Second vent on upstairs radiators to help balance system?

DavidK_2

Hi,
I have a cape cod style house. Built 1938. Single pipe steam heat.

I have a problem that the upstairs gets too hot when recovering from setback, and is too cold when running at thermostat set point. The thermostat is on the first floor.

I tried searching but could not find a related discussion. Perhaps I searched wrong.

We run an 8 deg setback. I could reduce that, but wife insists on setting back the temperature at night and I also like sleeping in a cooler house.

The main steam runs in basement seem to be vented OK. Steam arrives at all first floor radiators at about the same time. It takes longer for steam to reach the second floor. The runners for the second floor branch off the main lines. These runners are smaller pipe than the mains, and as near as I can tell are not vented.

Here is what I think is happening.
From setback the upstairs radiators get too much steam because the existing radiator vents are bigger than the downstairs vents.
When running at set point the upstairs radiators do not get enough steam because the thermostat is satisfied before the radiator vents upstairs can vent the runner pipes.

I think the solution to this is to vent the upstairs runners fast, then put in a smaller radiator vent so the radiator itself does not heat up too quickly. The thinking is that during setback recovery the radiators will fill more slowly so the room does not overheat; during set point operation steam gets to the upstairs radiators at about the same time it gets to the downstairs radiators.

Does this all make sense?

If so, how do I best implement this?
I'm not sure how to add a vent to the end of the runner pipe itself. There is a short run of pipe between wall and radiator valve. Perhaps I can drill and tap that for a vent?
I'm wondering if instead I can add a big vent on the side of the radiator closest to the steam pipe entry.
There seems to be a cast molding identical to the one on the other end of the radiator (the far end that already has a vent). My thinking is perhaps I can drill out that bung out, tap it, and put a big vent there. Drilling a molded bung is probably easier then drilling a round pipe. The idea is that increasing radiator venting would get steam there faster, then when it reached the newly added first vent it would close, and the existing vent would control how fast the rest of the radiator filled.

Tips on drilling and tapping appreciated. I've never done this in cast iron, but assume similar to steel.

I'm thinking about getting 4 of these (two for each radiator).
https://www.amazon.com/dp/B009ATMA2I/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=26PM1JRBOPIMI&coliid=IDCZGWAR2HV6A

Abracadabra

Yes, you can do what you are saying, use MOM#D as a vent on the supply side of the radiator. Not a fan of the varivents.

New England SteamWorks

Hatterasguy said:

You are correct in your analysis.

What we do is to adapt the radiator valve (not desired on one pipe anyway) and install a Gorton #1 in its place.

The risers are now vented fast enough to bring steam quickly to the second floor and the rad vent can be properly calibrated for the heatless of the room.

In other words @DavidK, Hatterasguy is suggesting (and I concur) replace the steam valve with a tee and a union and put a vent on the tee. Personally, I would go with @Sailah 's Vari-Vent, not to be confused with other variable vents.

New England SteamWorks

Even easier: Open your window at night. That 8 degree set back is a lot of work for your boiler. Not efficient, and has to be cycling on pressure.

DavidK_2

I think I'll buy an 1/8 ntp tap, and a gordon #D. Try it in one upstairs radiator. Any warnings, or tips, before I do this?
If it works out I'll do the same to the other radiator

I don't want to open the windows at night. That would be throwing heat away. I don't want to replace the valve with a vent. If nobody is living up there I want to be able to shut off heat

RomanGK_26986764589

@DavidK I believe there is no need to shut off radiators in unused rooms. It can make the boiler even more oversized.

DavidK_2

I agree. I've never had, or wanted, to close a radiator valve. The only time I can think I might want to do this was if for some reason I had to remove a radiator and still have heat in the rest of the house. But I'm reluctant to try a repipe during heating season. Likely a T and vent is the way to go. But I'd hate to bust a pipe trying to do it. I've got two #D and one #5 ordered. Should be here today (currently one radiator has a #c, the other has a #5). My plan is #d and #5 in each radiator. I should know in a day or two if my plan works. I suspect it will help, but might require some tweaking.

ChrisJ

You may also have the option to drill and tap the pipe side of the radiator and install a vent there. It will perform the same function as one mounted on the pipe. I only mention it because it may or may not be easier than other options.


Also, regarding sleeping in a cooler house, I too like that but I stopped doing setbacks. I now have TRVs in two of our bedrooms and they keep those rooms around 64F while the rest of the house stays 72F.


How long are all of your pipes?
I drew up a diagram of all of mine and have kept updating it over the years. I even spent time calculating the pressure drop to each radiator from the boiler.

Believe it or not, knowing that pressure drop actually makes selecting the right vent much easier.

I do need to update it again, I eliminated the pipe vent in the main bedroom and went up to a Gorton 5 on the radiator. This was because I found running 2 CPH was much more tolerant of a faster vent in that spot and didn't cause overheating. That, and the Gorton 4 was too slow on windy nights.

DavidK_2

It is interesting you monitor pressure. How do you do that? I've been thinking about monitoring temperature. Even that is pretty expensive. I would like to monitor when the furnace turns on, when it turns off. When it does that due to thermostat or due to pressure. For now I use my hand to determine if there is heat at each radiator.

DavidK_2

I think the reality is single pipe systems were designed for when somebody was at home to monitor the home fire. I don't think they were designed for on/off boilers.

ChrisJ

I only monitor pressure with my eyes and a Magnehelic, nothing keeps track of it. The pressure drops to my radiators are calculated, not actual.

The single pipe systems were originally used with coal fire systems, but that doesn't mean they can't work just as good, if not better as an on/off system. Mine works beautifully, but it took time to get there. All radiators get steam within a few seconds of each other.

Have a look at the pictures of my system found at the link in my signature.

hboogz

@ChrisJ How are you calculating pressure drop? What's your method? Your diagram is great, BTW.

@DavidK what's considered cool to you temp wise? Have you been running this 8 degree setbacks through multiple winters? Especially where you're located, that seems like a really big setback when you can probably get what you need done using TRV's, or the right venting at the radiator. Vent-Rite 11's have worked wonderfully for me at controlling the temperature between two floors and calming down rads that overheat.

I have one-pipe system in Queens, NY and two floors with 9 radiators and found that no setbacks have been working well for me so far (my first winter trying no setbacks) I also have 2 Gorton 2's on the long main and a hoffman 75 on a short main (which i need to change)

At my brothers house i don't have access to the basement mains and can't open the ceilings this season to do the work, so venting @ the radiator valve is something I have to get done to get the system working better especially when the tstat reaches the setpoint and the second floor is cold. (tstat on first floor)

LionA29

@DavidK
The "correct" DRILL BIT size for a tapered 1/8-27 pipe thread is "Q" or .332".

DavidK_2

I was going to use 21/64 drill. Pretty close. But I probably have a Q. Would you suggest drilling a pilot hole?

LionA29

@DavidK - It Wouldn't hurt, just take your time. If you are unsure, get a piece steel block or something thick and do a test drill and tap. This way your drill and tap comes out perfect.(if you want to

hboogz

@davidk & @LionA29 any place online where I could buy these bits that you know of ?

Sailah

ebay, McMaster Carr, MSC Direct, Fastenal has stores, Amazon

ChrisJ

hboogz said:

@ChrisJ How are you calculating pressure drop? What's your method? Your diagram is great, BTW.

It's been a long time, I honestly don't remember what I exactly did.
I believe I found charts online that showed the friction loss at a certain amount of flow etc. I do remember it took a long time to do it though.

DavidK_2

Holes drilled and taped. New vents in. Steam seems to get to the radiator much faster now. Arrives about the same time as downstairs Right now have #d on supply side, #5 on far side. Might need to step down to #4, time will tell.

The first hole was taking a long time to drill, then I learned you are supposed to drill cast iron dry. That made drilling much easier as faster

hboogz

@DavidK never tapped myself. Thanks for the tip about cast. I certainly had no idea. Safe to say on black scd40 you need cutting oil while you slowly drill? Did you start with a pilot hole?

Sailah

Sharp bit, heavy pressure, cutting oil for steel.

Same for cast iron but drill dry.

Light pressure and high speed heats up and dulls bits. You want the heat to come out of the hole in the chips not the bit or work. Ideally

DavidK_2

I used pilot hole on first one. On second one just went straight to final size. Worked fine.

LionA29

Post that pic of the valve tap @DavidK

DavidK_2

@LionA29 not sure what you are looking for. Here is the tap I used https://www.amazon.com/gp/product/B000K1LZ76/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

LionA29

@DavidK
The pic of the new vent valve you drilled and tap installed on the rad inlet

LionA29

@DavidK
How is the heating of the rad now that you have that extra vent?

hboogz

awesome thread. @DavidK Thanks for the reference for the exact drill bit you used. Curious about the bit that @LionA29 mentioned.

And please do send a pic of the newly installed vent and tap when you have the chance.

Harry

DavidK_2

Heating is better upstairs than before. Will take some monitoring. Probably several days to see how much difference it makes.

Since son and girlfriend are currently living up there I can't monitor as much as I would like. It takes me several heating cycles to tell if the change was worth it. And I have a day job. And my day does not correspond with theirs.

So far things look positive. I'll try and post a picture later, but it is not very exciting. There are now two vents on each radiator. A big vent on the supply side (which I just added) and a smaller vent on the other end.

I think it going to take some more tweaking. I might need a smaller radiator vent. I might need to reduce my setback. That kind of tuning takes weeks in my house

DavidK_2

I'm curious about how a TRV would react in my environment. As I understand it they are usually connected between radiator and vent. Which means they are monitoring the near radiator temperature. Which means if the radiator is full of steam, they would shut off. Am I missing something?

LionA29

@hboogz
Apologies.... drill bit correction.
Drill bit "R"!

DavidK_2

My tap said drill bit 11/32. I used 21/64 (since it is easier to make bigger hole if required). In order of size: 21/64, Q, R, 11/32. Probably any of them would work fine.

Lets see if I can attach a picture of radiator. New vent is on left.


It seems to work well. Vent on left is #d. Quickly vents riser. Shuts when steam hits it. Then vent on right takes over and slowly fills radiator.

I think I'll change to a 6 deg setback. It has to be darn cold outside to hit the old 8 deg. Most nights we will not even reach 6 deg.

LionA29

Hey @DavidK ,
That new left vent should be on the supply pipe coming out from the wall before the shutoff valve.
More members may confirm this later also.

LionA29

That is my rad pipe vent.

DavidK_2

@LionA29 I know. But it was easier to drill out an existing bung on the radiator than it would have been to drill the pipe. The result is about the same. Once that bottom 6" on left of radiator gets steam the vent closes.

LionA29

@DavidK
The idea was to bring steam to the rad faster which requires to vent the supply pipe off the main if it's a long run. By venting that pipe, steam will come to the rad and the correct vent on the right side will slowly vent the rad.
It may work what you have there but it will be far more effective the way it should be done.

DavidK_2

@LionA29 I don't think it makes much difference. I'll just pretend the first 6" of radiator is part of riser Saves me from moving radiator and re-piping.

ChrisJ

DavidK said:

I'm curious about how a TRV would react in my environment. As I understand it they are usually connected between radiator and vent. Which means they are monitoring the near radiator temperature. Which means if the radiator is full of steam, they would shut off. Am I missing something?

TRVs aren't perfect.
They do sense temperature right by the radiator, also, right by the cold wall.

I use Danfoss TRVs which have vacuum breakers, this is very important. Next, you need to make sure you vent them at about the speed you'd want without a TRV, maybe a hair faster but not much.

The deal is, the TRV works best at keeping the radiator from heating during a cycle. It can also throttle the venting to an extent and slow the heating down. My two radiators with TRVs often don't heat at all (sunloading, people in the room etc) and when they do heat, it's usually only partially because the TRVs are throttling them.

However, once X amount of steam enters the radiator it will continue to heat that much until the boiler shuts down even after the TRV has closed. Once the steam is in there, it's not leaving until the system shuts down. As the steam condenses, it pulls new steam in behind it, no vent needed. This is why venting somewhat slow is important. If you vent super fast the radiator will fill, the TRV won't have time to react and the room will overheat.


So to answer your question no, once the end of the radiator the TRV is mounted on is hot, the radiator will continue to heat even after the TRV is shut.


I also found 2 CPH works much better with TRVs than 1 CPH.

I have TRVs on two bedroom radiators, and want to add them to a kitchen radiator and a livignroom radiator as well.

LionA29

@ChrisJ
Thank you, very welcome explained. Which Danfoss model trv do you have?

hboogz

Thank you @ChrisJ.

@LionA29 & @DavidK will this tap work ?

https://www.fastenal.com/products/details/55283

DavidK_2

@hboogz That tap looks perfect

DavidK_2

@ChrisJ also thanks. What is CPH ?