confused on steam pressure

Snowmelt

I am confused on a statement that my local supply house gave me. the supply house told me if I don't make pressure that means the boiler is too small.
I would agree with the local supply house if the thermostat doesn't make temperature.
before we go any further this is the boiler that I am missing between 15 and 20 gallons a day. which is a lot better then the 600 gallons a day it used to use before I replaced it.

Steamhead

Not necessarily. Do all the rads heat up completely after the boiler has run an hour or so?

ratio

It's more accurate to say that if it does make pressure, it's making more steam than is necessary, at that moment.

Too small is one reason for a lack of pressure, but you really need more information to know for sure.

Snowmelt

here is where it gets a little complicated. it has 2 zone valves that the stem is frozen. I replaced the smaller 2 inch zone valve and for theory purposes I pulled the stem out to shut 1/2 the building down. the answer is yes the 4 rads and the air / HEX gets hot. I am working on the other zone valve which is 4 inch , the stem is frozen so I couldn't push the stem in. I am going to get a rebuild kit for that zone.
when both zones are open the 2 inch takes a lot longer to heat up then the 4 inch zone. the 2nd zone will get hot but without the zone valve working on the 4 inch steam pipe, the 4 inch zone will get to 74 degrees while the zone with the smaller 2 inch will only het to 65. but if I keep the heat on I did have it to 70 degrees.

Steamhead

First, fix the zone valves. Then make sure your mains and returns are properly vented. Also, are both zone valves the same type, and how do they correspond with the steam main sizes?

Snowmelt

I do have a condensation pump on one zone . someone told me that the venting is not that critical because of the pump. I didn't believe him but at this rate i'm taking any and all advice.

EBEBRATT-Ed

Steam is going to take the path of least resistance and go to the larger zone when it is open.

You can probably get the zones to heat evenly by venting at different rates.

CantabHeat

In the ideal setup everything gets steam and you barely build any pressure... maybe just an ounce or two. Anything over that in most smaller setups and the pressure is basically saying you are making more steam than the system can consume at that moment. In a finely tuned system you’ll barely see any pressure until perhaps the end of the cycle when most the vents have closed. I’ve seen many systems where rooms have oversized radiators where except for the coldest days of the year many radiator vents never even close and the whole cycle never gets above ~2 ounces of pressure at the boiler. Those systems are very quiet and most never even notice the boiler is firing apart from a few light pings from the expanding metal in the radiators.

Most contractors I’ve come across still don’t understand how these systems work and seem to be of the opinion that it’s some sort of pneumatic system like a locomotive where the boiler needs to be hotter than the blazes of hell and steam blasts it’s way though the pipes under pressure. Of course al that does is lead to the sort of banging, clanging and hissing that gives steam heat a bad name.

Snowmelt

I’m thinking the same way the last post thinks, it’s well over 200 feet of 4 inch pipe and another 300 at 2 inch pipe, so it’s a lot of piping. So it’s a lot of pipe to balance , but that what the zone valves are for.

ethicalpaul

I’m not sure that’s what the zone valves are for. Can you modulate with them? I’m ignorant but interested. I would think they can only be all-on or all-off (to shut down a zone)

In my mind if both mains are well vented, they should both fill with steam before any radiator gets much if any steam. Then radiator venting and length/size of runouts will determine what rads get hot first.

How would a condensate pump remove the need of a main vent??

Pumpguy

Typically, condensate pump receiver tanks are vented to atmosphere, so that's where the venting takes place.

ethicalpaul

Thanks @Pumpguy !

JUGHNE

For a cond pump to vent the air it needs a working F&T trap ahead of it. (Just about always).

Pumpguy

@JUGHNE, Are you referring to a "master trap"? If yes, that's a NO, NO.

See attached file for typical condensate pump installation piping showing air vent to atmosphere pipe .

JUGHNE

Pumpguy, I am referring to the F&T at the end of a steam main which would then vent the main and allow cond water to flow back to the cond pump.
All rads connected should have their own trap to keep steam out of the dry return.
IIRC, the "Master trap" was a knuckle-head job to "fix" open rad traps to keep steam out of the pump. It would probably do that but leave steam in the dry return to affect other rad traps.

I have added main line venting just ahead of the end of main F&T because of length back to the pump, also because of buried dry returns that had sags because of bad replacement practices.

Snowmelt, have you located the end of steam main F&T for the zone that has the cond pump??
I did find one in a closed up pipe tunnel that was severely leaking.....probably losing as much water as the situation you have now. It could be hiding some where leaking and perhaps spewing steam resulting in low pressure on the system.