I’m curious if anyone has tried this setup for efficiency with instant hot water or knows why it wouldn’t work. I’ve never heard of anyone doing it, but I’m considering installing an electric instant hot water heater inline after a simple storage tank.
Why? Well you generally size instant hot water tanks regionally to match worst case expected groundwater temperatures. Where I live (Northern United States), that can be 40F in the winter and you basically need the strongest unit.
My idea is a buffer tank - could just be an old hot water heater, maybe a modified rain barrel or other unit that can hold suitable water pressure. It would come up to room temperature during the day along with everything else via the existing HVAC system and provide 60-70F water to the electric heater, which has much lower power requirements to then boost the up to shower/usable hot water temps.
Depending on tank size it could work for a while before the tank matches groundwater temp. During the coldest times of year, 50 gallons would last 25m at 2gal/min but really that’s saying I would have replaced all 50 gallons with groundwater while mixing them so you’d have to use significantly more than a full tank for the buffer to become the same temp as the groundwater. Probably 1.5-2x so between 40-60 min of showering, which seems like more than enough to be worth the comfort and smaller heater size.
Has anyone tried it? Is this worth the trouble?