Tankless Water Heater
Q: Can anyone tell me if they have had experience ( good or bad) with the 125 series AquaStar by Bosch tankless water heaters. They look real good on paper. Also does anyone know how they handle extremely hard water. Bosch say just remove exchanger, soak in vinegar, and re-install. Do this every couple of years.
A: I'm interested in experiences with various tankless/solar hot water systems. Ours just burned out (Myson tankless) after the vent was buried in snow. I might try to fix it, but I'd like to know what the other experiences with Aquastar, Paloma, etc are. We are a family of 4 on propane with water efficient appliances planning to install solar DHW in the future, so this will revert to a backup some day. On the other hand, I might just go ahead an install a tank intended for solar hot water, so that we just hook up the panels and piping and we are done. Any experiences with either tankless or solar/propane hot water heaters? My wife likes hot water, so your timely response would be most appreciated! I had the smallest Paloma once - hanging on the side of a cabin, heating one shower. Worked fine for that if the water was cold. (As long as you remembered to drain it before freezing weather!) Once I added a solar collector, there were way too many times when the water was too cool for a shower but too hot for the Paloma to be able to stay on, even at its lowest setting. When I designed my real house, there was also an issue of where would a tankless flash heater "live", so that it would be protected from freezing yet have access to the required combustion air. The Myson direct vent was the closest to solving this problem, but it relied on a standing pilot - which I was hoping to avoid. Obviously you have freezing temperatures to deal with. I struggled with each of the solar freeze protection systems in turn: The dribble valve wasted too much heat and too much water and eventually buried itself in ice anyway. To get the water up to the roof, the drainback system needed a big pump that was too noisy and too power hungry to run on PV. The draindown valve couldn't handle my hard water and needed continuous attention. Filling a whole heat exchanger tank with antifreeze would have been too expensive, and disposing of all that used antifreeze didn't sound very "correct". I've ended up with a system I believe solves all these problems. There is a "primary loop" with antifreeze which runs through the input coils (five parallel 50' coils of copper tubing) of my exchanger tank, fed by solar collectors on the roof, a water heating woodstove outdoors, and an outdoor propane fired (Seahorse) water heater. The exchanger is a "dead" unpressurized tank with corrosion inhibited water which serves only to store (and exchange) heat. My domestic hot water passes through another set of coils in this tank, to be heated on-demand from the stored hot water. The Seahorse heater is automatically spark ignited when it needs to run, and installs outdoors with no intake or venting problem, so plumbed into the antifreeze loop it make a great backup heat source that can can sit idle until it is needed. They are intended to retrofit electric water heater tanks to burn gas, but are often used as the smallest hydronic boiler in mild climates. I suspect they would be vulnerable to being buried in snow, but they have a built-in high limit shutoff to prevent burnout. Everything that can freeze is running antifreeze, but it only takes a couple of gallons to fill the primary loop. The exchanger tank never sees my hard water, or the fresh oxygen in a moving stream of DHW, or the temperature stress of being directly heated, so it should last forever. And it is unpressurized, so if it should fail the mess will be minimal. Plus there is no lukewarm tank of stagnant DHW breeding bacteria and slime - I can cook and make drinks with the clean, fresh, instantly heated water from the hot tap! If there is solar heat available, the other sources don't run. If the day ends without collecting sufficient solar heat, a backup source can add just enough heat for comfort. If I wanted to store more solar heat, all I'd need would be a larger tank of dead, unpressurized water. Other heat sources, or hydronic heating circuits, could be added to the primary loop without much disturbance to the existing system. I was concerned about the efficiency of the double heat exchange required in this system, and I probably went overkill on the amount of tubing I used, but I've been extremely pleased with the result. With a 3 GPM flow and 90F rise, the DHW comes out within a degree or two of the water in the top of the exchanger tank. Like many energy-efficiency schemes, this is not the cheapest solution in the short run, but after all my firsthand experience with the problems of lesser systems, and given that most of the components should outlive me, I think it was money and work well spent.
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