Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Orifice Questions and More

After a few years now on the wall and re-reading all of Dan's books I am still stumped on a few things that I am sure can be answered easily by you experts. Thanks for any time and thoughts:

Here are my system highlights:

2-pipe Mouat vapor system with orifice valves

WM EGH-85 boiler with bad near boiler piping

3.2 CFM at 3oz venting on main (Gorton#2+Hoffman#75)

126ft of 2 1/2" pipe and 38ft of 1 1/2" pipe for mains

1.9 CFM at 3oz venting on return (2x Hoffman#75)

EDR is about right for the boiler

Honeywell FocusPRO 6000 thermostat set to 1 CPH

All but 1 radiator heats well

Believe all traps are failed open

1) Why are orifice valves a good thing? It seems to me that getting the steam into the radiators as quickly as possible would be the best thing to do. I understand the idea that only letting the amount of steam into a radiator that the radiator can condense sounds right, but doesn't that make the cycle times longer and therefore the fuel use greater as you're waiting for the steam to get through the orifice? Of course, running with "wide open" supply valves means the steam traps better be working well (which mine currently do not), but if we assume the steam traps are working should the valves still be used to throttle the steam's entry into the radiator?

2) On the other hand, if we agree that orifice valves are a good thing, and if I can get my valves to only let the right amount of steam into each radiator for a cycle do I need to spend the money to repair my traps? I know that it might be impossible to get each radiator valve fine-tuned that well but if it can be done the traps become unnecessary, right? Or is the money for correctly working traps worth it because they will ensure that any steam that reaches the radiators is not wasted?

3) After the point that my two mains converge they drop down to the wet return so the vertical pipe from the ceiling where the mains run down to where it meets the wet return is very hot (full of steam). Is this wasted steam? It seams to me that the steam running past my mains and therefore not going to my radiators will continue to condense and be replaced by more steam not going to my radiators. The original blueprints for my system show no trap after the mains converge to stop steam from heading to the wet return and there is no evidence of any such device ever being there. Am I paying the fuel company to produce steam that never has a chance to get to my radiators?

4) Thermal images of my radiators show steam entering the supply side of the radiator at the top then heating across the radiator to the far side and then heating down the far side of the radiator. Since my traps are on the far side it seems to me that the trap will feel steam and close (again, if my traps were operational) long before much of the radiator has received steam. Then once that trap is closed, no more steam can enter until the steam currently in that radiator condenses and the trap opens again. At that point, won't the steam take the same path and head to the far side of the radiator again? So, is having the trap on the far side of the radiator a bad idea because it makes much of the radiator unusable? If you look at the thermal picture attached you can see what I mean. If the trap was working correctly on this radiator how would the bottom-left third of the radiator ever get hot?
This discussion has been closed.


It looks like you're new here. If you want to get involved, click one of these buttons!