Geothermal Hot Water +/- On Demand +/- Circulation System
Hi all - as we progress in the actual building of our dream house on a nightmare lot (anyone want about 500 landscaping boulders?), we are nearing a decision point about something I've been obsessively reading about for months...
We are definitely doing geothermal, and the installer recommends, of course, taking advantage of the free hot water with a 100 gallon holding tank. I know that the actual temp of that water will vary (though should never be cold) by sesaon, so we planned on adding an on demand heater (Rinnai, maybe) as well.
I seem to think that putting the on demand heater in series after the holding tank would make most sense, since it won't kick on (I think) if the incoming water is already hot, and even if it isn't hot enough, the temp change (delta) will be less than a cold feed, making the unit work more efficiently...
The issue we worry about is adding a circulating system to the house, and where to pull that feed from. I don't want the on demand heater running constantly just to circulate water, but can I have a second feed coming from the holding tank, so that we circulate at least warm water, in the worst case scenario?
I've asked around, and every professional installer has a different opinion of what "should work."
Another issue is that we have an in-law suite (+1 small bedroom/bathroom, 2 total BA) set up over the garage, which would have a very long run. We've considered putting a second on demand unit (lower capacity) right under it in the garage, but then using that unit for the in law suite, as well as the washer and dishwasher... My only concern there is that we'd then be using instant hot for the washing machine and dishwasher, even when we could be using the free hot water from the holding tank during part of the year. At the same time, if we have only the holding tank and one on demand unit for 4 1/2 baths and the washers and dishwashers, we may max out capacity...
Our plumber also told us that we'd need larger than standard pipes if we don't want to add the second heater under the suite, which would kill any savings of not buying the second heater.
We have 6 1/2 baths, 2 dishwashers, and a washer. We may add a second washer in the basement down the line.
Any thoughts on solutions? I just can't find any good resources that aren't selling their solution! Imagine that. :)