H2O Priority

Parachute

I'm curious whether any of you pros have a best practices for choosing or not choosing indirect water heating priority. All things being equal (i.e., there's more than enough boiler capacity to run space heating and water at the same time) is there any preference? I raise the question because on my Prestige Solo boiler the highest the boiler will fire for H20 is 150 degrees, while space heating is 194. I've played with priority and non-priority and it doesn't seem to have a significant impact on how quickly the water heats but can adversely affect space heating because the boiler is only firing to 150 when there is a call for heat not some higher number that a call for space heating might warrant.

Zman

I like DHW priority. I usually am running a much lower temp for the heating side so it makes sense to have the DHW separate.

The DHW priority temp is determined by the DHW add setting in the boiler.

I do have to ask why you are running the heat so hot with a condensing boiler? It is a pretty rare system that needs more than 180 on design day. With outdoor reset, you could run in condensing mode (<140 supply) at least part of the time and gain efficiency.

Parachute

Zman. I was just giving the manufacturer's upper limit for H2O and space heating. I don't run it that hot at all. But on a cold day like today, the outdoor reset will have the boiler running at 160 or so for space heating but when there's a call for H20 that drops to 150. It works, but it seems it would be more efficient just to pass the 160 water to the heater until the H2O switch indicates the call is satisfied rather than having the boiler modulate down to 150 and then work extra hard to get back up to space heating temps.

Zman

I guess it is a horse a piece if the boiler is oversized and the operating temps are similar.
I like it because it guarantees adequate hot water and allows you to push he envelope on the reset curve without worrying about the DHW.
I am used to heating curves that start at 120 and go down from there.

SWEI

Has your ODR curve ever been properly tuned?

Parachute

Not an oversized boiler issue. I finally found the setting to raise the H2O setpoint temp.