2-Pipe Steam radiator with vent?

Cyclone33

Hi - I have a 2-pipe steam radiator system. My house has a basement and 2 floors above. On the main floor, 1 radiator has a vent on it and upstairs 1 radiator has a vent on it. Hoffman vent #41 - max 10psi. There are 4 radiators total upstairs and 6 total on main floor. Should this be like this? Was someone trying to get air out and heat system faster? I attached picture of one. I do have the trane vapor system on most the radiators. Nothing seems to be stuck in return. Radiators seem to be heating fine. I just thought a 2-pipe shouldn't have vents. Thanks in advance!

Jamie Hall

Quite correct. Two pipe systems don't need vents on the radiators -- although the one in the picture may help that radiator heat sooner, it won't help it heat -- it will (or should) close almost immediately.

When you say you have a Trane system on "most of the radiator" what do you mean?

I might add -- if it ain't broke, don't fix it. But it might be fun to know more about what it should be...

Cyclone33

A couple of the radiators have a steam trap on the radiator at the return instead of the trane vapor system setup.

The vents do open and close quite often

Cyclone33

I was just wondering if loosing steam out the vent was hurting my system efficiency.

Jamie Hall

Shouldn't be losing steam -- just air.

Steamhead

@Cyclone33 , can you add some pics of the radiator return connections, and the boiler including any Trane devices in the piping around the boiler?

Where are you located?

Cyclone33

 All of the boilers except for 1 have the trane return elbow. The other has the steam trap shown below.

I live in eastern iowa in farmhouse built in 1870 so lots of things patched together over the years. 

Jamie Hall

That system should work well -- with some tweaks. First, make sure the pressure control is set low -- cutout of 8 ounces per square inch or less. If yours won't go that low, you will need a vapourstat.

Second, that poor old vent may not be adequate. I'd suggest a Gorton #2.

Steamhead

@Cyclone33 , referring to the diagrams in chapter 15 of @DanHolohan 's "The Lost Art of Steam Heating", which you can get here:

https://heatinghelp.com/store/detail/the-lost-art-of-steam-heating-revisited

It would appear that the ancient Hoffman #75 main vent in the first pic is at the end of the steam main. Is that the only steam main in the system? How long is it, and what pipe size?

The air from the radiators is supposed to leave through the special Trane return elbows and pass through the dry (overhead) returns to the cast-iron cylinder in the piping just behind the pipe the Hoffman vent in mounted on. This cast-iron cylinder is actually a venting device, and contains a float which will rise and shut the vent opening if the water backs up into it. If this thing doesn't vent, the system won't heat well, and some knuckleheads will try to "solve" the problem by venting the radiators. Can you post a pic of the top of the cylinder?

Cyclone33

It has a Hoffman #4 quick vent. It does seem to be venting air/steam, but has spit water out before. Could the float be stuck? @Steamhead

Would you suggest replacing the Hoffman 75 with an exact replacement? That is the only main vent. It does seem like the cast iron cylinder does most of the venting. 

I blow the system down once per week.

@Jamie Hall

You are suggesting the Gorton vents on the radiators that have a vent now? 

Cyclone33

@Steamhead the main vent is on 1.5” pipe. Estimating total run is around 130’. The pipe does change size a couple places 

Steamhead

OK, here we go:

Since you say the steam main with the Hoffman vent is the only main in the system, and it changes sizes but ends as 1-1/2", start off with three Gorton #2 vents where the Hoffman is now (each Gorton #2 will vent four times as fast as that Hoffman #75). You'll need to build a manifold to hold them, consisting of several 3/4" nipples, a 3/4" elbow, two 3/4x1/2 tees and a 3/4x1/2 90° elbow. There are a couple pics in the slideshow that's part of our Find a Contractor ad to give you an idea what they might look like:

https://heatinghelp.com/find-a-contractor/detail/all-steamed-up-inc

Replace the Hoffman #4 with a Gorton #2.

Why do we need such big vents? Remember, the original boilers on these systems were coal-fired. With coal firing, the steam only came up once a day, so slow radiators didn't matter as much- once all the radiators got hot they stayed hot. But with oil or gas firing, we don't have that kind of time. So fast main venting means better comfort and reduced fuel consumption.

I'd also replace that Pressuretrol with a Vaporstat. These Vapor systems were designed to run at ounce pressures, and too much pressure can cause the main vents to spit.

Cyclone33

Ok, that makes a lot of sense. Thanks so much for explaining that and offering advice. @Steamhead

Would you remove the Hoffman #41 vents that are on 2 of the radiators or replace them with gortons? 

Is there a vapor stat anyone would recommend? 

Jamie Hall

If you could locate a new old stock mercury Honeywll Vapourstat, the real thing -- that would be the way too go. The newer ones are usually OK, but sometimes not. Get a low pressure gauge to go with them.

Cyclone33

What setting would I need to be around on the vaporstat or how do I determine correct settings? 

Thanks! 

Jamie Hall

No more than 8 ounces for the cutout and a differential of 4ounces, giving you a cutin at
ounces. That would be the maximum. Slightly less would be better.

There is a procedure for determining both the optimum settings and whether you have adequate main venting. It requires a low pressure gauge -- but isn't difficult.

Start with a cold boiler. Fire it up and observe the low pressure gauge. As steam starts to rise, the pressure may rise slightly -- typically to two or three ounces per square inch. Now if the pressure stabilizes there, or very nearly so, as the system as a whole warms up, your main venting is adequate. If it continues to rise, however, then more main venting is needed. At some point, depending on how well matched your boiler is to the system, the pressure will start to rise again (this may take, with a well matched boiler, as much as 45 minutes to an hour). Somewhere around twice the pressure which was achieved before the rise started is the highest cutout pressure you want to have -- but not, as I say, more than 8 ounces.

Now if your boiler is significantly oversize -- which is quite common -- that stable or nearly stable pressure plateau may be quite short -- 10 to 15 minutes even, perhaps, But the principle is the same.

Steamhead

Cyclone33 said:

Ok, that makes a lot of sense. Thanks so much for explaining that and offering advice. @Steamhead

Would you remove the Hoffman #41 vents that are on 2 of the radiators or replace them with gortons? 

Is there a vapor stat anyone would recommend? 

Remove the radiator vents and put plugs in the holes- with the new main vents in place of course. If they then don't heat, clean the holes in the return elbows.