As part of my renovation project, I needed to move the water heater out of its location in a below-grade recess in my crawl space that I was filling in to eliminate the need for a sump pump to get rid of water that collected. When considering the best type of new water heater, I considered both heat-pump water heaters and tankless heaters.
One thing I like about heat-pump heaters is their dehumidification capabilities, but after some discussion with others who have installed them, I determined that the amount of hot water I use would not cause the heater to run frequently enough to provide any significant amount of dehumidification. It would also have to be installed in my new storage room, which didn’t exist when I had to change heaters — a fact that would have required me to move out sooner than I planned.
My next option was to install a tankless heater on the exterior of my house, right next to the bathroom. This was a task I could do before demolition started, allowing me to stay in the house through the first half of the renovation work.
Considering going all electric
The heat-pump water heater was part of a strategy to eliminate my natural gas use. I had already installed minisplit heat pumps for space heating and cooling, so the only natural gas used is for water heating and cooking. I could have replaced my range with an induction unit and eliminated my natural gas connection altogether.
Down here in coal-burning country, that seems like a poor decision in the climate change department, particularly since I have no solar exposure to take advantage of for PV panels. I can purchase green power from the local utility, which I will get around to doing sometime soon to assuage some of my guilt.
The main reason for dumping natural gas was purely financial. Although we have low natural gas rates, the monthly base charges are pretty high, so although I use about $1.00 worth of gas a month, I end up with a bill of about $28.00 of recurring non-fuel charges. Pretty annoying.
I could have used an electric tankless heater, but I have not heard many good stories about them, so I went with a gas tankless heater. The Rinnai unit I installed was mounted on the exterior of the bathroom wall, a bit closer than the old tank heater, but when I first used it I discovered that the start-up time allowed one half gallon of cold water through the line before any hot water arrived.
I have learned a lot about hot water distribution from my friend Gary Klein, the guru of all things hot-water-related, so I discussed the situation with him and came up with a plan.
A good plan, at least in theory
I installed a main hot water line that ran past the shower, lavatory, and laundry, and ended at the kitchen sink. That’s where I installed a Metlund demand pump with buttons to activate it in both the bathroom and kitchen.
Between the heater and the shower, I had my plumber install a 3’ length of 2” pipe as a reservoir for hot and cold water to mix. Since the gas tankless heater always has the half gallon cold start, the intent of the reservoir was to buffer that cold water “slug” and avoid waiting for hot water at every use.
All looked good until I took my first shower. I ran the demand pump to prime the hot water line. When the pump stopped, I turned on the shower and the water was hot within about 15 or 20 seconds, wasting about 6 or 7 cups of cold water – more than I wanted, but not terrible.
Then about 30 seconds in, the water ran cold again for another 30 seconds. Although 30 seconds does not seem like a long time, when you are naked in the shower and the water turns cold, it sure seems like forever.
Time for some testing and investigation
I ran the shower with and without the demand pump and checked the water temperature with an IR thermometer and a timer. Interestingly, hot water arrived at the shower in about the same amount of time whether or not I used the pump. The big difference that was without the pump, the water heater never turned off, avoiding the ramp-up time, keeping the water hot throughout the shower.
Further discussions with Gary as well as Larry Acker at Metlund led us to the conclusion that the buffer reservoir I installed was both too close to the shower and not large enough to balance out the water temperature. The demand pump works well when running the dishwasher or when I need hot water at the sink, but it just isn’t doing much for the shower at all. If the distance between the water heater and the shower was longer, and the reservoir larger, it probably would have done a better job managing the temperature.
Had I purchased a tankless heater with an internal buffer tank, I probably would have avoided the cold water slug issue entirely, and in my endless quest to waste money on my house, I may consider swapping out heaters and seeing if the demand pump works better. But for now, I will just waste a bit of cold water when I take my showers and only use my pump for my kitchen. Another lesson learned.