willworkforwood said:
I know that gas tankless DHW has had big-time usage outside of the US for a long time, but I didn't know anything about the electric version, so I took a look at them on the web. They have a well-constructed site which makes it fairly easy to get a quick estimate of what's needed to get it done. Based on the fact that electric water heating technology has been around for a long time, it would seem to be fairly bulletproof (I saw a mention of lifetime warranty for some of their models). So it probably comes down to the purchase/installation cost, versus what you would save per year * expected years living there. Would you be replacing an electric tank, or is it fossil boiler-based DHW? One obvious question is usage - is it fairly low for your household? It's fairly low for ours, and it sticks in my craw that we need to have a giant tank of hot water "standing by" 7/24, for just occasional use (along with a non-condensing boiler that also needs to always keep itself hot). Another by-product of (formerly) cheap oil resulting in our country standardizing around a wasteful DHW technology. Have you also considered the possibility of solar DHW? I kick myself often for not installing solar years ago - it would have paid for itself multiple times by now.
Thanks for your thoughts.
Its sort of complicated. We heat the house with wood and an electric geothermal heat pump. We don't have gas or oil but could get it, but don't want to.
We started with two 40 gal. electrical resistance water heaters, one serving the master suite including a Jacuzzi and located upstairs in a closet, and the other WH serving the rest of the house and located in the basement. The basement is a long way from the master bath.
I've replaced the WH in the basement with a GE Geospring heat pump unit which I run in heat pump only mode. My plan is to combine the now split systems and put everything on one source. However, that one "source" will be, in sequence, Solar


GeoSpring (in basement)


> Tankless electric (in upstairs closet). The solar water heater will likely be a relatively simple "pre-heating" system" without pumps, etc. The tankless unit will be installed so that it serves only the 2nd floor bedrooms including the master. Keep in mind that water entering the tankless unit comes from the solar/HP WH in the basement. The kitchen, downstairs bath, and laundry would be served by the solar and HP WH (not the tankless).
Here's my reasoning. The choice of solar is obvious. The HP unit is already purchased, in use and produces cheaper hot water than the tankless. The tankless will allow us to have hot water quickly and in sufficient amounts to fill the Jacuzzi or during other times of heavy usage (e.g. guests).
There are other considerations I'm not mentioning here that have to do with hard water, basement de-humidification, wiring, plumbing, layout, etc. BTW, it seems that heating hot water is our main usage of electricity which is why I'm spending so much time on this. I also hate using the Jacuzzi half full.
I welcome feedback on the plan. I'd sure hate to waste my time and money building a system that doesn't work well or save some power/money. A long payback period is okay.