Best settings for Vitotrol and a prog. thermostat?

CMadatMe

There's the pressure drop across the HX, you tell me the right speed? It's 3....

sunlight33

Isn't that assuming the boiler is working 100% at 114,000 Bth/h? What if the boiler is only working at 40% of that?

GW

The flow is a constant, it's a fixed speed pump. It's kinda confusing if you let it be. The boiler is looking to make a certain temp. So if you're at 40%, your boiler is seeing 40% of its total capacity for a load. Get it, or no?

So, if you're plugging along at 40%, let's pretend you open all your windows for some nice fresh air. Your heat flys out and cold flys in, dropping to the floor. Your heat emitters will now shed its BTU's faster right? Now the boiler will Rev up becasue the return temps are lower.

So, lower return temp means a larger hill to climb, the boiler will start working harder.

sunlight33

Thank you Chris and GW for the clarification.

sunlight33

Is it true that mod-con running on propane can condense roughly 10 degrees higher than running on nat gas?

CMadatMe

Condensing is all about the dew point, ie CO2...

sunlight33

I see, take 10% CO2 from propane vs. 8.5% from methane. That's like 131F vs. 123F according to the graph.

sunlight33

Last night the temperature got as low as -9F, and the boiler still cycled on/off about 1.5 to 2 times an hour (very similar to when the temperature was in the 20's), any thoughts on that? I am curious as to why the boiler wouldn't just modulate lower and burn at a longer interval.

CMadatMe

The bottom end of the modulation rate is what it is and if the system side isn't putting demand on the boiler then why would it go into higher fire? Two cycles in an hour at -9 for seems really good. Boiler wants to coast not peddle to the metal. I noticed you didn't say the house was cold.