Should I increase pipe size?

Oradaps

I was called out for a "no heat in two radiators". Here's what i found. 40-50's era house with 2 pipe steam. The 2 radiators with no heat were in an addition that was built about 30 years ago. According to the homeowner they have never heated. The rest of the rads. in the original part of the house heat fine...well, they get warm. The system has a hodgepodge of hot water rads. (still with the bleeder in) rads. with air vents (remember 2 pipe) and not a steam trap in sight. No F&T as well. There is one main vent on the return. (just painting the picture). Back to the problem rads. They are fed by a 3/4" supply off of a 2" main (near the header). The 3/4 line runs 10' into a crawl space and then tees into 1/2" and go 20' to the left for one rad. and 20'to the right for the other. The returns run parallel with the supply. Grade is good now. Which i thought was the original problem, there were some bellies in the pipe due to poor strapping.After regrading, still no heat. I ran the boiler for an hour with returns disconnected at unions and didn't get a whiff of steam or air. Checked the valves and rads. to make sure they weren't stopped up, they were fine. Here's what i'm proposing to do, increase the supply piping to the problem rads. and install steam traps on every rad. Okay I think that's it. Would love to hear what you fine folks think.

Ironman

I'm thinking that if nothing comes out with the returns disconnected, then enlarging the supply isn't gonna change that unless the supply lines are plugged.
Did you try disconnecting the supply at the unions? Keeping working back toward the supply main until you find the problem.

KC_Jones

I am just guessing here, but if there is a single 3/4" line reduced down to 2- 1/2" pipes the resistance to steam flow is so high the steam might not go there. Especially if it has other less restrictive options. Those are tiny pipes for a steam system especially with runs that long. I know it's 2 pipe which can take smaller sizes, but with the admitted hodgepodge of piping and air vents etc. it sounds like a total mess. You say 2 pipe, but no traps. Could this be a 2 pipe air vent system? If so functionally it's more like a 1 pipe system isn't it? If that's true then the pipe size is definitely too small. I agree with Ironman there needs to be more exploration to figure out where the steam stops. Can you tell by feeling the pipes how far the steam is getting with everything hooked up? Are those pipes in the crawl space insulated? If they aren't insulated could the steam be condensing in those pipes at a rate such that the steam just never gets to the end before the thermostat kicks the boiler off? Ton of different possibilities. Boggles my mind that they have never heated for 30 years and no one has ever wanted to do anything about it?!

Oradaps

Ironman, I did take apart the unions on the supply side as well, the steam eventually came, but it had to run for about 20 min (sorry for leaving that out). When I got it on the supply I connected the unions and had my coworker disconnect the return, and didn't get anything. Valves were open, and not stopped rads. As well. The steam evntually came back through the return from the main return.

KC JONES (great name btw) yes I walked into a total mess. First I have never heard of or seen a 2 pipe air vent system. Would like to hear more about that. Second, the pipes are not insulated, and they also have forced air in the addition, the rads. Act as suppliment heat I guess. My boss thought the same about the insulation at first, but after holding on the pipe for about an hr (before disconnecting the supply unions) I dont think the steam ever made in the supply. Like you said it's got easier places to go. And there have been multiple contractors who have worked for this customer.

Oradaps

And thanks for taking the time fellas

Ironman

Oradaps said:

"First I have never heard of or seen a 2 pipe air vent system. Would like to hear more about that."

Here's an article about them from right here on HeatingHelp:

https://heatinghelp.com/systems-help-center/two-pipe-air-vent-steam-heating/

Oradaps

KC Jones , I think your on to something, all of the existing rads are piped like a 2 pipe vent system. As opposed to a trapped 2 pipe system that has the supply pipe on the upper portion of the rad. And a trap on the lower.Ironman thanks for the link. Im not sure if I read that section in DH's lost art. I'm going to dig a little deeper.

vaporvac

Perhaps some pics might help. There are actually two-pipe vapor systems that use upper and lower tapping, but also no traps. They work with a metered valve or orifices. It's best to see exactly what you've got. Maybe some pics of the boiler piping and boiler room, as well

Jamie Hall

And back to the original question... I can't see any way, even if everything else is correct, that a 3/4 inch runout that long is going to work, so yes -- I expect you need to increase the pipe size. I'd say off hand inch and a quarter, but I'd have to look it up.

Oradaps

Vaporvac, the two problem radiators did not have orifices and the valves were fully open. We did pull out a hoffman 76 off of the main return, which the manufacturer says is for a 1 pipe vacuum system. We replaced it with a 75 after our initial call, thinking that venting was the problem. The original part of the house still heats. And sorry no pics as of now.

Oradaps

Thanks Jamie, that's what we're thinking, 1 1/4 into the crawlspace and then 1" to the rads. Leaving the 1/2 returns in place. I'm thinking traps are not a good idea since this 2 pipe vent system has enlightened me a bit.

Oradaps

Just following up, because i know you guys hadn't slept. haha. We increased the pipe size to 1 1/4 to the problem rads and tee'd off and ran 1" to each rad. Wouldn't you know it...they got hot. Left the rest of the system alone. Did not put in any steam traps. Thanks for the input fellas. And KC Jones thanks again for introducing me to a 2 pipe vent system...even my grandfather has not seen that and he's one of those old timers.

KC_Jones

And doesn't it feel good to know you are the first person in 30 years to get them to work?! Good work I bet you just made a customer for life!

Abracadabra

Oradaps said:

Just following up, because i know you guys hadn't slept. haha. We increased the pipe size to 1 1/4 to the problem rads and tee'd off and ran 1" to each rad. Wouldn't you know it...they got hot. Left the rest of the system alone. Did not put in any steam traps. Thanks for the input fellas. And KC Jones thanks again for introducing me to a 2 pipe vent system...even my grandfather has not seen that and he's one of those old timers.

I guess even some Dead Men made some mistakes ;-)