Hours a day a normal boiler runs??

mike parnell

Just wondering how long on a typical installation ,the average boiler will run?? I have installed a clock on the burner wiring and it has been lees than two hours a day. I'm in Hopkinton Ma. Its been cold here lately,just thinking that I did a good job installing this system,P/ S  ,six zones radiant in the floors,3000 sf house, I learned alot at Heating Help .Com... Thank You all..............Mike in Hopkinton

Jean-David Beyer

how long the average boiler will run?

Note that I am a homeowner, not a contractor. I do not know average, but I am learning about my system. This is the first year I have had it.



I do not know if a mod/con boiler with outdoor reset is typical or not. I have downstairs heated by radiant slab on grade. Upstairs is heated by Slant/Fin baseboard, and I have more of that up there than would be necessary if I put 180F water in it (14 feet in each of the two rooms). I had excess installed so I could run at lower temperatures to increase condensing.



I read that one should adjust the outdoor reset so that the circulator runs all the time, and that the outdoor reset is adjusted to control the house temperature so that the thermostat is just short of being satisfied all the time. I do not know if that is really the most efficient way to run the system, but it should be close if the cost of running the Taco 007 IFC circulators is not too high. About 85 watts each, IIRC.



I cannot manage that, but I come quite close downstairs. If the thermostat calls for heat and the temperature outdoors is 60F or higher, I put 71F water into the slab. If it is colder than that, the reset curve goes up to 120F at -1F outside. On one very cold day, the thermostat indicated it was satisfied, but it was not; it was extemely close. It ran all 24 hours that day. On a very hot day (for winter: perhaps 50F outdoors), the boiler did not run at all for downstairs. Most days it runs 8 to 16 hours. Yesterday it ran 12 hours 17 minutes. This was for downstairs.



For upstairs, it does not run very much because at 0F outdoors I need only 6500 BTU/hr and 97.5% of the time it does not go below 14F here in NJ. So far this winter it got down to 13.6F once, and it is usually between 20F and 30F it seems to me. Upstairs I put 110F water into the baseboard when it is 60F or above outdoors, and it slopes up to 135F at 6F outdoors. I picked 110F as the minimum, because any less and there is so little temperature drop that the boiler cycles too frequently. The mod/con can not get below 16,000 BTU/hr by modulating, so it has to go on-off mode below that.



All these numbers are my current values. This is my first winter with the system, so this may not be the final values. I imagine they are pretty close, though. I wish we would get a few very cold days, though, to check that end of the curves.

Unknown

Boiler size and controls matter

Most boilers are cast iron antiques and do not have the benefit of outdoor reset (standard on all viable ModCon boilers today).

Controls known technically as Bang-Bang (on/off) work to simply switch burner- and most often circulators- on and off all at once. Conventional boilers operate until the call for heat (thermostat) is satisfied or they reach their high limit, which ever comes first. Outdoor reset can help, but minimum water temperature must be maintained in low efficiency boilers.

In design conditions (the coldest few days of the year in your area) the boiler should theoretically operate 24/7. By habit and tradition nearly all boilers are grossly over-sized (more than 10%) for the load they serve, which means they will turn off at a rate directly related to amount of excess output they have. When significantly over-sized, boilers will cycle on and off too frequently (short cycle) negatively effecting operating efficiency, reliability and comfort.

As the heating system needs the hottest water on these precious few days, it will cycle more for the majority of the heating season. Radiation can effect cycle time of course, fin tube being the worst and cast iron being the best at stretching cycle time.

The incomparable ModCon or modulating condensing boiler, if properly sized will as JD says run nearly all the time improving operating efficiency and comfort at once.