Help designing a radiant / DHW system for a small home

hot_rod

doughpat said:

I am intrigued by the point of use fixture. I'm curious how much of the heating load it ends up providing. It "seems like" it might end up providing quite a bit, considering how often the kitchen faucet gets used for just brief periods. Washing hands, a quick dish-wash, etc.

I suppose that it doesn't help reduce the number of on/off cycles on the Lochinvar combi. The combi is going to fire up any time hot water is called for. The point of use heater will just reduce the amount of time you have to stand there and wait for the hot water to arrive. In fact, I could see it being even harder on the combi, as the water will be shut off even faster....before the combi really even gets going?

Do they require a dedicated circuit? I've got the walls open now and running a circuit (even 240V one) would be relatively easy now...

Yes it's mainly a small storage space to eliminate that cold slug. Some of the tankless manufacturers are adding small tanks to the unit. 120V 1.5 gallon on some of the minis. recirculation piping and thermostatic mix valves work better after a small tank.

doughpat

It was suggested to me to at least "rough in" a recirculating line to the farthest appliance while the lines are open. Theory being that if the "cold sandwich" or "wait time for hot water" is unacceptable, then a recirculating loop and a storage tank (on the DHW side) would solve that problem. That seems smart to me. I don't really want to spend the extra $ now to install that, since the home is very small and the kitchen faucet only has about 15' of pipe between it and the combi.

The radiant guy insists that a buffer tank on the radiant side is unnecessary. I still don't think I understand why it wouldn't be helpful in reducing cycling of the combi. I think what it comes down to is he is not worried about the Lochinvar turning on and off, while I want to reduce it as much as possible. That being said, I think I might be misunderstanding how the outdoor reset functions and perhaps I need to do some more research on that aspect.

hot_rod

Yes a recirculation loop is sometimes helpful. Keep in mind it will cost $$ to run that loop as it is basically a heating zone Spend some $$ to insulate the hot and recirculation lines to minimize the heat loss.

Timers, thermostats, variable speed circulation, on demand switch, can minimize the cost of running a DHW record loop.

doughpat

Thanks, @hot_rod. I will definitely be going throughout the house and insulating all DHW lines thoroughly.

doughpat

Alrighty everyone -- thank you all for your help with this setup.

I ended up going with a Lochinvar 110, installed by a local radiant specialist (Bend Heating's radiant division). The guy that installed it was a real professional and came from the service side of things so he was very good about adding adequate valves for isolation.

I'll post some pics soon. Still waiting for the plumber to come out and install the potable side (and mixing valve).