radiant baseboard zone running off steam boiler - problem with trapped air

wanttolearn

I have a question for the steam experts out there. I am not an expert, so some of my terminology might be wrong:

The main heat in my house is provided by a steam boiler heating steam radiators. There are two rooms however, that needed some additional heat, so the prior owner installed baseboard hot water heaters and connected those baseboards directly to the steam boiler. The hot water from the boiler is circulated by a taco circulator. there is one pipe leaving the boiler, and somewhere down the line it forks into two pipes which have zone valves on them. when the one room calls for heat, the one zone opens up etc. but there is only one pipe leaving the boiler and one returning.

the system does not work the way it is set up, because air keep getting into the baseboard system. I am not sure of exactly why, but based on what I have been reading on this site, this kind of a loop is an "open" loop, not a closed loop, and when the system is idle gravity is causing the water to drop back down in the boiler and air fills the pipes.

There are some tedious ways that i have found that i can force the water back into the loop, but it is a great headache and i dont want to keep doing it anymore.

Now I am getting to my main question: this loop that feeds the baseboard heaters does not have any air purging vents anywhere, it is just a continuous loop. Would a solution to my problem be to install some of these vents throughout the loop so everything air gets into the system it has a way of purging out by itself? or is there something about open loops on the steam boiler that I cant have a purging valve on the loop? If i put in a purging vent, will it disrupt the "tightness" of the open loop and cause the water to fall back into the boiler more easily?

any comment/suggestions would be appreciated.

Jamie Hall

I presume from your comments that these baseboard radiators , (not radiant heat, by the way -- that's very different) are above the water level in the boiler? That makes things a little tricky, however.

First, where does the return from the radiators tie in? It should be tied in to the wet return before the Hartford Loop. If it is, then once you get the piping purged of air it should stay that way -- unless you have a leak (even a very small leak which might not be noticeable) above the water line somewhere, or the intake off the boiler is too high which can also allow air to get in.

If it ties in above the water line that's not good, and there is no easy way to fix the problem. The best solution -- and it's a bit pricey -- is to feed an indirect tank from the boiler, and then run the baseboards and pump as a standard closed loop hot water system, complete with expansion tank using the indirect tank as the water source. Alternatively, if there is an unused domestic hot water loop in the boiler, you can use that -- again with an expansion tank, of course -- as your heat source for a closed loop system.

wanttolearn

like i said, i am not an expert, but as far as i can tell visually both the pipe leaving the boiler and the pipe returning from the boiler are BELOW the water line in the boiler. maybe not by much, but by at least by 4 to 5 inches below the water line, maybe even more than that.

Fred

The pipes at the boiler are below the water line but are the baseboard radiators above the water line, on a first floor or in the basement, where they are also below the water line? If above the water line, you need to configure a closed loop system.

wanttolearn

the baseboards are above the water line. the boiler is in the basement. one baseboard is on the ground floor, the other one on the second floor.

ChicagoCooperator

I take it the piping and radiators that (I assume) were originally in those rooms have been removed? I was going to suggest returning them to steam rather than the hot water.

wanttolearn

the radiators are still there, but i guess they were not enough to the previous owned ADDED basebaord heat.

ChicagoCooperator

So then my question is; are the radiators sufficient? And could they be tweaked so you could abandon the baseboard and it's problem?

ethicalpaul

Fred said:

The pipes at the boiler are below the water line but are the baseboard radiators above the water line, on a first floor or in the basement, where they are also below the water line? If above the water line, you need to configure a closed loop system.

I can't quite tell what you are saying here @Fred and it's complicated so I will attempt to clarify. If this isn't helpful, let me know.

The radiator can be above the water line in an open system. But it can have no leaks or as @Jamie Hall says, air will find a way in.

Also, the supply and return lines must at ALL TIMES be below the water line. There are times, we all know, where the water line of a boiler can vary. I'd be nervous of a line just 4 inches below a given water line.

wanttolearn

but coming back to my original question: would installing an air purge valve solve the problem that air is getting in? or would putting in the valve actually make the problem worse, because you are creating a "leak" in the line?

KC_Jones

wanttolearn said:

but coming back to my original question: would installing an air purge valve solve the problem that air is getting in? or would putting in the valve actually make the problem worse, because you are creating a "leak" in the line?

If you don't have a heat exchanger than you don't want an air purge. You want to view this system like a drinking straw, it needs to be filled up without any air and then the air kept out. IF there is any kind of a tiny leak air will get in and you basically have to start over. It sounds like air is getting in somehow and you need to keep the air out, not look at getting it out once it's in.

https://heatinghelp.com/systems-help-center/how-to-run-a-hot-water-zone-off-a-steam-boiler/

wanttolearn

this is very helpful, thanks. two follow up questions:

how do i spot any small leaks in the line? would i see water dripping out or not necessarily? can leaks we visually detected?

also: along the line i noticed there is one spigot that looks like a typical garden spigot. I presume this was put in to open the line and drain it. of course, the spigot is in the closed position, but could this be the tiny air leak that is causing the system to fail? should i look into removing it from the line?

Grallert

The trick it filling the baseboard loop completely. If there are not leaks and the supply and returns are below the water line and stay that way That loop or loops will work. Keep in mind the water in the boiler is boiling and can flash to steam pretty easily. I've installed a few of these successfully but they have all had a mixing device or piping arrangement of some kind to keep the water loop well below steam temp.

ethicalpaul

The leak (if there is one) can be difficult to find I would think because it is an _intake_ leak into the line of atmospheric air, and those leaks aren't really visible

And the "leak" could be inside the boiler if the water level ever drops below the level of the port (not really a leak, just a problem with the water level getting low enough to let air into the line)

Jamie Hall

I would not say that 4 to 5 inches below the water line in the boiler is enough. As I noted, the return should be to a wet return at or very near floor level; the intake should be as low as possible in the boiler. As to finding small intake leaks... as they say, good luck with that. It's almost impossible, as leaks which leak under vacuum often don't show up under pressure -- and vice versa.

mikeg2015

If installed right, the loop should have isolation valves and two boiler drains on it (hose spigot type valves) so you could isolate the loop and then carefully pressurize it using a washer machine hose connected to a utility sink or the drain valve on a water heater (somewhere with a hose connection).

Other possibility I could see, is of the loop doesn’t turn downward towards the floor once it leaves the boiler (another reason for this) and micro bubbles are traveling up the pipe. Other reason is so pressure is slightly higher where the pump is located to prevent flash steam at the suction of the pump.

BobC

A lot of the new hose bibs these days leak a little, make sure you use good ones.

Bob

ethicalpaul

Correct me if I’m wrong everyone, but isn’t a positive feature of an open loop the built-in ability to clear small incursions of air during pumping?

At least as long as it’s small amounts and there is enough flow rate?

Whereas with a closed loop you’d need an air extractor or bleeder?

I had an atmospheric (open loop) ground source heating system and it would self-purge just by running the pump, no purge station necessary

Jamie Hall

You're not wrong. Problem is, of course, that you have to have enough flow to actually purge the lines, and everything must be in series. Which often isn't the case in heating layouts.