Boiler cycles vs hours of operation

FranklinD

I have a question regarding cycles vs total on-time. My Burnham ESC has a cycle counter and total runtime meter. I checked it yesterday for curiosity's sake. It showed 131 cycles and 32 hours (this is the amount for this year only, started counting when the boiler was first used September 26th -- roughly our first frost this year). I know there were a few instances involving my kids where the stat got turned up and turned right back down again.

I'm just curious what the 'optimal' cycle rate is...I know this works out to an average of 14 minutes per cycle, and I understand it's going to be different at any given outdoor temp. It's been in the low 30's at night the last 2 weeks, topping out around 50-52 during the day. We use about a 3 degree setback at night and durin the day. I should say, it's always set at 66, except from 3:30-8pm when we're all home, at which time we set it at 69.

This house has cast iron radiators. The original boiler was rated at 155k (input) and this replacement is rated at 91k input...based on a heat loss survey.

Searching online, I've found instances where people say their ESC is cycling the burner on/off every 2-3 minutes and that's the way it should be...to me that's just too much. I do have a boiler
Bypass, and can adjust the valve so that it zooms up to hi limit and shuts off the burner...but then it takes forever to heat the system water. Or I can go the other way and adjust it so that the boiler hits the 140-150 area and heats pretty well...but never reaches the limit at all. Is there a sweet spot there? I've always wondered that.

Sorry for the wandering question. This stuff is so interesting to me, and my family is tired of hearing about the 'discoveries' I'm making as I research all this stuff. They don't care, as long as the house is warm.

Thanks folks!

Zman

The industry has more or less defined short cycling as more that 6 cycles per hour.
By that standard you are doing pretty well.
In a perfect world, the boiler would modulate to the point where it matches the load perfectly all the time.
Any boiler runs at peak efficiency during the steady state part of the cycle. They are much less efficient at the beginning and end.
There are also the issues of wear and tear on the controls and condensate damage to the boiler and vent.
It sounds like you have a pretty good balance with yours

Carl

Ironman

Another thing to understand about cycling is that for the most part it's out of your hands. Coming out of setback will produce a long cycle, but much of it depends upon boiler sizing, zoning, how it's controlled, type of emitters, system mass, etc.
It looks like like yours may have been sized right if the load calc was accurate. Sadly, this is all too often not the norm.

FranklinD

Thank you for the comments. I think I have it about as good as can be...it warms up above 140 relatively quickly, but this early in the season system temp is still very low...90-110* for the most part.

Will be interesting to see how it behaves once the temp drops to our usual winter levels. Last winter we had 66 consecutive days with a high of zero or below iirc. It was a rough one...had the highest gas bill I've ever had in this house (but with the old boiler).

Thanks again!

Rich_49

Do you have any way to determine the return water temp at the boiler ? There is much more help if your supply and return differential can be fine tuned . Using the energy the boiler provided and getting the most work out of it is a big benefit .