Is my boiler oversized?

Roddy

My boiler is probably about 40 years old. Weil McLain, single pipe steam, parallel system and it works well with professional occasional maintenance and regular maintenance by me, the homeowner----no complaints. I have no intention of replacing it if/until I absolutely have to. That being said, I have a question. I live in the Chicago area and we recently had record breaking low temperatures. My stat tracks running time of my boiler, and even on these recent bone chilling days, the most my boiler ran was about 12-13 hours in a 24 hour period. Would that indicate to you that it's oversized? Just wondering in case I ever have to have it replaced.

Fred

That really doesn't suggest anything. We know nothing about the windows, upgrades to the envelope, if you live in a single family home or multi-unit, etc. The only real way to determine the size of your boiler, relative to its connected EDR is to measure and total all the Radiator EDR and compare that to the Sq. Ft. of steam output on the boiler plate. If they match or are close, the boiler is properly sized. If those numbers are way off and the output of the boiler is much larger, then the boiler is over sized. Another indicator, although not an accurate measure, is to watch the boiler and see if, at some point during a normal heating cycle, the boiler starts to short cycle, (on two or three minutes, off a couple minutes, then back on again until the thermostat is satisfied). That would indicate the boiler is putting out more steam than the radiators can condense at any given time.

Jamie Hall

Actually, @Fred 's second method, while not seeming to be as accurate, is an excellent approach. Not only can you determine whether the boiler is oversized -- but you can determine by how much, if it is. If you find that it does, in fact, cycle on pressure, time the cycles over a number of them. The percent oversize is given by the ratio of the average total cycle length, from start to start, divided by the average on time, from when the boiler fires to when the pressure switch cuts it off. In my humble opinion (others may beg to differ), anything between 1.1 and 1.3 is just fine. Much less than 1.1 and the system may be a bit slow getting heat to all of the radiation -- venting or no venting. Anything much over 1.3 is probably excessive.

Roddy

Thanks Fred and Jamie for your comments. I understand what you're saying.

I'd like to mention that my system rarely builds pressure at the pig tail that shows at the pressure gauge, so it almost never cycles off due to pressure. The stat is satisfied before it would cycle off. Rooms heat fine, etc. The only time it cycles due to pressure is when/if I raise the temp at the stat by a couple degrees, which I usually only due at the beginning of the heating season to check systems, etc.

Again, thanks, and I'll keep all of this in mind if the day comes that I have to replace the boiler.

gfrbrookline

@Jamie Hall and @Fred it is nice to see you two agreeing instead of sparing. You are both very knowledgeable and with steam there can always be multiple solutions for the same problem.

Fred

@gfrbrookline , I don't think we spar very often, if at all??? Maybe I'm not paying attention or just know when trying to diagnose a problem, from afar, everybody's input offers a different piece to the puzzle, each taken as constructively working towards a solution. I hope @Jamie Hall doesn't think my intent is to spar. He knows way more than I do!

Gilmorrie

Quit worrying. If the boiler is heating the house, fine. Actually, there are some benefits to an oversized boiler.

Phil53

Where in the Chicago area are you? I'm in Aurora

Jamie Hall

Fred said:

@gfrbrookline , I don't think we spar very often, if at all??? Maybe I'm not paying attention or just know when trying to diagnose a problem, from afar, everybody's input offers a different piece to the puzzle, each taken as constructively working towards a solution. I hope @Jamie Hall doesn't think my intent is to spar. He knows way more than I do!

Heavens no, @Fred -- we do differ, now and then, but not by that much -- certainly wouldn't have called it sparring! -- and I thoroughly enjoy your viewpoints -- and dialogue!

gfrbrookline

@Fred and @Jamie Hall perhaps spar was too strong of a term. I actually enjoy your back and forth with different approaches to the same problem. You both have great knowledge but look at things differently. Like many things in life there is not always only one correct solution for a problem. That's what makes this site such a great resource to home owners and building managers like me. As an example I have an old Honeywell round tstat in my place in RI and a VisionPro 8000 in my condo building in Boston. Both work great.

Roddy

Phil53 said:

Where in the Chicago area are you? I'm in Aurora

I'm in Joliet, in the Old Cathedral area. Are you a professional, Phil?

Phil53

No, not a pro just interested in steam systems and old homes. Thought if you were close enough I could stop by and check it out if it was OK with you.

Motorapido

Gilmorrie said:

Quit worrying. If the boiler is heating the house, fine. Actually, there are some benefits to an oversized boiler.

What could be the benefits of an oversized boiler? So many of us spend so much time worrying about our oversized boilers that it would help put a smile on our faces if you tell us what are the benefits of an oversized boiler. I need a smile on this snowy morning.

Gsmith

will heat your house on days when the temperature is below the design day. Remember even "properly" sized boilers are oversized on all days warmer than the design day in your area, which is almost all days.

ethicalpaul

Also, you can add a hot water zone without worrying about the size.