First, I have been reading these discussions for a few years now and have found the information very valuable!
I have a question about boiler return temperature for a new boiler we had installed last fall, and after parsing the data gathered over the winter wanted to make sure nothing needed tweaked.Some background:
Last fall we had a new gas boiler installed for our radiators in a 1938 2200sqf brick home. We replaced a 140btu boiler with a Slant/Fin Sentinel 105. I had received quotes from 5 different companies at the time and the one we picked was the only one who did a semblance of a heat-loss calculation. (Others wanted to either replace same or even higher since we have a lot of cast iron rads!) Upon further research with the Slant/Fin Heat Loss app, I gather that I'm either sized exactly right or could have even gone with either the Slant Fin Sentry 90 or even the Sentinel 70 if we were to insulate our roof and really button up the house. Observation #1:
Slant/Fin Sentinel 105 worked great all winter, we were never cold. Our thermostat is tied into a home automation server and when I reviewed the logs, I noticed that the Slant/Fin averaged about 45-55 minutes per call for heat. (i.e. Thermostat set at 70, at 68 the call for heat triggers and the boiler would run for 45-55 minutes to bring the temp back to 70.) The old boiler would run for 25-35 minutes on average under similar scenarios. These are the averages for the season (milder days would be less and colder days would be longer.)Observation #2:
The Slant/Fin, after running for 45 minutes would still only show a water temperature of 135 degrees on the HydroStat. (I never monitored the old boiler's temperature, so I can't compare.) On super cold days, the temp might get to 140 after the boiler ran for 90 minutes.Question:
Assuming the behavior in the first observation is correct, I am guessing the reason for the low temperature is because this old house is overloaded with cast iron radiators. That said, If the boiler is only getting to the mid 130's on average, should I be concerned with the cast iron boiler rotting since much of the time it is in the 115-130 range as it heats up? I have read several places that to prolong the boiler life I should be seeing temps in the 140 range.
The boiler has 1 1/4" in/out and the installer put a 1/2" bypass loop in during the install to help keep return temperatures up. I am guessing the bypass loop is not cutting it. Should I look at having the bypass loop converted to include a Danfoss Thermostatic Boiler Protection Valve
to ensure a higher boiler operating temperature?
Sorry for the lengthy post, but I wanted to give a complete picture of the situation. Any thoughts or advice would be most helpful!