Missing main vents?

gattu_marrudu

Hello,

I inherited a steam system in an early 1900s house I bought a couple of years ago. Tired of paying high gas bills in the winter, I decided to read more about it and understand what's wrong with my system.

This is a one-pipe, gravity-return system with two mains. The heating is on 2 floors of a less than 2000 sqf house. The boiler is a 150 MBTUh Utica with 2 risers to the main. The system looks like it was recently upgraded with (alas) copper in the near-boiler piping, and maybe a new radiator on the far end of one main. Most of the main and radiator risers look original.

First thing I noticed was that the pressuretrol was cranked up to 9 + 1 PSIG. I took that down to the standard 0.5 + 1. But I also wonder if someone had raised the pressure because of another symptoms. One may have been that the near-boiler piping was stark naked (that denim blanket and aluminum/fiberglass I added later).

Now it's summer and I haven't fired up the system yet to verify if my settings work.

I also noticed that there are no main vents on either main. The picture below is the last riser (left) on one of the mains, and the possible recent addition (it's copper, and I think it's pitched wrong because it bangs a lot):

This is the end of the other main with the last 2 risers (one to the 1st floor, one to the 2nd):

According to what I read, I should see a main vent after the risers, at least 15" from the return elbow. In either case, there is no vent, nor there is any room for adding one to spec, because in both branches the return elbow is right next to the riser.

How should I go about this?

Thanks in advance.

gm

Steamhead

First off, the insulation at the ends of those mains looks like asbestos. Have that removed by a licensed abatement contractor.

After that, the vents can be installed in one of several ways. How long are these mains, and what pipe size?

gattu_marrudu

Yeah, that's asbestos. A plumber told me to just wrap it up in tape and leave it there because that's the best insulation. Dunno if that's good advice. I decided to get back to that once I figured out the system design problems.

The mains are 25' and 30' long, pipe OD is about 3".

Steamhead

If you're going to work on those pipes, the asbestos has to go. Do that before the main vents.

gattu_marrudu

Gotcha. I'll be back.

ethicalpaul

The near boiler piping is laid out wrong. I personally wouldn't worry much about them being copper—it's not perfect but it's not going to hurt anything. The near piping being insulated isn't going to have a meaningful affect on the boiler's operation, but with that piping layout you must ensure you have good water quality (clean with no oil) to avoid "carryover" or "surging" where water gets thrown up into the main.

With that, and assuming the pitch of the main and radiator supply pipes are correct, you can have good operation with this setup. The vents will be good to add, but I agree with @Steamhead. Get the asbestos out of there. You will likely have to when you sell the house anyway.

gattu_marrudu

For completeness, I may as well attach the manufacturer's recommendations:

Yeah, my piping seems a little bit off, especially the long horizontal connection in the Hartford loop.

Re. insulation, I was reading in Dan Holohan's book that if the header cools down faster than the main, it can pull the steam back in the off cycle. That's how I understood it, at least. Also, it was wasting a lot of heat in the basement, that's why I threw in that blanket.

What insulation material do you recommend after I remove the asbestos?

ethicalpaul

when the boiling stops, the steam in the entire system will collapse at basically the same time. That is not a reason to insulate your near boiler piping.

the reason is to prevent excess heat in your basement—to keep the heat going where you want it, in the living space.

you can insulate your mains with fiberglass

ethicalpaul

Here's IMO the best place to buy pipe insulation. Again, you don't really need it, pipes don't radiate that much heat, but if your basement is hot and you'd like that heat in your living space, then go for it. But don't expect a good return on investment

https://www.buyinsulationproductstore.com/Fiberglass-Pipe-Insulation-SSL-ASJ/

gattu_marrudu

OK, the asbestos insulation is gone.

I got some better close-ups of the bare main pipes — the two main branches:

End of left-side branch:

End of right-side banch (two risers on the right):

I measured the bare main pipe with a caliper. It starts at 2.375 and scales down to 1.9 as risers branch off.

Back to my original question: where and how should I install main vents?

And also, since it looks like this system has never had vents, would there be a reason it would work just fine without them?

Thanks.

mattmia2

It might have worked ok without main vents with the original coal boiler where it essentially just ran one long cycle. It needs main vents to work efficiently with a boiler that cycles.

Getting the steam up to 9 psig wastes a ton of fuel and the higher temp of the boiler increases losses to the basement. Make sure the radiator vents work and you will probably have to play with the sizes to balance the system. I'm betting the system isn't venting at all and they cranked up the pressure until it compressed the air enough to get some heat. This will waste a lot of fuel.

The main vents can be teed in to the risers from the wet returns and put in their own riser to keep water out of them.

If the wet returns aren't far enough below the water line they could be the source of the banging. When the pressure was at 9 psig it could have been pushing the water out of the returns. If they don't have water in them steam can get in to them and collide with water and bang.

The near boiler piping is wrong and could also be the source of the banging, especially before it gets hot while it is producing a lot of condensate that has no place to go but back down in to the boiler colliding with the steam exiting the boiler. The header should slope to the equalizer so the condensate drains in to the equalizer. The various twists and turns and horizontal sections of the equalizer above the water line also leave lots of places for water to collect and collide with steam.

gattu_marrudu

The main vents can be teed in to the risers from the wet returns and put in their own riser to keep water out of them.

Like this?

The banging is localized in the last radiator on the left (second pic in my previous post), which also takes hours to heat up. The pipe is pitched toward the radiator, I guess that is the cause of the banging. Strangely I have never heard any noise from the near-boiler piping, even the very long Hartford nipple, but I'll listen more closely next time I'll fire it up.

Thanks for all the good advice.

neilc

I don't think those pipes look as clean as they should,

does that white patchy stuff have fibers to it?

mattmia2

https://forum.heatinghelp.com/discussion/comment/1809260#Comment_1809260

That would be ideal but it would also work if you did something like this:

if the banging is only at one radiator you might get lucky and just need to raise the end of the runout (and probably the radiator). trapped water will kill the steam and keep the radiator from heating until the steam evaporates the water.

gattu_marrudu

That would be ideal but it would also work if you did something like this:

That would definitely be more convenient, as I saw they sell "saddle" tap tees that don't require splicing and re-threading iron pipe: https://www.mcmaster.com/products/saddle-tees/low-pressure-iron-and-steel-threaded-pipe-fittings/ I never used them so I can't tell if they are any reliable. Many advise against those tap tees that pierce copper pipes to add a water feeder, I wonder if these have the same issues even at lower pressure than water pipes.

Alternatively, I guess I'd have to rent a pipe threader, put a union in the longer wet return, unscrew the 100+ year old iron fittings and replace the elbow with a reducing tee.

gattu_marrudu

https://forum.heatinghelp.com/discussion/comment/1809261#Comment_1809261

It feels chalky, I can't tell if I can see fibers.

Since I'm going to re-insulate the pipes, I'd rather not disturb what's there. Rather than scraping it off and letting it fly around, I thought of spraying some varnish or paint on it prior to putting the new insulation on, so it would stick to the fittings permanently.

gattu_marrudu

Now, for vent sizing:

I measured the lengths and diameters of the main branches. According to the charts in Dan H's book, I should have 0.39 and 0.53 cf of air volume respectively. I am also looking at the main vent charts and I'm a little confused about how to read them. The ratings are for 1 to 3 ounces of pressure. But isn't my boiler pressure 2 PSI, i.e. 32 ounces? What pressure are we talking about here? And since the ratings are for cf/minute, how fast am I expecting to vent the main?

P.s. I'm referring to info that's also available on this site: https://heatinghelp.com/systems-help-center/balancing-steam-systems-using-a-vent-capacity-chart/

ethicalpaul

Ignore the pressures in those charts. Your boiler pressure is whatever it currently is. It could be up to 9psi if your pressuretrol is set that high (and if your boiler is oversized) but you want it to always be below 4 ounces/SI

When your boiler starts boiling, the pressure is going to be low and you want enough main venting that it stays nice and low. Then the steam will start to arrive at the radiators where it can rapidly condense, keeping your pressure low.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1809281#Comment_1809281

Better hardware stores and pluming supplies can cut and thread pipe for you once you get it apart and figure out what you need. Pre-threaded nipples are also available. If you scrub it with detergent before you assemble it and use teflon tape only your might get away with not skimming the boiler. If the oils from the new pipe and dope get in to the boiler you will have to skim the boiler(if they exist inside the pipe they will work their way to the boiler.)

If you are lucky you can cut the pipe near the fittings and unscrew it with a pair of large pipe wrenches. If you put a rod or pipe inside the pipe about the same size as the id of the pipe your chances of it unscrewing instead of collapsing and shearing off are much greater. If you do have to cut it apart you can either cut the pipe almost flush with the fitting and cut 2 slots inside the fitting almost to the threads and knock the piece in between out with a chisel, you can cut the fitting almost to the threads then put a big hammer or other large chunk of steel/iron behind the fitting and hit the cut with a chisel to split the fitting and it will unscrew. The third option is that some fittings are made of brittle iron that will shatter if you put a large hammer behind the fitting then hit the fitting with another large hammer.

gattu_marrudu

https://forum.heatinghelp.com/discussion/comment/1809294#Comment_1809294

So… for, say, venting 0.39 cf, a Hoffman #4A, that is rated at 0.216 cfm @2 oz, would completely vent the main in less than 2 minutes… would something in that ballpark be a good starting point?

Steamhead

https://forum.heatinghelp.com/discussion/comment/1809308#Comment_1809308

No. You want to vent at the absolute lowest pressure you can. Start with one Gorton #1 on the shorter main and two Gorton #1s on the longer one.

ethicalpaul

You want to vent at the absolute lowest pressure you can

Well that's hyperbole, but I like your size suggestions.

I'd suggest Maid O Mist #1 vents to save money. They are functionally identical

https://www.supplyhouse.com/Jacobus-Maid-O-Mist-J1-1-3-4-x-1-2-Main-Vent-Valve-3563000-p

gattu_marrudu

OK, I think I'm starting to get it. Thanks for walking me through the process.

If I understood correctly, I'll want the lowest resistance possible in the main vents, so that the steam will reach all risers before it starts to go up. And it won't go up until it has filled the main, and the main vents shut down, because the radiator vents are slower and offer more resistance.

At that point, if I get the ratings of the radiator vents proportional to the volume of each radiator and its riser, I should have a balanced system that heats up evenly. Right?

But then,

Start with one Gorton #1 on the shorter main and two Gorton #1s on the longer one.

My branch volumes have a ratio of 1:1.37. If the vents have a ratio of 1:2, will they vent unevenly? Would, say, a Maid O'Mist or Gorton #1 (0.54 CFM @ 2oz) and a Hoffman #75 (0.75) be much closer to the volume ratio (and save me the extra fittings for the additional vent)? Will it matter?

mattmia2

The speed at which the main heats is not just the speed at which the air can get out, the steam also needs to heat the main to steam hot before it can progress, it will condense to water until the main is hot enough so the speed at which it will progress is also a factor of how much mass is in the main. On a cycle where the mains are already hot from the previous cycle this will be faster.

ethicalpaul

it won’t matter much if one main’s vent(s) closes before steam reaches the other main’s vents.

when the first main vent closes, then almost all of the produced steam will go to the other main until its vent(s) close. As you said, the radiators vent slower

Steamhead

Try it. As long as the steam reaches the ends of the mains within about 30 seconds of each other, you should be fine.

dabrakeman

https://forum.heatinghelp.com/discussion/comment/1809282#Comment_1809282

Painting the pipes is fast and easy and gives some peace of mind if fear fibers may be left. The application of paint is less likely to disturb fibers than sliding on and off dry fiberglass insulation. For future everything is sealed. I painted mine all black. Could get some minor smell first time they get hot.

gattu_marrudu

Now dealing with taking apart the old fittings.

If you are lucky you can cut the pipe near the fittings and unscrew it with a pair of large pipe wrenches. If you put a rod or pipe inside the pipe about the same size as the id of the pipe your chances of it unscrewing instead of collapsing and shearing off are much greater. If you do have to cut it apart you can either cut the pipe almost flush with the fitting and cut 2 slots inside the fitting almost to the threads and knock the piece in between out with a chisel, you can cut the fitting almost to the threads then put a big hammer or other large chunk of steel/iron behind the fitting and hit the cut with a chisel to split the fitting and it will unscrew. The third option is that some fittings are made of brittle iron that will shatter if you put a large hammer behind the fitting then hit the fitting with another large hammer.

All these options require to destroy the fittings and/or hitting hard on a very old pipeline that I'm not sure how it will take the blows.

I'm trying a less invasive approach first, spraying some Liquid Wrench into the fittings and letting it soak in for a couple of days, spraying again every 24h. Then I can try prying the thread loose with a rod or pipe just a bit smaller than the nipple ID.

Long Beach Ed

If you are going to try penetrating oil, use a wire wheel on a drill to clean the rust and sealer from around the threaded connection first. When you spray the threads every day or so, rap the connection with a lump hammer to vibrate the connection. Sometimes you'll get them free this way. Sometimes not.

gattu_marrudu

After a week of banging, spraying, and torching, I decided to move on to the angle grinder and cut the fittings free. Too bad for the old fittings—nice hunks of pre-WWII metal, before that good stuff went into bombs & tanks. I can see the thick rim of rust was mostly inside, that's where the lubricant couldn't get to.

The vents are finally in. I had to do some twists & turns due to the placement of the main's ends below studs, but I was able to keep some elevation. The vent holes are very close to the ceiling, one just about 1/4". I don't know if this would be a problem if they spit humid air at one point in the wood. What do y'all think?

ethicalpaul

I think it's fine. You could have gone 1/2" up to the vents but it's all good.

What is the size (sizes) of that tee you put at the end of the main? Oh I see it looks like it's reducing to 1". That is probably OK

gattu_marrudu

Yes, the tee is reducing 1 1/2" to 1" and then to 3/4" to each of the vents. Maybe oversized, but it didn't make much difference in price or maneuvering around.

mattmia2

You could shorten it up by using some street fittings. You could shorten it up more by combining your reducers and you ells but I'm not sure if there are reducing 45s or reducing street 45s.