Thinking of Changing Boiler Return Protection From 130*F to 140*F?

Hi. I'm thinking of changing out the cartridge on my Caleffi ThermoMix (pellet) boiler protection valve from 130*F to 140*F.

Here's the background. It's a modulating pellet boiler. The tank has a mixing valve around it, so there's no flow to the tank if the boiler return temperature is below 165. Because the baseboard load is a little less than the boiler output, it takes a while for the boiler to eventually come up to temperature when both zones are running. So, the return stays near the minimum temperature of the boiler protection valve for a while.

I am wondering if I will gain anything by swapping out the cartridge to 140*F? I think that a larger percentage of water will be recirculating around the boiler (at 140 mixed return, maybe 150 boiler output). This lesser flow will cause the zone pumps to recirculate around the tank as well (through the tank's mixing valve bypass line). So, there'll be two recirc loops mixing at the zone supply. So, maybe, 150 from the boiler and 135-140 from the zone loop. The quantities of each would change as things heated up, with the recirc around the tank dominating until the boiler heated up past the 140 opening temp of the TheromMix valve.

Does anybody have experience on this kind of experimentation with different return temperatures and its effect on flows?

No.
I recall Bob Rohr changed down to a 115* cartridge on his wood boiler. Most people seem to have 140 on their wood boilers. I figure there's a certain amount of btus available, and whether they're delivered at 140+ at one flow rate or 150+ at a lower flow rate probably is the same. I wonder if there might be some advantage to one or the other.

Creosote buildup is not a problem.

Well, it came in the mail. Hmmmmmm....
Must be someone out there who's experimented with different return temperature.

It's been at 130 so far and I haven't seen any creosote. Now, it's a pellet boiler, and the tank is 100 gallons vs 1000, so it's not running cold like that for a super long time. I'm wondering if there is some advantage to running at a little higher temperature but less flow when there is a load on it would do any good.

Actually, mine doesn't have that capability, but I do have a Ranco aquastat controlling the minimum temperature of boiler pump run. I actually have it at 140 (supply) now. It usually doesn't shut down since the return temperature is 130 minimum.

heaterman said:

I think all Windhagers have what they term a "condensate protection circuit", which should be operating your main boiler pump.

Click to expand...

Not mine.

When both zones are on, it's close, although the boiler does have more oomph than the zones: the boiler temperature gets drawn down pretty good. That's even with the one pipe setup I have, but also have to throw the tank in the equation.

On a different but related subject, I've put a bypass on the tank, so I can control the boiler return temperature: say, for instance, 165, no matter how hot or cold the tank is. This way, the boiler has a tendency to say hot, although when the zones come on, it does still drop considerably, until the mixing valve and boiler brings it back up again. If I would have done the tank bypass in the beginning I wouldn't have done the boiler bypass.