Condensate to boiler feed conversion

AWOL

I have a one pipe steam boiler with two zones. I believe it has multiple piping problems. Once it's up to steam, all the water exits the boiler and it shuts off via the low water cutoff. I've had 4 "plumbers" look at it and shake their heads. Needless to say, I've had to shut off the auto feed and add water via the sight gauge.

I picked up Dan's book and read it several times. The thought is to tackle this in two parts. First- Re-pipe the feed side then Re-pipe the return. I have all summer. the picture below shows the plan for the re-pipe of the feed side.

On the return side, there used to be a condensate pump. It was removed when the pump failed. when it did work, it constantly flooded the boiler. (slow condensate return). Because of the zone valves, I know it needs to be put back.

Finally the question- Can i use the condensate tank as a boiler feed tank? Per my calculations, the boiler has 845sq ft EDR so the receiver size should be 10 gallons. The condensate tank has 9 gal capacity.

Jamie Hall

There's something...

about this... the arrangement of the zone valves bothers me.  I'm not sure I'm on the right track -- I've been known to be out in left field before -- but I presume the drip returns from the steam lines to the return are on the far (downstream) side of the zone valves?  If so, and the valve closes, it seems to me that it just makes sense that the steam in the boiler while happily push the water out of the boiler and into the part of the system where the zone valve is closed.  Where it will stay, until either the boiler shuts off or the zone valve opens.  Not saying that this is all the problem with slow return, but it could be part of it.  I'd really like to see a sketch of the whole system, vents and all, as it stands... if possible.

Steamhead

You might have something, Jamie

My question is, what type of boiler is this, and does it have 2-stage firing? 

gerry gill

Is this a residential boiler?

Doesn't sound big from that EDR...so why is there a pumped return...why not gravity.

AWOL

Current feed and return piping

The boiler is a Hydrotherm PB-235. It does have two stage firing and shut down.

Here are pictures of the current system. I have more if something is missing.

AWOL

Zone valves

Because the system has zone valves, it should have a condensate pump or boiler feed pump. Is that not true?

The Steam Whisperer (Formerly Boilerpro)

Some problems

The Traps at the ends of the mains are probably causing most of the issues.  Also, the water probably returns slowly because there is no air venting for the mains...especially now with no pump....or way too little with a pump.  Typical traps do not vent air adequately for good system operation..especially in one pipe because of the larger venting needs.   If you move the steam through the system quickly to the ends of the mains, the condensate will reach the end of the main much sooner.  Also, with so little venting, whenever a zone valve shuts off, that branch will go into vacuum pulling water out of the boiler into the steam main.   The radiator vents are just too small to act as good vacumn breakers.   Getting rid of the traps, installing proper main vents, and making sure the system runs at very low pressure  (probably under 1 psi)  so the water can't get too high in the off return when another zone is on should get everything running properly.   Assuming everything else on the system is working properly.....

Steamhead

Not necessarily

if you can keep the pressure below the "B" dimension, gravity return should work. 

Dave in QCA

Can we see the return piping?

Would it be possible to see more of the return piping?  Does the piping go to a receiver or directly back to the boiler?  Are there any kind of check valves in the return piping, and if so, where are they located.  Is there a condition in the building that actually requires the zone valves?  What pressure does the boiler operate at?  Does the boiler maintain pressure all the time, or does it only fire when a zone valve is open?

AWOL

More information

This is a two family house. Each floor is on it's own zone.

The piping goes directly back to the boiler. The picture on the left is from the return end of the mains back to the boiler. There are no check valves, only the traps. I intend on adding main vents before the traps. The is no check valve on the return.The boiler is running at 1/2 lb. The boiler only kicks on if a zone valve opens.

Dave in QCA

Thanks for more information

OK.  Thanks for the information. 

I suspect that your boiler may be getting to a higher pressure than 8 oz.  A pressure of 1 pound would be capable of lifting a 27" column of water, and your return main looks pretty darned low in comparison to the water line of your boiler.  If your boiler had a pressure of 1 pound, had one zone open and the other zone closed, the closed zone would have a 0 pressure.  It would not be in vacuum because the vents in the radiators would relieve any vacuum.  Of course, there could be a brief period of time when a fully heated zone shut off that the vacuum in the zone could suck the water out of the boiler.  Assuming that the boiler pressure is getting a little higher than you think, there is probably enough pressure to lift the water to the height of the end of the steam main, and thereby floodin the main and pushing water out of the boiler.  By the way, that little vent by the steam riser is not needed.  It is intended as and air vent if the boiler was set up for water, but for steam, you need to remove it and cap the line.  You also need to remove the 2 main F&T traps.  They would serve a purpose if you were returning to a vented receiver.  In that case they would provide venting ability, albeit poor, and would prevent steam from entering the receiver tank.  Since you are returning to the boiler, venting is not possible, you must add a main vent to the end of each main.  I would also recommend that you change the piping so that each main drops to the floor level, then, in each wet return line, in horizontal orientation, install a high quality swing check valve.  After the check valves, you can bring the lines together before they proceed up to the hartford loop connection in you equalizer line.

You also really need a pressure gauge that reads in ounces (unless that is already what you have) and a vaporstat instead of a the common pressure switche that is usually suppied with steam boilers. This will allow the boiler run a very low vapor pressures and reduce the pressure differential that is causing the water to be pushed out of the boiler.  In the event that the pressure does exceed the water column height that you have, (difference between your boiler water line and the height of the return end of your main), then the check valves should serve to prevent backward flow in your wet returns.

I would also recommend that you take a look at the installation manual for this boiler.  I think that I can see and equalizer in your piping set up, and it sure looks like 3/4 copper.  The installation manual should calls out the minimum allowable size for this boiler as 1 1/4".  It shows the steam supplly piping leaving the boiler at 2".  I will attach a pdf file of the installation manual.

I am surprised that in the effort to create individual control in this 2 family building, that someone didn't simply install 2 boilers and have the occupants pay their own heat bill.

Anyway, I hope this helps and would like to know how it all turns out.