Vent Issue on a Two Pipe System

Phil945

I have a two pipe system with a Hoffman #76 main vent. The radiators do not appear to have traps on the radiators, but there seems to be a trap at a connection between the supply lines and the return lines.

The vent doesn't seem to release the air very quickly, and a couple of radiators on the second floor do not heat very well. I was considering replacing the main vent with a Gorton #2 to see if it would help, but wasn't sure it was the right decision. Any insight would be appreciated.

I have attached pictures of one of the radiators below, as well as of the system vent.

Jamie Hall

Thank you for starting a new thread on this -- and a little more information.

This system probably was a vapor steam system. As a result there may be either orifices at the inlet to the radiation, or at the outlets. Either way, it needs to run on very low pressure -- no more than say 8 ounces per square inch.

The traps from the steam mains to the dry returns are called crossover traps, and they allow the air coming from the radiators (and from the steam mains!) to get into the dry returns, from which it is vented by that main vent.

Back in the day that single #76 was adequate, and had the advantage that it would hold a vacuum, allowing a coal fire to continue producing steam at lower temperatures. We don't use coal any more... it has the disadvantage, from our modern standpoint, that it is a rather slow vent. Again, with coal, this didn't matter as a coal fire is slow to start -- but modern boilers are very quick, so you need a larger main vent.

The best way to do this -- as you have surmised -- is to add one or two Gorton #2 vents, or a Big Mouth vent, at the same location. You have the headroom there to do i, I think; use a T in place of the coupling, and place the vents on branches off to either side. You could use a shorter nipple coming up from the return, if you need more headroom.

Can you describe the rest of the system?

The other thing you will need to do to get it really happy is to use a vapourstat to control the maximum pressure; pressuretrols just don't operate at the low pressures you need.

Phil945

The boiler was replaced 6 years ago with the one shown below. The heating contractor did nothing to the system other than boiler replacement. Not having natural gas in our area, we chose to stay with a fuel oil burner rather than switch to propane.





There are two legs coming off of the boiler, the horizontal and the vertical 2 inch lines in the picture. It also has a domestic hot water coil, thus the two copper lines to the left of the unit. (We basically use it to feed hot water to the water heater in the winter months when we are using the boiler.) The condensate return line is the one coming out of the shadows into the back of the unit. The garden hose allows me to drain the water directly into a floor drain when I skim the boiler.

All of the radiators in the house look like the one in the pictures above

Here is a picture of the junction of the supply lines with the condensate return line.



That's basically it. Every other connection is a direct pipe fitting. No traps or vents other than what I have shown in the pictures.

Jamie Hall

It could be worse... the near boiler piping isn't ideal, but if you get decent heat with no banging., OK.

However, you will want to add a vaporstat, as I mentioned previously. You can add that next to the existing pressuretrol, and wire it in series with it. Try setting it at a cutout of 12 ounces at first, then try dialing it down to say 7 or 8 ounces and see how it goes. In addition to adding vents...

Phil945

Here are close ups of the front of the boiler, the back of the boiler, and the check valve (?) on the return line, about three feet from the boiler.

nicholas bonham-carter

Why is there a check valve on the return?--NBC

Phil945

Thank you Jamie.

I am ordering two Gorton #2's, as well as fiberglass pipe insulation (I just had the asbestos removed from all accessible pipes in the basement and crawlspace). It will be interesting to see what the difference in heating and fuel consumption will be.

I plan to add the vaporstat sometime in January.