Main Vents with a Condensate Pump

Jim Snave

Just to help understand magnitude of problem. It takes about 18 minutes for the steam to reach the end of the main which has the vent. I am reading that it should only take a couple of minutes. Clearly, there could be large gas savings if it is that far off.

Jim Snave

New Project with Old Problems

I have a 1916, 71 apartment building with a one-pipe steam heating system. I came on a year ago and the first year had crises more serious than the heat to deal with. In 1990, a new boiler was put in and in 1996 a condensate tank/boiler feed-pump was added. The building heating is very uneven. Most apartments are overheated and a few are too cold. The gas bills are huge.

I've been trying to trace the problems and trying to set aside any notion that the system was properly installed in 1996. For example, I have reason to believe that they did not initially install any steam traps when the condensate tank was added. Now there are steam traps at the end of all the mains/on the returns.

My starting point was the Heat-Timer. It turned out to have been set on the District Steam Heat setting for 14 minutes each hour -- it ignored the heat sensor. We calibrated the HSS for the furthest apartment on the longest main, but that main has a vent on it. Of course, now the complaints about heat have grown because it is colder than it was.

All of the mains have steam traps leading down to return piping that is on or below the floor. (It does go down and come back up in places). In the boiler room, the return piping drops down maybe 18" then comes up to reach the condensate tank. The tank is regularly full. I think this piping is problem #1. Air can't get out through the condensate tank air vent because the pipes are full of water.

As I said, the tank is regularly completely full of water. In fact, at the start of the heating season we drained water from the return main for nearly 30 minutes before it went dry. (Water had started to drip out of the air vent on the condensate tank). I think problem #2 relates to our low-water safeties. The boiler has three low water safeties. One is tied to the condensate tank, one can draw feed water directly in. The condensate tank has a feed water connection that includes a pressure reducing valve. However, the current boiler mechanics have the water supply to this shut off. (They thought it was leaking over the summer and that was why my system was full of water. I think the system was full of water for another reason.) I am thinking that the boiler is putting a call for feed water to the direct connection first and then to the condensate tank pump. The result is that we are continually gaining water in the system. The mechanics solution was to shut the feeder to the pump. I am thinking they need to adjust the settings on the low water sensors so the condensate tank pump is called first.

So, we are into heating season and we think our boiler room return piping is wrong and our LWCOs are messed up. Basically, the return piping may be appropriate for a gravity system but is not appropriate for the pump configuration. Can we add main vents on all the mains as a "quick fix" even though there is a pump sitting at the end of the piping and we have F&T traps at the ends? We can temporarily handle the overflow through more frequent blowdowns on the tank. Also, is there any hope of returning our building to gravity operation? (The presence of the pump requires a costly daily mechanical visit which from my perspective is worthless given the state of things.)

My thought is that by adding the main vents to the system, the building will at least heat more evenly, the radiator air vents will stop hissing, and we can spend time thinking about hiring a mechanical engineer to either redesign the return piping or configure a system that doesn't require a pump.

Last night I responded to another desperate heating call about how cold it was. I replaced the Hoffman #40 with a Dole 1A vent on his radiator. It sounds like a tea kettle with the air rushing out, but at least now some of his radiator fins heat before the boiler shuts down. (He is the last apartment on the longest main, but the main with the air vent). Help!

Any thoughts? Thank you!

Steamhead

You definitely need to vent those mains

but the condensate not returning is another problem.

In order to ascertain which vents to use, we need to know how much air is in each main. Then we can size the main vents so they will release air at a rate that will get the steam to the ends of the mains in about a minute (measured from the time the boiler starts producing steam). It's not uncommon to have to build a "tree" of piping to install the number of vents needed on each main.

Dan has included sizing charts in the workbook that comes with his "Dead Men's Steam School" video. It's well worth the price of admission- Dan does an excellent job presenting the material. Order yours on the Books and More page of this site.

The condensate problem may be caused by a vacuum building up when the F&T traps close, keeping the condensate from draining. If there's a union on the trap outlet, loosen it. If air rushes in and water drains out, you've found the problem. The solution is to install one of the main vents for that main AFTER the F&T trap. An F&T trap will pass air which will go out the vent, but if the vent is closed for some reason, it will open if a vacuum forms.

I wonder if that boiler-feed pump is really necessary. If, after properly venting the system, it will heat completely without the boiler shutting down on low water, the pump probably isn't needed.

Let us know how you do!

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