Engineering a Domestic Hot Water System to Meet High Demand – GWC Mag

Hot water is a luxury no one wants to do without, especially in the winter. As GBA member bruckner1017 explains in this Q&A, to avoid that issue, he wants to replace his 50-gal. natural gas water heater with something that has greater reserves and is more energy efficient. He is thinking of an 80-gal. heat pump water heater (HPWH), for his shower-loving family of six, but he’s not convinced it will be able to keep up with the demand. He thinks that an electric tankless water heater such as the Autobooster or the HomeAdvantage II (both from Eemax) could be added to boost the supply, but he’s not sure how to size the capacity. He’s also wondering if a second HPWH would be better, but he’s concerned that his basement might get too cold in the winter.

The big question for this Spotlight is: What’s the best supplemental hot water solution for this family?

Hotter water? More storage? Fewer showers?

Not surprisingly, there are varying suggestions from readers. Referring to an endorsement from Matt Risinger, matthew25 (and others) suggests using a well-insulated electric water heater made by Marathon as a backup that would run only when needed. Paul Wiedefeld likes that idea, and adds that drain water heat recovery might help to make the HPWH more efficient. He and others also suggest low-flow shower heads as an inexpensive way to reduce consumption. Another proponent of that low-tech approach, nynick thinks this is a good opportunity for a family meeting to talk about water usage and per person water-flow rates.

Occupant behavior aside, acrobaticnurse_Eli recommends buying an even larger HPWH, while Rearmiend suggests consulting the Department of Energy’s information on water heaters.

The idea of a supplemental tank is a common refrain,…