cycle times with a vaporstat

John Lasky

good morning gents.

heating season is almost here.

I want to thank everyone for all the help with my many many gremlins last year. unfortunatly natural gas prices were so high last year, cant wait to see the increase per therm this year $$$$$) it was hard to tell if any of my impovements paid off since the bills were double+ what they were when nothing worked right.

most problems are solved/understood.

I do realize that My boiler is oversized but with de rating according to the factory and Tims advice ("last year")
its only 7% too big according to the connected load.

at the end of last season I installed a vaporstat that has a max range of 16oz.

my question relates to the cycle time ONCE ALL THE DEVICES ARE FULL OF STEAM.

my boiler will run a good 45 mins + when all is cold and will run 25-40 Mins on T stat cycle when maintaining say 67 deg during cold weather.

whats bugging me , I never could get or find an answer about this is the cycle time once the boiler reaches preasure.

once all the rads and baseboards are hot and the boiler reaches the 8 -12 oz setting it cycles on and off "On pressure" untill the T stat is made but the preasure cycles are only 2-4 mins on 2-3 mins off.

is this normal, is this the dreaded short cycling.

my downsatirs is all Burnham baseboards and they seem to lose pressure pretty fast.

but again all devices are good and hot when the presure cycles start.


many thanks have a great day.

"John"

Unknown

That's as good as it gets.

You've reached steam nirvana.

Because the boiler has to be oversized enough to heat everything up from cold, it becomes too big once that happens. If it were still coal, the fire would get banked back and the dampers closed, once the system heated up. You can't do that with oil or gas.

Hence, the cycling.

The cure is to tighten up the house enough to shorten the thermostat "on" cycle enough that it satisfies BEFORE the boiler can reach pressure.

You can let the boiler controls rest, and do their job, now.

Noel

Joe_39

Noel, when it starts too cycle like that

and everything is hot thats steam nirvana..

but when its off for 2-3 mins and then on again, during that off period does all the steam in the pipes condense??

I am curious because I have a gorton #2 and heard that sometimes it stays closed because the vent itself stays hot... If thats the case then on the off and on cycle it would be like having no main vent at all........

wondering if switching to a hoffman main vent would be better????????

Unknown

Not a problem

None of the brands of vent will open during the operation of the vaporstat, as it operates as the high end limit on pressure (low as it is). The "come back on" pressure setpoint is set to the HIGH end of what the system needs to operate and keep the system full of steam.

It doesn't go to zero. Even if it did, and the vent stayed closed,the vacuum formed would HELP the steam move in the next run cycle of the vaporstat. Letting air back in would only cool the radiators where the air ends up.

The vents not opening after the THERMOSTAT satisfies is a different issue.

The whole thing that hasn't been said, here, is this:

If your boiler is going off on pressure, you have been playing with the thermostat setpoint; or, you have a setback thermostat with the setpoint difference set wide; or, you have a house with severe air leaks and it would be hard to heat with ANY type system.

If the thermostat regulates the heat by itself, the boiler will rarely run long enough that the pressure safety limit has to open at all.

Noel

Joe_39

so basically if you set your tstat at 70

and leave it alone for entire winter you really shouldnt have a problem with long on off cycles?

its when you lower to 65 at night and then shoot it back up to 70 is when youre gonna have shut offs on pressure..

correct?

Unknown

yes

precisely

Noel