Boiler Water loss--How much is normal

Dave in QCA

I feel a little bit silly in floating this out here, but I've change my boiler operating habits and I'm seeing something that causes me concern.

Back in December 2012, we installed a new Weil-Mclain 680 boiler. There was a very detailed post about that project on here at that time. The system is a 2-pipe Dunham and the venting is through a pair of Dunham Air Eliminators and both have air checks on them. After a steam cycle, the system goes into vacuum and it holds well. At 1 cycle per hour, there is not a discernable loss of vacuum. However, if there is not a call for heat, the vacuum will dissipate before 2 hours passes. So, the system is not 100% tight, but is pretty darned tight. There is no underground returning piping. All of the basement piping is visible with steam lines insulated. There are no leaking radiators, no leaking traps or inlet valves. There is no visible leaks in the boiler and there is no white smoke. So, this sounds like a very tight system, right?

A change in my LWCO blow-downs has caused me to question it. In the past, I have flushed the 2 MM LWCO devices and have also done a quick flush of the drain. The boiler has been treated with SteamMaster tablets from the beginning. I catch the blowdown water in a bucket and it is always very clean. When I flush the LWCOs, I always manually top the boiler off to the normal water lever, using the bypass on the autofill meter (VXT) Each fall, at the beginning of the heating system, I drain the boiler and wand out the bottom, refill, add Steammaster tablets, and bring it up to steaming for 15 minutes.

So, this year, rather flush out clean water and cause the treatment to be diluted, I cut back on the blowdown routine. I waited until Thanksgiving to for the first blowdown, and it was perfectly clean. So, I waited until February 1 for the next. What I noticed was that I was beginning to see water use on the VXT meter. I did one more blowdown at April 1, and again, the water was clear. However, now, at the end of the season, the VXT is showing 36 gallons used. The boiler holds around 50 gallons as I recall. The only place that I can identify that water is lost, is in the humid air that is expelled in the venting oz.

Your thoughts and insight would be greatly appreciated.

EBEBRATT-Ed

Not sure If I understand but in previous years you filled manually after blow down and this year you let the feeder do it??

So now your seeing 36 gallons and wonder if that is too much??

It's like 70% of what the boiler holds I don't think it's an issue. Probably lost through the vents

Dave in QCA

To Clarify, in previous years I blew down every 2 weeks and manually topped of the water level. THIS year, I only blew down 3 times total. As before, I manually topped off the water level.

Jamie Hall

Does that 36 gallons include the blowdown use? If the system still holds a vacuum -- and two hours isn't half bad for that! -- I'd not worry about a leak, and it may possibly be just humid air being lost. However, if it no longer holds the vacuum, I'd go looking for a tiny drip somewhere -- most likely spot is, oddly, in a dry return at or near a fitting.

JUGHNE

Previously when you manually topped off the boiler was that water recorded on the VXT using the switch?
Or the valve bypass around the VXT?

Dave in QCA

Jamie, 36 gallons does not include the blowdown use.

Dave in QCA

JUGHNE said:

Previously when you manually topped off the boiler was that water recorded on the VXT using the switch?
Or the valve bypass around the VXT?

It was done with the bypass, so that was never recorded in the past. I probably topped it off higher than the NWL and often enough to mask the normal water loss. However, because of that, I don't have a clue what the normal water loss is.

PMJ

36 gallons (on top of blow down water) escaping a natural vacuum system performing as you describe as humid air through vacuum vents which would be rarely be open is unlikely.

If the system really holds vacuum like you say (mine is very similar) I would have to shut off the supply valve and observe for myself the sight glass and the VXT for every add to satisfy myself about the number it was coming up with.

dopey27177

In a new heating system a bout your size 1 gallon per month water loss is normal.

In a system your age 3 gallons a month would be normal

Because you lose all your vacuum in two hours your system is not as tight as it could be.

My guess is you have slight leaks at packing glands of the radiator valves and other valves.

As far as the as vacuum loss, check the air check or penny valve for dirt on the seats, this could be the vapor loss (water loss) and system vacuum loss.

Jake