How fast should steam main fill? My results within

JeffBrown

Afternoon all,

Just doing some maintenance on my 95 year old single pipe system. Small house 1350 sq ft and about 195 sq ft of radiator. Boiler is a 7 year old Weilmclain SGO-3 with a carlin ez gas conversion burner. Timed firing rate about 110-115k btu

Boiler maintains 140 degrees for the hot water coil. I timed how long it took from when the flame lights to when the steam makes it to the single main vent. Vent is a gorton #2 and I'd estimate about 30 feet of main, just 1 pipe making a small rectangle around the interior of the basement. Changes from 3" to 2" after about 30% around. Near boiler piping is to spec.

Anyway, it took 11min 40sec from flame on to steam hitting the vent. I meant to time how long it took to produce steam but I forgot, and ultimately it probably doesn't matter since I'm not planning on changing anything that would make that part faster.

Curious how this compares to others? Should I add another #2 vent to the main?

jeff

Jamie Hall

You really need to start your timing from when the header for the boiler gets to steam temperature. Otherwise, you're not accounting for how long it takes to raise steam.

JeffBrown

ask and ye shall receive....

time from firing to steam in the header: 5min 30sec

time to fill main: 5min

jeff

KC_Jones

Are your mains fully insulated? If yes how thick is the insulation?

Jamie Hall

Strikes me as a bit long, perhaps -- but there are so many variables. It's not outrageous (it takes about 7 minutes for the system I care for, but the mains are about twice as long)(that's from a pretty cool start which makes a big difference, as @Hatterasguy said. And I do mean cool: the basement where the mains are runs around 40 in this weather!)(and yes, the mains are insulated).

nicholas bonham-carter

You could time the steam arrival time again with the main vents removed, and see what difference that makes. Just be ready to switch off the boiler as steam appears at the tapping. If there is a big difference, you may need more main venting, on an antler.--NBC

Gsmith

Seems like too long, I'd add more main venting. For example, just a few minutes ago I timed the steam arrival on my 150k btu/hr boiler with two 2-1/2" insulated steam mains, one 20 feet long and the other 30 feet long:
2.5 minutes for boiler to make steam till the boiler header was too hot to touch.
2.25 minutes from header hot to short main too hot to touch at the main vent.
2.5 minutes from header hot to longer main too hot to touch.
My steam mains have one B&J Big mouth vent on each, my basement is roughly 65 degrees here in New Jersey.

But, does it make economic sense? Hard to say. if you are running 1 steam cycle per hour, typical on many days during the heating season, that 2.5 minutes extra boiler burning time (your 5 minutes minus my 2.5 minutes) means 24 times 2.5 or 60 minutes of boiler burning and gas using time. In my case that would be 150,000 btu's per day (roughly). My gas utility company charges me $8.25 per million btu's (all in, gas plus delivery, etc), so the extra time of 2.5 minutes per cycle would cost me $1.24 per day. Your gas use and cost will probably be different, but you might be able to figure out the payback period for new vents and decide. In my case I had no real main vents (just an old radiator vent pretending to be a main vent) and I figured adding real main vents would be about a 1 year payback. As they say, your mileage may vary. And, insulated or uninsulated steam mains also play a role, uninsulated mains will take longer to heat, they take more btu's to get the steel hot (from a lower starting temperature than insulated mains) and also radiate some of the steam's energy into the basement before the entire main gets hot. Insulation is cheap and usually a pretty rapid payback.

JeffBrown

Morning, and thanks for all the thoughtful responses.

To answer everyone's questions:

1) Mains are insulated with home depot fiberglass, so what is that .75" thick with the paper exterior

2) I ran another test this morning and the pipes cool to the touch. Time to fill header was the usual 5minutes and 30 seconds.

With this new test I removed my main vent so it's an unobstructed 1/2" hole. Time to fill mains without the vent is 4minutes and 32seconds. Compared to my last test with the vent installed that is a time savings of about 35 seconds. So basically time to fill main is about the same with and without the vent. Hmm! Good thing I didn't already order another Gorton #2

How do we explain this? Is the boiler making too little steam too slowly? I imagine if my main was partially obstructed I would get crazy hammering, but system is totally quiet.

Maybe next time I should turn all my radiator vents upside down and try again?

--jeff

Gsmith

Sounds like you have done an actual test on your system that shows additional main vents on your system would not make much difference. So if your system is working well otherwise, no change in venting seem needed.

Reinvent

HD insulation is 1/2" and is crap. Frequently the wall thickness deviates to something less. You should have at least 1" or even 1 1/2" You can leave what you have and add 1" on top of it. You need to locate an industrial supplier of insulation like General Insulation or a similar company.
Also try Nicholas suggestion.

Abracadabra

What's the water level in the sight glass doing during firing? Stable?

Fred

You have a 1/2" tapping into your main(s). I'm betting @Gary Smith has a 3/4" or 1" tapping. You can't get any faster venting than the tapping will allow, unless you change the size of the tapping. I think you are fine.