Main Vent Capacity Analysis

SteamySwede

I'm a steam newbie in first winter in an old house with a 2-pipe system and fuel bill seems a bit high.  Tons of possibilities I know. House is 4k sf with 25 radiators. Gas-fired boiler is Weil-McLain EGH-95 rated at 400k btu input and 320k btu output.  I've been reading up in Dan's books so trying to get smarter. 

Boiler is not short cycling and system is working very well; cut-in at 0.5 psi, cut-out at 1.5 psi and pressure gauge never moves up to 1 psi so running low pressure and heats quickly. 

Pipes generally insulated in basement with asbestos, no clue about vertical runs so lack of insulation could be an issue.  Is there any way to check this short of opening up the walls (runs are completely hidden)?

My other thought was that main venting could be inadequate.  I'm in process of mapping out basement distribution (lengths and pipe sizes) but not sure if I need to guesstimate vertical runs as well.  Is there a post or guidance on how to calculate system capacity? 

The system has 8 main vents that I've found (a variety of types that I can't identify)

- 4 on supply mains (3 at drip connections, 1 mid-stream on a supply main)

- 4 on dry returns

I can post pics of vents, boiler setup, etc. if helpful. 

Thanks in advance.

Steamhead

Definitely take pics and post them

main venting is important. I've talked about that in your Mystery Fitting thread. 

SteamySwede

Main Vent Pics

Here are pics of the vents that I have found, the pic names indicate if they're on a supply line or on a dry return.  The mystery box is one of two on that dry return in same area.



Main Supply Vents: 3 x Hoffman 4A's, plus one mystery vertial, cylindrical vent.



Dry Return Vents: 2 x Hoffman 4A's, 1 Hoffman 75, 1 Hoffman 76A and one mystery cube vent. 

Thanks for guidance.

Steamhead

The mystery cylindrical vent

is probably a Dole but I'm not 100% sure of this.



Next step is to measure the length and diameter of each steam main, from the boiler to the vent location. This will tell us how much air is in each main that we need to vent on start-up. Also, how many radiators are connected to each of the dry returns?

BobC

Need more venting

I would guess you need more venting, once we know how long and what size the mains are we should be able to tell you what vents you should have.The enclosed chart will help you determine the sizes.



I'd be very surprised if the vertical risers are insulated but if your sidewalls have blown in insulation that should help keep the pipes in the exterior walls snug and the interior runs should be contributing heat to the house. House insulation is probably your best bang for the buck.



A house this large could probably benefit from a vaporstat instead of the pressuretrol you have now, low pressure saves fuel. Also don't trust your 0-30 PSI gauge, I would install a 0-3 PSI aux gauge so you know what the pressure really is.



Bob

SteamySwede

Questions

Two questions come to mind as I try to figure out the answers:

1) Does it matter what size the radiators are?  Some are very small and others are quite large.

2) When there is a vent on the dry return at a drip connection of the main (no F&T trap) does that function as a vent of the main supply or just the dry return.  See photo of the connection.  The vent is hidden by the main but connected to the dry return line that connects to the bottom of the drip connection.  I'm not clear if this should be considered a supply vent or return vent.

Thanks.

gerry gill

bigger radiators generally

require bigger vents, and a main vent on a dry return only services the return piping.

Steamhead

Those capped lines on the drips

tell me there was a crossover trap there. That would let air get from the steam mains to the dry returns, where it would be vented, and close against steam.