there are a few problems with that, too. The biggest being that it get pretty cold out there in winter in Vermont! Heating hundreds of gallons of water when the outside temperature is below zero would put a big load on the geothermal heating system. Not to mention that while some love the idea of sitting in a heated spa while snowflakes fall in the water around you, I personally hate the idea of walking through the foot deep snow barefoot to get there.
We came up with a compromise: an enclosed hot tub room attached to the house but outside its air-tight heating envelope. No humidity problems! No walking on ice problems! The room could be built with plenty of windows so, if you chose, you could open them wide and it would be just like being outside. And then there's the NanaWall, a 12 foot foldable door that can be opened for full exposure to the southern sun:
At first we were thinking that the hot tub should be built-in, in concrete, at ground level. But it was actually my brother that dissuaded us from this idea. His view that for access to the piping and controls, and for ease of possible future replacement, it would be much more prudent to buy a commercially available model. We bought the logic.
In looking at the various manufacturers and models we quickly keyed in on the Jacuzzi J-210. We liked that it was round, frankly I don't get square hot tubs. Secondly, it has a really low water capacity, which is important when you're considering all the BTUs that it takes to keep it at 104°, yet can fit up to four people. Needing only 225 gallons of water (compared to party spas which range up to 500 gallons), we think it's perfect.
Besides the fact that outside hot tubs consume a lot more energy than inside ones, a big issue is that you can't drain them if the temperature is below 32°. You simply can't have the pipes freeze, they'll burst and essentially destroy the hot tub. We're hoping that by having the tub in an insulated room we can keep the temp to avoid this problem. We can open the inner doors and let heated air into the room, and of course we'll be gaining a lot of solar heating through the Nanawall, but we're not going to really know till we get to test it out in live conditions. Another possibility is installing a small electric heater in the equipment area. Perhaps insulating it as an enclosed surround. Either way we plan to drain the tub between visits. To keep the tub at ground level we designed the hot tub room to be three feet below the basement level. The idea is that a deck will be built up around the tub. A hatch will allow access under the decking to get to the tub's inner workings when necessary. Our designer, Tim Ouelette, came up with a novel idea: make the decking itself out of 2 foot by 2 foot concrete plates painted white on one side and black on the other. The idea is that in winter, you put the black side up, to absorb solar radiation, and in summer you reverse them to reflect. I love the idea! How about this: you flip them over gradually, so at the solstices you have a black and white checkerboard?
How much energy will the tub consume and how much will it cost? The J-210 specifications say 100 kWh per month for a cost of $15. But this clearly would be affected by the room temperature, the temperature you set the water at, and the amount of use. Something I didn't realize is that running the jets quickly lowers the temperature of the spa water, apparently heat just flies out with all the bubbling and spurting. We don't expect energy use to be a problem except in the deep of winter when the sun is low, electricity production is low and the outside temp is low. Should conditions allow we're thinking that we may drain the tub and shut it down completely if say it isn't expected to be used for three weeks or more.
The Spring
OK, we have the room and the tub... what about the water? Having been a property manager in the past and being responsible for people's hot tubs, I have an aversion to bathing in other people's used water. I've seen people get sick, how can I forget the time an entire condo contracted a nasty red rash? (Note: the maintenance was the responsibility of a third party, not me!) In any event, I always believed that the water in a hot tub should be fresh for each person's use. I learned subsequently that this is now the standing operating procedure. Good.
We are fortunate to have a spring on the property that produces 5 gallons of pure fresh water per minute. Even better is that it is uphill from the hot tub room so we can pipe its water to gravity feed into the jacuzzi And here comes the interesting part: if we put a spring water reservoir in the basement, we can pre-heat the water to room temperature, rather than using straight-from-the-spring water at 50°, we'll be a good 20° warmer. Thus more than 33% of the way to our optimal hot tub temp of 104°. I addition, the reservoir will allow us to fill the tub in a matter of minutes.
We're lucky to have on hand a 500 gallon container donated to us by the Vermont Farmstead Cheese Company that we plan on using as the hot tub reservoir. It's about 3' x 4' x 4' in size:
We also plan on supplementing the reservoir's temperature with a solar hot water heater, something along the lines of this evacuated tube array:
This technology has come along way from the black painted box with tubing that people were using in the '80s. Evacuated tubes can produce 170 to 250 degree water even during the coldest winter days!
See Evacuated Tube Collectors for more info
