Thermostat shuts down before radiators are completely hot.

WilliamBendick

I have a Burnham MegaSteam boiler and a Honeywell CT8602 thermostsat. I have the thermostat set to 69 degrees around the clock, 7 days a week. The problem is that when the thermostat calls for heat the steam comes up but the thermostat shuts down before the radiators are completely hot. The room temperature display on the thermostat stays at 69 degrees all the time. The radiators furthest from the boiler get less hot. Any suggestions?

acwagner

Are the rooms cold or uncomfortable?

Is this a single pipe or two pipe steam system?

It's likely a balance problem, or your thermostat is not set for steam, or both. On page 11 of the thermostat manual it says how to set it for steam. Should be set to "1 = Gravity or steam system". I believe the default setting is 6.

WilliamBendick

Here's my reply:
The rooms furthest from the boiler are a little colder. It's a 1-pipe steam system. The thermostat is set to "1=gravity or steam system".

ChrisJ

WilliamBendick said:

I have a Burnham MegaSteam boiler and a Honeywell CT8602 thermostsat. I have the thermostat set to 69 degrees around the clock, 7 days a week. The problem is that when the thermostat calls for heat the steam comes up but the thermostat shuts down before the radiators are completely hot. The room temperature display on the thermostat stays at 69 degrees all the time. The radiators furthest from the boiler get less hot. Any suggestions?

I suppose whether or not you have a problem depends on what you're trying to do.

Are you trying to keep the rooms comfortable?
Or are you trying to fully heat radiators for some reason?

If the radiators further away aren't keeping those rooms warm enough then we have some work to do.

WilliamBendick

The rooms furthest from the boiler are a little colder with the radiators only getting a little bit hot. Also, when the outside temperature gets very cold, say below 20 degrees the problem goes away and all the radiators are getting hot.

WilliamBendick

I also have Hoffman 1A adjustable air valves on all the radiators with the ones furthest from the boiler set fastest.

Jamie Hall

I don't think you have a problem -- unless you want to get those further rooms a little warmer. What you are seeing is pretty typical behavior for a heating system.

acwagner

If the colder rooms are too cold for your tastes then you'll need to adjust your venting strategy. Either increasing the venting on the cold room radiators or slowing down the warmer rooms radiators. Or doing both. It takes some trial and error, and also time to see the effects.

Also, the system will respond differently depending on how often it runs. Colder outside temperature typically means it runs more often, and the pipes will be warmer between cycles. Warmer outside temps means the opposite. Which is why when it's below 20 degree all the rads heat up fully but don't when it's warmer.

I generally do balancing when the outside temp is a "typical" winter day, and accept that it will be slightly off when outside temperatures are either warmer or colder.

What kind and how many main vents do you have?

WilliamBendick

I have 2 main vents. I 'll have to check what brand they are.

Mike Cascio

Also are your steam mains insulated? If they are not, the steam will get quite weak at the end, especially in the shoulder seasons.

Fred

Sounds pretty typical to me. Radiators won't necessarily get hot all the way across when outside temps are milder. They may not get fully hot even on those 20 or below days, depending on how large they are and how much heat is needed to bring the house up to temp. You may try slowing down the vent on the radiator, in the room that has the thermostat, maybe one setting at a time to slow steam to that room, until you are happy with all the rooms.

WilliamBendick

Well, I'm thinking about replacing my Honeywell thermostat with a thermostat that has an adjustable swing like the Lux TX500U. It's swing is adjustable from .25 degrees to 2.25 degrees. Any thoughts on this?

Jamie Hall

WilliamBendick said:

Well, I'm thinking about replacing my Honeywell thermostat with a thermostat that has an adjustable swing like the Lux TX500U. It's swing is adjustable from .25 degrees to 2.25 degrees. Any thoughts on this?

Uh... why? Adjusting it for a wider swing will help get all the radiators hot, if that is the objective -- but it's not. The objective (at least usually) is to get all the rooms comfortable at the same time, and a wider swing won't do that. All it will do is let the temperature drop farther in the room with the thermostat before the system fires up. It will do nothing at all to help with a balance problem, which is what you have (if indeed you have a problem at all -- as some have mentioned).

Bio

Sounds like your main vent isn’t big enough, and steam is favoring the radiators closer to the boiler, you want to fill the mains first then the radiators

WilliamBendick

I checked on the two main air valves in the cellar. They are Hoffman 4A valves.

KC_Jones

WilliamBendick said:

I checked on the two main air valves in the cellar. They are Hoffman 4A valves.

Unless your mains are 5-6' long that isn't nearly enough venting and is most likely the source of our problems. Once you upgrade the main venting things will get better, but you will most likely have to balance your radiators all over as those vents are currently doing some of the work of the main vents.

How long and what size are your mains? With that information we could recommend the amount of main venting you need.

Pictures of your current vents would help as well.

WilliamBendick

Here's a picture of the Hoffman 4A main air valve.

ChrisJ

We don't need a picture of a 4a. We know what that is.

We need pictures of the boiler, piping around it and where the vents are.

WilliamBendick

I have attached a picture of my boiler and piping.

Both mains are 2-inch pipe with an O.D. 0f 2.375 inches. I measured both mains from the boiler to the location of the vent. The Front Main measures 383 inches, and the Rear Main measures 548 inches. I calculated the volume of air each vent holds. For the Front Main the volume is .73408 cu. ft., and for the Rear Main the volume is 1.05033 cu. ft. The main air vents that are currently in place are Hoffman 4A vents. Should these vents be changed?

KC_Jones

I would suggest for the shorter main you need a single Gorton #2 vent and for the longer main quantity 2 Gorton #2 vents.

The Gortons vent at roughly 8 times the rate of those Hoffman vents, this should make a dramatic difference in system performance.

You will might need to balance your radiator vents after this change, but this is the process for balance, mains first rads second.

ethicalpaul

That's very nice near boiler piping!

WilliamBendick

For the longer main, would using one Barnes and Jones Big Mouth vent instead of the two Gorton #2 vents be OK?

KC_Jones

WilliamBendick said:

For the longer main, would using one Barnes and Jones Big Mouth vent instead of the two Gorton #2 vents be OK?

It sure would.