Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Did my vapostat do this?

johncharles Member Posts: 50
edited December 2022 in Strictly Steam
In 2019 we had an overnight low of -20. My steam boiler kept us warm with the longest cycle time being a noisy 45 minutes. 

By that time the gortons would be howling and the pressurtol was actually turning the boiler off.

Based no that experience I installed a vapostat. We’ve had some cold nights but nothing quite comfortable to 2019 until last night. 

Last night was a much quieter affair, and again the house was comfortable and warm but I noticed that the system performed differently when I reviewed my ecobee logs. 

Instead of the longest cycle being 45 minutes the call for heat went continuous around 4 am the house stayed 0.3 degrees below set point for the entire time and I did end up waking up over the night around that time.

When I went down to the basement the boiler was running for about 3-5 minutes and then the vapostat would shut it off for the amount of time it took the damper to rotate 180 from open to cloed and immediately back to open. 

This carried on the entire night, the radiators were fully heated the vents were quiet. And the house stayed comfortable. 

My question is this in 2019 we had a low of -20 and the boilers max runtime was only 45 minutes last night we had a low of -9 but the boiler reached a point where it ran for 4 hours non stop. Is this all because of the vapostat? Which is the only charge to the system since then?



  • bburd
    bburd Member Posts: 869
    edited December 2022
    The difference is probably due to the wind. The infiltration portion of the heating load can vary considerably with   wind speed and direction. If your fuel is gas you may also have experienced lower gas pressure, leading to longer burner run times. This sometimes happens in very cold weather.

  • BobC
    BobC Member Posts: 5,470
    Gas utilities sometime add compressed air to the supply to keep pressure up on very cold nights. This reduces the BTU content so boilers have to run longer to keep the temperature up.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • ratio
    ratio Member Posts: 3,600
    If the radiators were entirely filled with steam, then we know a few things. One, the installed radiation is pretty well matched to the heat loss (which includes infiltration losses), since we sagged less than one degree with a continuous call. Two, the boiler is somewhere oversized for the installed radiation, since we were cycling on pressure at maybe 4:1 on. The radiators would have been putting out slightly more heat in '19 because higher pressure steam is hotter, but I'm not sure how significant that difference is.
  • mattmia2
    mattmia2 Member Posts: 9,391
    Vicks vapostat.

    You could increase the differential a bit to lengthen the cycle to compensate for the vent damper or maybe increase the pressure a little if it is no longer steaming by the time the burner fires again.

    I wonder if it would make more sense to open the vent damper off the thermostat rather than the call to fire the burner(obviously keep the vent proving in the safety chain) to reduce wear on the damper and reduce the time to start a call to the burner.

    I think it is probably mostly the wind, in mi it has been very windy since Thursday night. The vent damper reducing the amount of time the burner is firing is also a factor.