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I replaced a 34 yr old boiler with a new one. The new one was sized down based on EDR calculation of the various radiators; total of 10, mostly Sunrads. The new boiler's output is rated at 281MBTU/hr while the old boiler's rated output was 320MBTU/hr. The system has two loops. A shorter 24' loop that feeds all the radiators on the back of my 3 story house. The second loop is about 40' and traverses an unheated crawl space and feeds all the radiators in front of the house. Both mains are 2" pipes, the returns are 1.25" and the risers are 1". All fiberglass insulated.
The system had NO main vents. The installer figured if the old boiler did not short cycle and was heating all the radiators except the last one in the front loop, he could heat everything evenly by adjusting vent sizes on the rads. Since the system was installed in Sept. everything worked fine after extensive skimming. Nevertheless, I had another boiler man look at the system and he installed 2X Gorton #1on the shorter loop and one Gorton #2 on the longer loop on antlers. The stat, a Nest set for "True Radiation" to 67 degrees at night and 70 degrees during the day.
By December temp in New York City area dropped and everything changed!
When the boiler starts up in the morning, it runs for 40mins(a little longer on colder nights) and shuts down(not on pressure). The temp rises to 68. After that the boiler cycles every 3 mins (3 mins on 1.5 mins off) on pressure and takes 2.25 hrs to reach 70 degrees. The cut-in is 0.5PSI and the cut-out is 1.7PSI on a 0-5PSI gauge. After hitting 70 degrees, on most days the stat calls for heat 1/hr and the boiler runs for 15mins and shuts down on temp. The house is reasonably well insulated. Vents do not spit but expel air for a long time and produce a low gurgling sound. I have uploaded some pictures of the system.
One of the two Gorton #1 vents on the shorter loop failed to close and has been replaced with a B&J vari vent. The #2 on the longer loop is functioning properly. The third floor is generally 2 degrees lower than the first two floors
There isn't a significant change in my heating costs based on graphs of current month's gas usage vs last year for same month on ConEd bills.
Can anyone suggest ways to limit/correct the short cycling? Thanks in advance!