Correcting sloppy work...?

Julan

Heya,



My building has a one-pipe system. At some point in the past (60's, 70's) when the exterior porches were enclosed and amalgamated into the rest of the living space someone (likely not a heating contractor) decided to run a branch from the main pipe to the back room so that new radiators could be installed.



I have noticed that the rear room radiators only get moderately hot at the end of the heating cycle and as such don't really provide enough heat to the room.



I followed the piping in the basement and I think I've found the problem:

The main pipe is 6" and the branch is 2". Instead of tapping into the main pipe at the top of the pipe (like all the other original branches do) thus allowing the steam to easily rise into the new branch they tapped the side of the main pipe. My belief is that the steam doesn't naturally want to make a 90 degree turn into the new branch and only fills it up when there's nowhere left to go at the end of the cycle when all the other radiators are full...



I was wondering if closing up that branch and re-tapping the main pipe at its top would provide a better path for the steam?

Jamie Hall

Might help...

on the other hand, there are a few other possibilities which might also be considered.



First, I don't happen to have my copy of Lost Art handy, but I would add up the radiation served by that 2" runout, and check it's pitch and length, and then determine if the pipe is big enough for the job.  It just might not be. 



Second, I would check the venting; if that runout is much longer than say 5 to 10 feet, it's really more like a main -- and would benefit from having a good vent at the end of it. 



Third, if that pipe isn't insulated, insulate it.  That will help a lot...

Hap_Hazzard

They probably need more venting.

First, when you give the pipe sizes as 6" and 3", I assume you are measuring the circumference? If that's the case, the main is 2" and the runout to the rear radiator is ¾".



¾" is too small for a radiator runout, but it's probably not directly responsible for the slow heating. Unfortunately, if you fix that problem, you'll see why ¾" is too small for a radiator runout. Is there any possibility you can replace the ¾" pipe with a 1" pipe?



My guess is that they used a ¾" pipe because the fitting they used was originally where the main vent was located. ¾" is the standard thread size for a main vent, and it's not unusual to find extra radiators plumbed into former main vent fittings in the mistaken belief that the radiator venting will adequately vent the main. Unfortunately it doesn't work.



If you want to try something cheap that might improve the situation, try putting a Gorton #1 on the rear radiator and see if it heats any faster. If it does you may notice some water hammer and/or water spitting out the vent. If it doesn't you could try putting smaller vents on some of the other radiators, but this will increase the system pressure.



The long-term fix is to re-pipe the runout and add a main vent.

Jamie Hall

Good heavens...

Hap, I'm slipping.  Not enough coffee or something.  Thank you.  If the "main" is said to be 6", it's either a huge house -- or as you say the circumference of a 2".  Much more likely.  In which case you're absolutely right; that's probably a 3/4 " runout.  Which is WAY too small.  An inch might be better, but it really should be at least 1 1/4 or 1 1/2.



Better venting on the radiator might help, as you suggest -- but I'd be rather worried about getting some water hammer in there through the whole cycle, unless it's pitched really steeply.

gerry gill

As the guys said,

pipe size, load, insulation, and i'll add is the pipe a counterflow or parallel flow line? that makes a huge difference.

Hap_Hazzard

I think I'm slipping a little too.

I thought he said the runout was 3", which would be the circumference of a 3/4" pipe, but now I see that he said it was 2", which would be the circumference of a 3/8" pipe, so now I don't know what to think. I doubt it's actually either 2" pipe or 3/8", but who knows. I think we need to ask him to check it again.



But, yeah, if it's 3/4" and he fixes the venting it's probably going to hammer. Once it starts heating better it's going to produce more condensate, and it remains to be seen if the runout can accommodate it. That's the trouble with these situations--sometimes fixing the obvious problem just allows the next one to manifest.



Then again, maybe that 2" is the OD, which would make it a 1 1/2" pipe, and if he puts a bigger vent on the radiator it'll work like a champ. I hope so.