Undersized boiler ramifications, venting, and layout

Curious_J

Now that I've replaced my underground wet return that was leaking 100s of gallons a week, I am able to devote more time to figuring out out to maintain/update/optimize my two-pipe Trane vapor system. Mr. Holanan's books and this forum have been absolutely invaluable in understanding things and in dealing with contractors (and knowing who to trust) - thank you!

I've recently done a EDR survey and added up my radiation to 763SF yet my boiler is rated at 629SF. The average temperatures here, in Michigan, have been hovering at about -10°F the previous few days and my boiler has not fired more than about 11 hours - which for a house that is 130 years old with original windows and not a whole lot of insulation, seems pretty decent. This leads me to question if I made a mistake somewhere. All of my radiators are the 2-1/2" Cortos for which I used the standard tube-type EDR tables. Does it make sense that I have an undersized boiler given the above? I've read a lot on here about the implications about an oversized boiler - what ramifications does an undersized boiler have?

I also recently replaced the Trane bullet-type vents on my two steam mains and dry return with Big Mouths. I calculated Steam Main #1 to be .92CF, Steam Main #2 to be 2.41CF, and the radiators (not including runouts and limited to their B1 trap capacity @ 2 oz.) at 9.32CF. I figured one vent on the two steam mains would be adequate but that the return should probably have two. Sound right? For what it's worth, I also replaced my Pressuretrol with a Vaporstat and installed a low-pressure gauge. I have not seen the gauge rise by so much as an ounce (though, I also haven't seen it after the boiler has been firing for an hour).

One last question: I have not been able to figure how my risers make it to the second floor. I have a short section of main, right off of the boiler, that is 3-1/2" pipe before it drops down to 2-1/2" pipe and there is one runout from that thicker section that disappears near the masonry of the chimney. Could this be where things make their way up? From there how would it be distributed? Would there be a vent on that riser (perhaps in the attic)?

Jamie Hall

You may be undersized, but it may not matter -- if the house is heating adequately and reasonably evenly, enjoy. Measuring EDR is a bit of a guess anyway.

On the vents -- you sound like you're on the right track. On any vapour system, it is much more important to get the dry return vents adequate than the steam main vents. If your pressure isn't rising, you may not need to change anything at all.

clammy

Do your end of the supply main drop into a wet return and are your dry returns separately dropped into a wet or do u still have the trane air Elimator in place in to which both dry returns tie into before they drop into the return usually with a check valve arraigement , I have had great luck when removing the air elimator and adding tees and vent and drop into a wet return over the years I ve run into a few varieties of trane system some with all the original details and some which while all original had nothing no traps on convectors no crossover on mains only trane vacuumed vents on the end of mains and dry returns they held vacuume I updated them after 80 years of service w Hoffman 67 vacuum vents and distrubition while under vacuum while system is between cycles and starts to steam is extremely quick . While I know those big mouth vent quickly a thought of return to vapor vacuum maybe worth it .peace and good luck clammy

Curious_J

@clammy
What I have, seems to approximate the diagram below. Not familiar with the Trane Air Eliminator; it isn't the same as the Direct Return Vent Trap, is it?

I'm attaching some pictures as they will likely more clearly explain things than my novice vocabulary, but as I understand it... my supply mains drop into a wet return that, essentially, runs right back to the boiler. However, tied in to that wet return there is the dry return which does have a couple of check valves with the Direct Return Vent Trap in between. The steam line has been removed from the DRVT, so I am assuming that it no longer functions. My radiators have Trane B1 traps - I just bought an infrared thermometer and will be testing those soon.

I had thought about putting in some Hoffman 67 vents but it seemed like the thought here was that it wouldn't be worth the cost and/or it was unlikely that my system was airtight and could hold the vacuum. Aside from the vacuum traps, what else would I need to do to to switch to a vacuum system? What other modifications were you mentioning?

ethicalpaul

Nice looking return fix

clammy

What u have there is a trane return trap n if the float and seat where operational u would need that equalizer line to pressurize the chamber as the water level rises and lifts the float which allows pressure from your equalizer to push the water back past those checks into the boiler if a vaporsta is installed n u run low enough pressure all should be good . If your leaving the return trap and such I would disassembly those checks and flush them out and re assembly if i remember correctly u have traps w no elements possiblably your boilers undersized and
If your boiler piped properly and producing good drysteam and piping is insulated and ur not condensing all that steam in ur mains u may sneer by and not have issue amazingly I have seen it work but the sun moon and stars usually have to aligne I believe you will get it functioning correctly just remember it worked properly at one time just have to unravel the fortune cookie correctly in most cases w older homes when working correctly there nothing that’s as ecomincal as a properly functioning steam system as long as that near boiler piping exceeds the manafactures specs which is usually bs and she is clean and sized properly . Seems like a lot to ask but really is not peace and good luck clammy ps don t be discouraged u will get it and also read study and learn there’s never some trick that makes it all happen and no one just woke up and knew it all it’s a endless quest that should stop at your last breath it s called learning good luck

Curious_J

@ethicalpaul Thanks for the compliment on the return piping. I was impressed and happy with it. The mechanical contractor that did it has an impressive work history behind them with a lot of nice looking and well laid-out commercial work. I knew I was in good hands when the owner whipped out his cell phone and started showing off his company's work.

@clammy I appreciate the info and wholeheartedly agree with your PS... I love learning and the process of learning. The "endless quest" is what makes it so darn fun and rewarding - knowing there are new discoveries to be found, you just have to find them.

You bring up an interesting dichotomy that I don't understand: why would you need the direct return vent on a vapor system? If vapor systems, by definition, run under 1psi which equates to 28 of water in the drip - which is a third its capacity, why would Trane design in a mechanism to deal with water at 3+psi (assuming my math and understanding is correct)?

I have partially disassembled the swing checks and was surprised to see them with hardly any gunk on them and operating freely. I did my best to check their operation and they seem to be working as intended.

Any thoughts on how steam gets from the basement to the second floor? Their don't seem to be individual risers off the main that I can't trace to first floor radiators and no obvious main/primary/mega riser that goes to the second floor unless that is what the runout leads to off of the 3-1/2" portion of supply main.

Jamie Hall

I expect that Trane designed something to handle 3 psi for the same reason Hoffmann designed the differential loop -- in the bad old days of coal, it wasn't always possible to prevent the boiler from getting too enthusiastic and overpressure things. So they designed ways and means of getting around the problem, if and when it happened.