Hissing/Sizzling Gordon steam vents RESOLVED with a caveat

StevenNYC

So I’ve tweaked and balanced my steam system pretty well. My last nagging issue was hissing/sizzling vents during cold weather or coming from a set back mostly on my top floor farthest from the boiler rads. I noticed that it mostly occurs right after my vaporstat would cut out at 16oz. I had my cut in at 2oz. I set it that low to minimize short cycling with a goal of 10 mins on.

My theory was that the vents were opening when steam pressure dropped and the vents were still hot while all the steam left as the air rushed into the radiators. This theory led me to think maybe when the pressure built up again, the Gordon’s were passing through a mixture of steam and air which would cause this fizzling sound.

To test my theory, I cranked up my vaporstat to the maximum setting which was around 21oz and cut in to 10oz. Long behold fizzling hissing improved. Caveat, was the delay because of the flue damper. By the time the vaporstat called for heat at 10 oz, the pressure would drop to 5oz before firing up the burners.

So I tried one more trick and flipped the switch on the flue damper to disable it and leave it in the open position. Now the burners came on much sooner and I was cycling between 7 and 21 ounces with a cycle time of about 10 minutes. Hissing/fizzle finally stopped and all rads are nice and quiet now.

How much efficiency am I loosing now? 1-2%? Why would an engineer design the flue to close on pressure and not just thermostat calling for heat or not? Should I leave this be or maybe look at the wiring diagram for a way to rewire the damper to only close when thermostat is not calling for heat? Is it me or are these Gordon vents picky?

mattmia2

You could wire the damper to open on the thermostat instead of the vaporstat

Hap_Hazzard

The standard setup is to close the vent whenever the gas valve cuts out, regardless of where the disconnect occurs. Mine closes whenever the CycleGard shuts down the burners to check the water level, even though it's only for 90 seconds. I've considered rewiring it, but I might replace the CycleGard instead. My pressure never gets high enough for the Pressuretrol to open.

dopey27177

I am happy you found a technical way to resolve an installation problem.

I remember I stated that the hot air or steam temperature was to low to cause the bimetal actuator in the valve to set the pin into the seat and stop the hissing.

21 oz steam pressure = about 218 degrees and 7 oz pressure = about 213 degrees far above the 180 degrees needed to move the valve actuator and seat the pin into the valve set.

Jake

EBEBRATT-Ed

I would try leaving the damper under automatic control and playing with the vaporstat adjustments.

I would suspect you starting to get some vacuum when the steam comes back in the vent is having an issue trying to decide what to do

StevenNYC

@dopey27177

dopey27177 said:

I am happy you found a technical way to resolve an installation problem.

I remember I stated that the hot air or steam temperature was to low to cause the bimetal actuator in the valve to set the pin into the seat and stop the hissing.

21 oz steam pressure = about 218 degrees and 7 oz pressure = about 213 degrees far above the 180 degrees needed to move the valve actuator and seat the pin into the valve set.

Jake

You pointing out the vent closing at 180 degrees in another post, got me thinking. What I’m seeing in my low pressure gauge at the boiler wasn’t necessarily what the pressure/temp was in the radiator. Everything worked great until the system would shut off on pressure. That’s when the sizzling would start happening. So I started thinking that keeping the air out of the radiator between pressure cycles would help solve this issue. Raising the cut in pressure I speculated would do that.

What installation mistake are you thinking was made?

SteamingatMohawk

To what extent is the boiler over or undersized, if at all?

StevenNYC

@EBEBRATT-Ed

EBEBRATT-Ed said:

I would try leaving the damper under automatic control and playing with the vaporstat adjustments.

I would suspect you starting to get some vacuum when the steam comes back in the vent is having an issue trying to decide what to do

I’m not sure whether it was my initial vaporstat settings, the Gordon vent design, or how my system was installed but it seems to have resolved it. I was considering leaving the damper and readjusting the vaporstat but I think rewiring it makes more sense from an “engineering design” perspective.

StevenNYC

@SteamingatMohawk

SteamingatMohawk said:

To what extent is the boiler over or undersized, if at all?

Radiator EDR is at about 290 and boiler is an EG40 rated at 321. It may be a hair oversized, but the real issue is the building is 95 years old. No insulation brick and mortar. You can feel the cold on the exterior walls when it’s real cold out. Most of the time it operates at a fraction of an ounce till temps drop below 30 outside.

mattmia2

It seems like you may have a lot les pickup factor than what is baked in to the boiler rating.

I would just set it up so it is only the gas valve that is cycling on pressure, set the differential so it is at least a few minute cycle and not worry about it. the gas valve and ignition will be happy running a few minute cycles for decades. the vent damper opening and closing like 5 times an hour will mean some day you won't have eat because of that, making it run longer cycles is a great idea but the as valve is much more durable.

StevenNYC

@mattmia2

SteamingatMohawk said:

To what extent is the boiler over or undersized, if at all?

mattmia2 said:

It seems like you may have a lot les pickup factor than what is baked in to the boiler rating.

I would just set it up so it is only the gas valve that is cycling on pressure, set the differential so it is at least a few minute cycle and not worry about it. the gas valve and ignition will be happy running a few minute cycles for decades. the vent damper opening and closing like 5 times an hour will mean some day you won't have eat because of that, making it run longer cycles is a great idea but the as valve is much more durable.

That’s an awesome idea, and real easy to wire. I get the fuel savings of the damper without the abuse on the damper itself during pressure cycling. I also get a more accurate pressure cut in and cutout.

SteamingatMohawk

For an historical perspective, there was a discussion about 10 years ago on HH. Some of the guys are still on HH. The vintage of the article seems to be in the time when some boilers did not have automatic dampers and newer ones do. What changed? I don't know.

https://forum.heatinghelp.com/discussion/143457/should-i-add-a-vent-damper

Personally,I wouldn't mess with Mother Nature. The vent is there for one or more reasons.

Depending on the tightness of the house, draft with the damper open and boiler off can have cooling effects in the room and floor of the rooms above.

Finally, what is the effect if the damper is open and, in the unlikely event, there is a fire in the room where the boiler is located?

What would your homeowner's insurer say about it?

Motorapido

StevenNYC said:

How much efficiency am I loosing now? 1-2%? Why would an engineer design the flue to close on pressure and not just thermostat calling for heat or not? Should I leave this be or maybe look at the wiring diagram for a way to rewire the damper to only close when thermostat is not calling for heat? Is it me or are these Gordon vents picky?

Dunno about measured efficiency gain/loss, but I can tell you from my anecdotal experience, last winter while I was waiting for my replacement flue damper to arrive, I had the broken damper turned off so the flue remained open constantly. When the damper is functioning and closing when the gas is off, my boiler room is about 8 to 10 degrees warmer than when I disable the damper and leave it open. The rest of the basement outside of the boiler room stays a good bit warmer, too (I leave the boiler room door open). So I can't give you a thermodynamics equation, but I can say I sure do keep a lot more heat inside the house when my damper is closed when the flame is off. This brings my mind back to a what-if: What if we all wrapped our boiler jackets like many people wrap water heaters? Seems that the tiny amount of insulation inside the jacket does little good, and you could dramatically decrease standby heat loss by wrapping a blanket of thick insulation around the jacket sides and top. I know, I know, it would look terrible and when a service tech would arrive for periodic maintenance, the tech would think I'm crazy, and the insulation might create a fire hazard, etc. But I've always wondered how much standby loss could be prevented by insulating the jacket.

SteamingatMohawk

I have seen boilers with what is called a draft hood or something similar. The purpose of it is to provide air in the room to mix with combustion air before it passes through the damper and up the chimney. Boilers like this may have a "spill switch". It senses the temperature inside the hood and trips if there is a high temperature, which can be an indication of a restricted path in the duct to or in the chimney. I don't know how common this is.

If your boiler has that function, while putting insulation around the boiler could reduce heat rejected to the room, I believe there may be more heat lost (when the damper is shut) exiting the hood into the room.