3/8" radiator vents?

snootyusher

I moved into a new apartment in a 6 floor/24 unit building and getting some beneath-the-floor knocking now that the heat has turned on. Figured first thing I'd do - after cleaning out the radiator's air vent with vinegar to no good results - would be to replace the vent.

It's a strange Honeywell 3/8" adjustable model with a separate removable air vent. (I only vinegar'ed the removable vent part).




Since that hasn't resulted in success, I figured I'd replace the whole thing. So I started researching and found that 3/8" isn't really a common size at all, and I can't even find this Honeywell model at all. I removed it and measured the radiator's opening for the vent and confirmed it is 3/8"

You can see on the vent itself, it's labeled 3/8"



Looking to see if anyone can offer a bit of guidance here on how to proceed

Thanks

EBEBRATT-Ed

What you have is a TRV...."Thermostatic Radiator Valve"

A TRV acts as a thermostat to prevent a room from overheating.......they will not give you more heat if the boiler is off. They are usually used in the rooms that tend to overheat.

If your getting banging try turning the thermostat knob to a lower setting....venting too fast may cause banging.

If that doesn't work, put a level on the radiator and make sure the end with the TRV is higher than the end with the pipe. A 2x4 and some blocks to pry with and some shims of wood or metal to raise the trv end may help

mattmia2

Does that particular TRV have a way to let air in when it is closed to let the radiator drain after the boiler shuts off?

Is the supply valve on the other end of the radiator all the way open?

snootyusher

re: knob setting; I've got it set quite low
re: level; it seems tipped towards the pipe sufficiently
re: venting/letting air in...part of why I chose to clean it out with a vinegar soak was because I never actually heard any of (in my experience) the typical "hiss" of air being pushed out as the radiator heated up. any thoughts on that?
re: supply valve - yep, fully open

By the way, the other steam system elements in this room are a vertical pipe coming out of the floor + into the ceiling without a vent; and what looks like a capped-off outlet for presumably a second radiator that is no longer here:





thank you!

gfrbrookline

That is a Honeywell TRV, no vacuum breaker. That might be part of your problem as @mattmia2 was suggesting.

gfrbrookline

Judging by the break in the trim and shadow line there was a wall removed next to the steam pipe. The capped off pipe would have been for a radiator in the other room.

If the system is dialed in correctly, doubtful, you shouldn't really hear hissing. Does the radiator provide enough heat? I know you mentioned banging, do you also hear gurgling or boiling sounds?

snootyusher

Nope, no other sounds and the heating does seem sufficient.

So regarding what you say about a vacuum breaker, and my search finding limited 3/8" air vents, how do you think I should proceed?

Thank you

gfrbrookline

Can you post a pic of the radiator?

snootyusher

Here you go (hit send too fast, next post has photo)

snootyusher

gfrbrookline

Replace the TRV with a Gorton 5 and send the landlord the bill.

https://www.supplyhouse.com/Gorton-G5A-Gorton-No-5-Angle-Vapor-Equalizing-Valve-3528000-p

The TRV is making your radiator retain water since it lacks a vacuum breaker which is likely causing your knocking sound. Steam is coming up and hitting the condensed steam and they are fighting one another.

snootyusher

I'd happily do that, but it says 1/8" and the hole (and current TRV) is 3/8". Wouldn't that be incompatible?

gfrbrookline

If you look closely you will see a 3/8 nut attached to a 1/8 nipple going into the radiator. Loosen the nut, detach the TRV and it will reveal the nipple. You will need an allen wrench to get the nipple out of the radiator. I don't remember the size of the wrench required.

That is a small radiator, you might want a Ventrite No. 1 vent so you can adjust it slightly.

snootyusher

These are the two states of disassembly I seem to be able to manage easily. Are either of these what you're describing or have I missed the mark? Thanks

gfrbrookline

You got this one, now replace it with a conventional properly sized vent and you should be good to go.

snootyusher

gfrbrookline said:

You got this one, now replace it with a conventional properly sized vent and you should be good to go.

Thank you! And just so I fully understand before purchasing the Vent-Rite #1...I should install the 1/8" conventional sized vent directly into the 3/8" hole in the radiator like in the 2nd photo - and essentially toss the nipple/TRV that I fully removed?

gfrbrookline

The hole in the radiator is 1/8", the nut adapter assembly to put it in english was a 3/8" union. You can now use any conventional vent on the radiator.

gfrbrookline

The first time I removed one of these I was scratching my head because I thought it was a simple twist and play like every other device. Honeywell over thought the connection but forgot the vacuum breaker to make it work correctly.

snootyusher

gfrbrookline said:

The hole in the radiator is 1/8", the nut adapter assembly to put it in english was a 3/8" union. You can now use any conventional vent on the radiator.

maybe I'm thinking about this the wrong way but here's a photo of the hole with my tape measure showing 3/8

KC_Jones

gfrbrookline said:The TRV is making your radiator retain water since it lacks a vacuum breaker which is likely causing your knocking sound.

This statement is factually incorrect.  The only way it can prevent water from leaving the radiator is if the supply pipe/valve are completely full of water.  Since the condensing steam is just a trickle at the bottom of the pipe it will freely drain regardless of the presence of a vacuum breaker.

The function of the vacuum breaker is so that when the TRV closes the vacuum can be broken to prevent additional steam from entering and the radiator continuing to heat when one does not want it to.

snootyusher

KC_Jones said:

gfrbrookline said:The TRV is making your radiator retain water since it lacks a vacuum breaker which is likely causing your knocking sound.

This statement is factually incorrect.  The only way it can prevent water from leaving the radiator is if the supply pipe/valve are completely full of water.  Since the condensing steam is just a trickle at the bottom of the pipe it will freely drain regardless of the presence of a vacuum breaker.

The function of the vacuum breaker is so that when the TRV closes the vacuum can be broken to prevent additional steam from entering and the radiator continuing to heat when one does not want it to.

Without wading into who is right on this point - because it's over my head - would that mean swapping out this TRV for the Vent Rite 1 wouldn't be the best course?

gfrbrookline

So someone over tapped your hole. You need a 3/8 to 1/8 bushing.

https://www.supplyhouse.com/Bluefin-BLB038-018-3-8-x-1-8-Black-Bushing

EBEBRATT-Ed

@snootyusher

I don't know what size the radiator hole is but it's a standard pipe thread.

But a new vent which is 1/8" pipe thread. Then buy a 1/4" x 1/8 bushing and a 3/8 x 1/8 bushing which ever one matches the thread on the TRV to put between the rad and the vent.

Put the TRV back in before you leave for the store or you might have a mess if the heat comes on


For identification

1/8" pipe is .405 OD that's a little over 3/8" OD

1/4" pipe is .540 OD a little over 1/2" OD

3/8" pipe is .675 OD a little over 5/8" OD


Pipe is measured by the ID normally

gfrbrookline

@KC_Jones The way vacuum was described to me is that once a radiator vent closes the steam will condense creating a low pressure differential which will suck more steam into the radiator, high pressure goes to low, the suction of the vacuum created interferes with the radiators ability to drain the condensate, it sucks it back in like a syphon. The vacuum breaker releases that back pressure by letting ambient air into the radiator, not more steam, lets the radiator breath and the condensate to drain freely. An old MIT Professor put it in simpler terms to me a long time ago, poke a hole in a straw and you can't drink your soda since you don't have a vacuum.

This is why we have improved TRV's like the Danfoss and Macon which have a vacuum breaker built in prior to the thermostat and shuts the radiator off when it hits the set point but still lets it breath/drain.

gfrbrookline

@EBEBRATT-Ed good call, I was confusing ID vs OD, long day cleaning out the basement, too much coal dust.

gfrbrookline

Even with the vacuum breaker TRV's do not work well on 1 pipe steam systems.

snootyusher

EBEBRATT-Ed said:

@snootyusher

I don't know what size the radiator hole is but it's a standard pipe thread.

But a new vent which is 1/8" pipe thread. Then buy a 1/4" x 1/8 bushing and a 3/8 x 1/8 bushing which ever one matches the thread on the TRV to put between the rad and the vent.

Put the TRV back in before you leave for the store or you might have a mess if the heat comes on


For identification

1/8" pipe is .405 OD that's a little over 3/8" OD

1/4" pipe is .540 OD a little over 1/2" OD

3/8" pipe is .675 OD a little over 5/8" OD


Pipe is measured by the ID normally

based on my tape measure, it's definitely looking like the hole in the radiator is 3/8" wide, from one end across to the other

the "OD" references are over my head...but if I know the hole is 3/8" then that's the only bushing I'd need to buy, right?

snootyusher

Having a harder time sourcing Vent-Rite #1, seems like the Hoffman 1A is a good substitute. Any thoughts on that? thanks again for all of the great help here.

gfrbrookline

Basically you need a conventions vent. A 1/8 vent means the opening on the inside of the hole is 1/8" and the threaded outside diameter is 3/8". Sorry for the confusion.

snootyusher

gfrbrookline said:

Basically you need a conventions vent. A 1/8 vent means the opening on the inside of the hole is 1/8" and the threaded outside diameter is 3/8". Sorry for the confusion.

Oh, this makes sense now! So my 3/8" hole will fit a 1/8" vent (because the hole in the center of the vent thread will be 1/8" and all the way around it'll be 3/8"). Thank you! I just found a Vent-Rite #1 online so hopefully it'll come quickly. You guys are awesome. I hope this works and I'll report back. Thank you!

gfrbrookline

Where are you located?

gfrbrookline

If you are near Boston I can just give you one. I have some left over from when I balanced my building.

snootyusher

Really appreciate that offer but I'm not nearby. Thank you!

KC_Jones

gfrbrookline said:

@KC_Jones The way vacuum was described to me is that once a radiator vent closes the steam will condense creating a low pressure differential which will suck more steam into the radiator, high pressure goes to low, the suction of the vacuum created interferes with the radiators ability to drain the condensate, it sucks it back in like a syphon. The vacuum breaker releases that back pressure by letting ambient air into the radiator, not more steam, lets the radiator breath and the condensate to drain freely. An old MIT Professor put it in simpler terms to me a long time ago, poke a hole in a straw and you can't drink your soda since you don't have a vacuum. This is why we have improved TRV's like the Danfoss and Macon which have a vacuum breaker built in prior to the thermostat and shuts the radiator off when it hits the set point but still lets it breath/drain.

The only way the water can be affected is if the pipe is completely full of water.  In the case of the radiator that would be the entire bottom of the radiator or the valve or some other area that is filled with water.  If it’s not full, there is air present and a vacuum can’t do anything with the water.  It drains freely.

gfrbrookline

@KC_Jones I think we can agree to disagree, given my first hand experience with these Honeywell TRV's I think real world experience tells a truer story. What you are saying might be correct in a 2 pipe vapor system. As soon as I removed them from my buildings 1 pipe system the banging went away and the heat evened out.

ChrisJ

Just to keep the record straight I have TRVs on 5 out if my 10 single pipe radiators and they work fantastic.  So I disagree with the statement that they do not work well.  

All 5 do have vacuum breakers but I don't think they actually do anything at least not in my situation.  I'd have no problem removing them.

 I guess according to that theory no single pipe radiators can drain condensate when the vents are closed and the radiators are essentially at full output?  That seems a bit silly.  99% of single pipe radiators do not have any kind of vacuum breaker when the vents are shut and yet they drain fine.

All you need to replace that is a normal right angle vent like a Gorton #5.  It's a normal 1/8" NPT.

mattmia2

As long as the boiler is firing and steam is entering the radiator, the condensate can leave. It is when the boiler is no longer firing and pushing steam in to the radiator that i'm not sure what happens and probably is dependent on the exact configuration of the piping. Wet steam and unusually high condensate load may be a factor too.

ChrisJ

mattmia2 said:

As long as the boiler is firing and steam is entering the radiator, the condensate can leave. It is when the boiler is no longer firing and pushing steam in to the radiator that i'm not sure what happens and probably is dependent on the exact configuration of the piping. Wet steam and unusually high condensate load may be a factor too.

I think you're looking at it backwards in this case.
Pressure is what would be holding the water in the radiator, not vacuum.

Without a seal, there's no pressure differential to cause it to happen. When you hold your finger over the end of a straw and pull water up, it's the atmospheric pressure holding the water in the straw.

At least, this is how I understand it to work.

Look at mercury switches as an example. I believe more often than not those had a vacuum pulled on them.

KC_Jones

gfrbrookline said:

@KC_Jones I think we can agree to disagree, given my first hand experience with these Honeywell TRV's I think real world experience tells a truer story. What you are saying might be correct in a 2 pipe vapor system. As soon as I removed them from my buildings 1 pipe system the banging went away and the heat evened out.

Agree to disagree about physics, got it.

In the absence of a water seal between the 2 different pressures, there is no pressure differential for the water to "see". To have a pressure differential move water, requires the water to have those 2 different pressure separated. That is the actual physics of the situation. The water draining from a radiator is a trickle sitting on the bottom of the pipe, it can not create a water seal, and the velocity in that rad is so low it won't act on the water in a meaningful way to create a water seal.

Remember vacuum doesn't suck, the higher pressure pushes. So to prove your point, I am more than happy to listen to any explanation you have on how a high pressure pushes water laying on the bottom of the pipe, the pipe being mostly full of air/steam. So explain how that works, and I'm not asking about your thoughts on TRV's, I'm asking you to explain how that would work.

Your straw analogy actually proves my point, the straw is full of water. Lay the straw horizontal and see what happens. It will drain because the atmospheric pressure will push across the top and equalize allowing the water to drain, eliminating any vacuum the water was "seeing".

You have clearly stated that you put smaller vents on in addition to removing the TRV, and yet you persist in thinking it had to be the TRV. The smaller vent reduced the steam intake, reducing the condensate volume, which had the effect of eliminating your water hammer issue. It's that simple.

The TRV is not the problem, slope, too fast of a vent, pipe sag, those are your problems, one or all, but absolutely not the TRV. Basic mechanics and trouble shooting, never ever change more than one thing at a time when trying to diagnose a problem. You change 2 things, yet ignored one of the changes in your diagnosis.

To the OP, please don't give credence to the statements about vacuum holding up water, they are absolutely incorrect and will mislead you and others coming to this board.

One thing I will say, TRV's should not be added to a system until that system has been balanced and vented to the best it can be, only then should one consider a TRV to help with an isolated overheating problem.

I have 2 Danfoss installed, they work perfectly.

KC_Jones

snootyusher said:

KC_Jones said:

gfrbrookline said:The TRV is making your radiator retain water since it lacks a vacuum breaker which is likely causing your knocking sound.

This statement is factually incorrect.  The only way it can prevent water from leaving the radiator is if the supply pipe/valve are completely full of water.  Since the condensing steam is just a trickle at the bottom of the pipe it will freely drain regardless of the presence of a vacuum breaker.

The function of the vacuum breaker is so that when the TRV closes the vacuum can be broken to prevent additional steam from entering and the radiator continuing to heat when one does not want it to.

Without wading into who is right on this point - because it's over my head - would that mean swapping out this TRV for the Vent Rite 1 wouldn't be the best course?

Since you are in an apartment, it's honestly tough to say. Venting is a system, not just your radiators in your unit. It starts with main venting in the basement, then balance throughout the system.

That said, banging is either too aggressive of steam distribution, pipe slope, pipe sag, radiator slope, or most likely a combination of those. If you put a slow enough vent on that radiator it might, let me emphasize, might fix it. If the slope or sag is bad enough, you might not be able to get rid of it. The aggressive steam distribution typically is bringing to light a piping issue, but slowing it down enough, again, may fix it. The end result may be no banging, but remember you are also cutting down on the heat production of that radiator, so you could get cold, but, in an apartment, I would be doubtful of that being a problem.

EBEBRATT-Ed

Interesting discussion

If I am not mistaken they used to have vacuum air vents for one pipe steam which in my understanding could only be used for coal (continuous) firing, and that they had to be removed when firing gas or oil and standard air vents which will break a vacuum had to be installed