Our rental unit is constructed using strawbales. We heat it primarily with the same solar collectors that are used to preheat the water. See my articles on building an alternative home and building using recycled paper for other information.
One of the objectives when building for rental purposes, besides safety, low maintenance and longevity, is lowering the operating costs. If the heating costs are kept down, the margin of profit can be raised. This can be accomplished by using solar for water and interior heat.
I found a plumber who had a problem and we both benefitted from the solution. He had a yard full of water heaters with bad heating units, both gas and electric. He said the pressure vessels were still good and so was the rest of the heater, including the outer shell. I didn’t need the outer shell but it was recyclable at a scrap metal yard.
I made an adapter so I could hook the pressure vessel to a garden hose and fill it with water and pressurize it to check for leaks. The adapter is easy to make, just use a piece of hose that has the female end that screws to a faucet, cut it off about eighteen inches long and put another female hose fitting on the cut off end. This gives you a piece that has two female ends and can adapt to most water heater connections. You may have to buy a pipe to hose adapter which is available at hardware stores. It may be possible to hook directly to the water heater but that wasn’t the case with the ones I got.
After checking that the heaters held pressure, three were painted flat black and placed horizontally end to end, plumbed together and then into the rental unit hot water system on the delivery to the electric water heater side. The water heaters are inside a clear fiberglass housing on the south side of the rental unit. Four inch PVC pipes are run vertically and go through the south wall. See photo for details. On the interior side of the rental unit wall, there are PVC caps that can be removed to allow for heat from the enclosure, and water heaters, to rise and enter the rental unit. Water is a good solar mass and heat is delivered passively into the rental and used to heat the water, 24/7. I also use entryways with security doors for heating in the winter as explained in my article “Heating and Energy Efficiency Through Solar Gain”
During the summer, the vertical pipes from the water heater enclosure are blocked off. Ninety degree elbows, and a piece of PVC pipe long enough to clear the roof top, are added to the pipe on the exterior where the caps are in the picture. Screen is placed over the open ends so no bugs can enter the interior of the rental unit and the interior caps are removed. The interior caps are just below the ceiling where the hot air rises to in the summer. The hot air is sucked out passively, heat rises, and the building is cooled. This works especially well at night when the temperature of the interior is much higher than the air outside. When the security doors are locked and the interior doors are left open, cooler air enters at floor level, is heated by the warmer interior and rises to the ceiling where it is sucked out. In the summer the system works to help cool, in the winter it helps to heat and all year it lowers the costs of heating water. I wish I’d thought about this system when building the house. It works very well and I may add to the house at some time in the future.
I flushed the heaters out before installing them by using an eight foot length of four inch PVC pipe. I put caps on the ends that had been drilled and tapped to accept a pipe fitting on one end and a hose fitting on the other. A gallon of chlorine bleach was added to the four inch PVC Pipe and the PVC pipe was hooked into the heaters with the garden hose adapter. The bleach and water mix was flushed through the system until chlorine could be smelled at the outlet side of the heaters. It was left in the heaters for a few days and then flushed again until all the chlorine smell was gone.