Add main vent to radiator valves?

bosJared · December 2018

Hi Everyone!

I'm in a 1920s house with a steam heat system. My condo unit is the first of two, and is on the first floor of a three floor building (a triple decker). The basement is directly below me.

BACKGROUND

The radiators take forever to get warm. Probably 30 minutes - 40 minutes after the system kicks on. My system is a one-pipe system with dry return. The steam main splits into two directions (front of house and back of house), then the dry returns connect to each other in a U shape before dropping into the wet return right by the boiler. There is only one vent (Vent-Rite 35), and it's installed on the U shape of the dry return. There's no way a single vent of that size is efficient for the frankenpipe system that's going on down there.

Since the vent is on the dry return, my understanding is that the steam mains and the dry returns will all fill with steam before radiators get squat. So, I went and insulated the dry returns (they were bare before). I'm also still in the process of insulating the rest of the steam mains around the joints; all straight parts are insulated now. The main in the basement is accessible but it's kind of tight. The lines to each radiator in the basement are right up against the ceiling, between the joists and it is not reasonably possible to reach them.

PLAN

My plan of attack is to do two things in April/May of next year, as the system is working, just inefficient for this winter. First, I want to replace the radiator valves (not air vents - the valves) as they're all a bit leaky. I could probably re-pack them, but I'm hoping to do a second thing simultaneously. I want to add a main vent between the valve and the radiator for each radiator. My thinking is that this will allow the steam to get through all the mains and risers quickest, at which point the radiator valves will do their job and control the steam getting into the radiator.

Is there any issue with adding a main vent between the valve and the radiator?

I'll do all the calculations for how much air needs to be displaced based on pipe size and what size vents will be best when I get closer to doing the actual work, but this system has been driving me a bit batty lately with how best to attack it.

Cheers!

neilc · December 2018

bosJared said:
My system is a one-pipe system with dry return.

just so we're clear,
there is only one pipe to the radiators ?
and a vent on the far side from the supply?

Steamhead · December 2018

There really isn't much air in the typical dry return. You won't lose much heat in the dry returns if you've insulated them. So the existing vent location isn't that bad.

I'd upgrade those main vents first. How long are your steam mains, and what pipe size?

nicholas bonham-carter · December 2018

Don’t replace the steam inlet valves-repack them, or reseat the union faces of the spud if that is the point of leakage.
Enlarge the main vents in their typical location, at the end of the dry return. Start by adding a Big Mouth, and see what difference that makes. Note that your dry return improvements may degrade the performance of any other branch of main serving other apartments. If you do not have the thermostat in your space, you may roast! It would be best to make improvents to the whole system at the same time.
Put a 0-3 psi gauge on to keep the pressure down in the ounces range, and do it this winter, so you can benefit today, and not next year!—NBC

bosJared · December 2018

@neilc Correct, there is one pipe into each radiator. The other side of each radiator has just an air vent. The radiator is slightly tilted towards the one pipe to allow condensate to drain out.

@Steamhead I took some measurements. Coming out of the boiler, there is one steam main. That steam main splits into two legs that we'll call "front" and "back" of house. The Front main is 17' 6" of 2" IPS. There is then 10'0" of slightly smaller pipe (didn't measure that) as a riser to the radiator. Condensate from the Front radiator returns back through the same riser and into a dry return, also about 17'6" of smaller pipe (1" IPS? not sure). The Front dry return joins with the Back dry return near the boiled, before dropping into a wet return / hartford loop / yada yada. OK; second branch. The Back main is 7'2" of 2" IPS before it splits into two radiators ("Bedroom" and "Kitchen"). The Bedroom radiator has 13'6" of riser, the Kitchen radiator has 8'10" of riser. Condensate return then comes back through the risers, into a 7'2" dry return before joining with the Front dry return and dropping into the wet return / hartford loop / yada yada. I have one main vent, on the dry return. Vent-Rite #35.

I don't like that the radiator vents are responsible for venting 10'0" of riser in the Front, and 13'6" / 8'10" of riser in the Back, respectively. There is zero room between the basement ceiling and the risers to add more vents on the risers in the basement; if anything I'd probably have to add them near the radiators.

@nicholas bonham-carter I will take a look at that big mouth vent. I'll take a look at the calculations first to see how much air i'm displacing and what the size of the vents should be. Thanks for pointing me to that vent.

bosJared · December 2018

One other thing I wanted to mention - my system serves only my unit. The other unit in my two-unit building has their own, separate boiler, pipes, etc.

I would love to make all the changes this year - we had some issues just north of me (Lawrence, MA explosions) and all the contractors are pretty slammed. Temperatures are in the ~20 degree range, so I'd rather not do anything that could break the system. My heating bills have been $100/mo or less (I work a lot) since I set it to 58 degrees when I'm at work. I just got a Nest thermostat, so I can turn the heat up as I'm heading home.

This may count as burying the lede... but as far as pressure gauges, my boiler has only a 30 psi gauge, and it never leaves 0 (needle doesn't move at all - trust me, I've spent hours staring at it). I have also never seen the pressuretrol cycle on, so my guess is the pigtail is clogged (best case scenario). Also, one of my radiators is in bad shape (it was covered by a very difficult to remove radiator cover when I moved in; looks like someone tried to fix a crack in the radiator with some plumbing compound). I'm hoping to limp through this season without freezing to death or damaging the system, and then addressing all the items. The amount of money it would take to fix it isn't really an issue, I don't mind spending on maintenance. It's just impossible to find people to do the work right now.

bosJared · December 2018

Sorry for the multiple comments - could someone confirm my logic? I just saw that the Vent-Rite 35 vents about 0.11 CFM; Big Mouth is 3.6 CFM. I have about 25 feet of steam main to vent before the risers at 2" IPS. pi r squared is volume, so about 37.7 cubic inches of air 3.14 cubic feet of air per foot of pipe. That means 25 x 3.14 = 78.5 cubic feet of air in my mains. Round it up to an even 100 cubic feet for the additional air in the returns which are the same length as the mains but smaller, but ignoring the risers because those are vented by radiator vents. That would mean that I need way more venting than the Vent-Rite 35, right?

EDIT: Not sure what I did wrong in the calcs but I just found a sizing chart. .023 cubic feet of air for 2" pipe, per foot. So closer to call it 0.6 or 0.75 cubic feet I need to vent, so the vent-rite 35 at 0.11 cfm should only take 5 minutes or so. The bigger problem will be the risers, which I need to measure the pipe diameter on still.

KC_Jones · December 2018

5 minutes believe it or not is an eternity. You want the big mouth vent for 25' of piping. For a similar length of main I can get steam to the end of main, starting from burner firing, in 3 minutes. Actual steam travel time is probably 2 minutes or less.

nicholas bonham-carter · December 2018

I wouldn't spend a lot of effort on measuring the pipes of such a relatively small system, when there is the Big Mouth "game changer" vent available. In days gone by, when there were only Gortons, and Hoffmans to choose from, it was necessary to do some calculations to determine how many to order.
Remember, the aim is to balance the low restriction of the main venting, with the slightly higher cumulative restriction of the radiator vents. this will fill your nicely insulated mains first, and then all the radiators subsequently.
Just order one, or two, with a low pressure gauge, and put them on. Changing the vents will a reasonably easy DIY job, and the low pressure gauge a bit more challenging. Your gas company may not thank you for using less gas, but the comfort will increase.--NBC

Fred · December 2018

@bosJared , BTW, you would not vent a riser in the basement. It would just close when steam from the main hit it. If a riser is vented, it needs to be at the top of the riser, whatever floor that may be.

Chris_L · December 2018

Post a picture of where your dry returns drop down to the wet return. If they are connected above the water line, as I think you said, that should be fixed. They should tie together below the water line.

In any case, you'll get some good advice about where to put your main vents.

You shouldn't need to mess around with venting the risers or the radiator valves if you can put some good vents on the dry returns.

Add main vent to radiator valves?

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