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Steam Radiator Vents/Actuators

We purchased a 1900 Victorian 3 story office building heated by single pipe steam system. The boiler is a 2005 Dunkirk and seems to work fine. The thermostat is programmed to set at 70 for 5 a.m. I've done a questionnaire to all tenants and it sounds like in past years the 2nd floor offices are usually chilly in the morning except if it's very cold outside, then it is warm. They used space heaters often. The 1st floor offices in general don't seem to have this problem. The thermostat is in a common hallway on the 1st floor which to me must be the primary cause for this and intend to move it up to the second floor in common hallway. All radiators have air vents with thermostatic actuators mounted close to middle of radiator opposite end of the steam inlet. Inlet valves are open all the way. I expect once I move the thermostat, the 1st floor offices will be too hot. My questionnaire also asks if they ever adjust the actuators and if so, do they notice a difference but have never had anybody say they noticed a change. This weekend, I will be doing a lot of experimentation. My questions are: Should I expect actuators to make much difference in controlling each radiator temp? I'm sure vents/actuators can go bad, but I've read that it is pretty unusual, what is your opinion? I actually live 2000 miles away and so making the building "Smart" as possible is my goal. I have thought that these actuators are "TRV's" and I see "Smart" TRV's but could not find any application online that they used them for vents, only radiator water valves. Are actuators actually TRV's and could I use a Smart TRV? And could I pair a thermostat to that TRV? I saw a comment where a guy said Smart Thermostats (for the boiler) don't work well with steam boilers. Why would that matter? The previous owner used the supposedly most reputable and largest HVAC company in town so I wonder why the heat is so messed up, especially the thermostat location. I'm meeting a professional steam boiler guy so we can go through the whole system, but I wouldn't be surprised if he wasn't up on the smart stuff. Thanks in advance for your help, much appreciated.


  • mattmia2
    mattmia2 Member Posts: 8,434
    If the second floor is also the top floor it has the roof so it has a lot more heat loss than the first floor. If the areas are more or less separated the thermostat isn't going to see that load.

    TRVs on a steam radiator can only keep the radiator from heating at the start of the cycle, it prevents the air from venting and letting the steam in. Once the radiator is full of steam it will keep heating until the boiler shuts off and it stops supplying it with steam so the steam condenses and it fills with air again from the vent. This means that in order for the TRVs to work the boiler needs to cycle on and off and the users need to understand that turning down a TRV won't be instant. The lower floor may still overheat but dialing in the TRVs will help.

    The first step is to put faster venting on the upper floor radiators and slower venting on the lower floor radiators so the upper floor radiators heat faster and the system is better balanced without the TRVs. I would try this before moving the thermostat.
  • Jamie Hall
    Jamie Hall Member Posts: 21,541
    There are specific TRVs to be used for steam radiator vents -- and they are quite different from the TRVs used for hot water. I'm not aware of any smart steam TRVs, though there may be some.

    The best way to go after a problem of this sort is multi-step, and with you being so far away this could be a problem.

    The first step, of course, is thermostat location -- and you seem to be on that.

    The second is the hard one: select or adjust the radiator vents so that the heat is even, or as even as it can be, in all the spaces with the boiler going normally. You may find that some radiators just heat too slowly; if so it is likely that you may also need additional (or some!) main venting.

    Only then, with even heat, can you start contemplating TRVs -- and when you do, keep in mind that as @mattmia2 implied, they can only reduce the heat from a given radiator, not increase it -- and they can only do that at the beginning of a steam cycle.

    As to temperature settings, steam doesn't play well with larger setbacks such as overnight. A few degrees, OK. Perhaps 5. Much more than that and recovery just takes too long.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • OnePipeSteamer
    OnePipeSteamer Member Posts: 7
    edited September 2022
    Thanks for your feedback. I'm going there tomorrow for about 3 weeks to do maintenance stuff. I have a lot of construction experience but never dealt with steam heating systems. There is a 3rd floor which is an apartment which of course has issues too but the guy likes it on the cool side so I'll tackle that later. Attached is a picture of the typical setup. I see an actuator online that looks like this one, but it says for water and 2 pipe steam. I think I'll go with you guys and kind of start from scratch. Should I to get it balanced first, then re-evaluate and go from there including moving the thermostat if necessary or should I just go ahead and move the thermostat first. I think I get about what you guys are saying about the trv only affecting the beginning of the cycle. Once the air is out, it serves no purpose, kind of.
    EBEBRATT-Ed Member Posts: 13,813
    Trvs can only limit the heat, not give you more heat.

    Operate the boiler with the thermostat (moving it may or may not help) and keep the pressure control on the boiler set for 2psi burner cut off (maximum) the lower the better. Make sure any main vents in the basement are working and updated.

    Then try and balance the system as good as you can. Fine tune with the TRVs.

    You may want to get some new TRVs for spare and keep them in the boiler room.
  • random12345
    random12345 Member Posts: 469
    edited September 2022
    This is the booklet to read on venting: https://heatinghelp.com/assets/documents/Balancing-Steam-Systems-Using-a-Vent-Capacity-Chart-1.pdf Steam has to push the air in the steam mains out the main vents first before it can start to push out the air in the pipes coming off the mains (aka "runouts") to the individual rads. In order to balance the system, that booklet will show you how to calculate the air volume of all those pipes and radiators so you can determine what size main vents and radiator vents you need. Steam follows the path of least resistance. And that resistance is determined by how quickly the air is being pushed out of the respective vents. Insufficient main venting could be a problem for you here. All else equal, when the resistance is the same everywhere, the runouts closest to the boiler will fill first. Maid o mist makes cheap radiator vents with a set of removable orifices that make experimentation/adjustment easy. Can you post some pictures of the boiler, steam piping, and main vents?
  • mattmia2
    mattmia2 Member Posts: 8,434
    Now knowing that the second floor is not below unheated attic, it sounds like most of your problem is with balance rather than different loads. Since there is more runout to the radiators on the second floor they should have somewhat faster vents to heat at the same time as the radiators on the first floor and i'm betting someone put the same vent on everything when they installed the TRVs regardless of radiator size or distance from main.
  • OnePipeSteamer
    OnePipeSteamer Member Posts: 7
    Thanks all for the feedback and help, greatly appreciated. I don't have pictures of the system just yet, but will get some this weekend. Thanks for the study link, will make good reading on the flight.
  • OnePipeSteamer
    OnePipeSteamer Member Posts: 7
    I finally made it back to the office building and noticed the main air vent was spewing steam. I had a steam service guy come over and he agreed, that's not right. Put on a new one it works fine so now to balancing. I've also replaced the old thermostat on the 1st floor with smart thermostat plus remote sensor on 2nd floor. I am getting plenty of heat upstairs now and it appears I will be able to control 1st floor rooms with actuators. I started digging into the "Lost art of steam heating". Lots of info there. It explains how to estimated PSI required to get steam to farthest point. Farthest point is 61 ft, then factored in turns, fittings, and pressure drop and came up with needing a cut-in of .29 psi. I read that the least you can go is .5 psi. So I want to try .5 cut-in and and cut-out of 1.5 psi. The book suggests 1 lb differential. See the pic of the pressuretrol and it's current setting. It has a cut-out of 3 psi but looks to me like the cut-in is about 2lb 4oz. For what I want to do, I would need to set the main to 1.5 and the Diff to 4. How does that sound? Another steam guy online said in his experience the vent actuators work better at 2 psi or less.
  • neilc
    neilc Member Posts: 2,230
    so drop the main down to 1, for a 1 psi cut out,
    and raise the diff to 8 oz, and the boiler will cut back in at 0.5 psi

    has the pigtail been checked and cleaned for free breathing ?
    are you able to easily blow back into the boiler after clearing the trapped condensate?
    known to beat dead horses
  • OnePipeSteamer
    OnePipeSteamer Member Posts: 7
    Ok, I'll try that. I don't know when pigtail was checked last, but I will. Thanks.
  • mattmia2
    mattmia2 Member Posts: 8,434
    That vaporstat is the better control for a steam system yours is just set way too high. The fact that it is a vaporstat says that someone that knew what they were doing was involved at some point.
  • OnePipeSteamer
    OnePipeSteamer Member Posts: 7
    Thanks for your comment. Dan Holohan in his book said "A Vaporstat is the nicest gift you can give a house-heating steam system." The previous company that maintained (and maybe installed the boiler in 2005) the system is very reputable, but when I bought the building and asked for them to come over and educate me on the system, they said, sure in 2 months. I called another and someone was here in 4 days and spent 2 hours with me. Also, I know the previous owner knew nothing about the system and didn't like spending money on the place. I'm thinking, I'm going to be able to reduce heating costs quite a bit and the tenants will be warm.