is it true commercial steam boilers are only apx 80 % efficent

M Ransley

I have a kewanee steam boiler in a 12 unit bldg, ive been told its 65% efficent and new units are only 80% , is this true, and are there any ways to increase the efficency of my old Kewanee

DanHolohan

Well, maybe a bit higher,

but, yes, true, and that's because of the high temperature that a steam boiler has to maintain to do its job. More loss when it's running that hot.

Tony Conner

Unless...

...there is a proper steam meter on the boiler (and the chances of that being the case are pretty much zero), and a stand alone gas or oil meter for the burner in that boiler (often not much more chance of that than the steam meter), you absolutely CAN NOT under any circumstances get a "boiler efficiency" number. What you've most likely been given is a "combustion efficiency" number. The confusion between these two values is something approaching total. They are very much NOT the same thing. Combustion eff is a component of boiler eff, and is the measure of how effectively the burner does it's job. The job the burner does is an important component of boiler eff, but the boiler itself is essentially just a heat exchanger, with the heat of combustion on one side, and the boiler water on the other. It's very possible to have a great burner, perfectly tuned, and still suffer poor boiler eff because the heat transfer surfaces in the boiler are scaled-up, or it's a crappy design. Boiler eff is a big picture-overall look at net heat out divided by heat in.

The poor old steam boiler often suffers unfairly from this confusion with efficiencies. Usually, the biggest single thing you can do to ensure the lowest fuel costs on a steam boiler is get all of the condensate back that you reasonably can. This means making sure that any condensate return pumps are working properly, and staying on top of any steam or condensate leaks. This does a couple of things. One is that the boiler gets a nice running start, making steam with 180*F condensate, instead of 40*F city water, and no make-up water means no scale to foul heat transfer surfaces. It also means no oxygen corrosion to kill your boiler long, before it's time.

It's also worth noting something about the water temps arriving at the boiler. The boiler will use a lot more fuel with a pound of 40* water showing up, rather than 180* condensate. If the boiler eff (NOT combustion eff) is 80%, then to add that missing 140* (140 BTU) to each pound of make up water, you'll have to burn about 175 more BTU of fuel. Bear in mind that this is PER POUND of water, over whatever the time period is. If it's over an entire heating season, this is a LOT of money. Getting the condensate back can save you that much fuel & money, right off the bat. Note that that if cold make up water is arriving at the boiler, even though the fuel costs jump to deliver the same amount of heat to your building, the BOILER EFF remains unchanged, since it looks at NET HEAT out. The fuel costs are far higher, but the boiler eff is unchanged. This situation indicates a SYSTEM problem, not a BOILER problem.

Boilerpro_3

There are condensing steamers available

that should give you efficiencies in the 90's, but as the wise one above said, burner efficiency is only part of boiler efficiency, and boiler efficiency is only part of system efficiency. Getting the sytem is top condition will give you the best efficiency out of any boiler.

Boilerpro

Jim Davis

65%-Something wrong

Having tested many old and new boilers, I have found that many old boilers can operate within a few percentage points of efficiency of new boilers when adjusted correctly. In fact I have found some old boilers that out perform any and all new boilers on the market. If the boiler is full of scale & sludge it needs to be cleaned. If the burner cannot be set for good operation, maybe just a new burner is necessary. I have had customers save $40,000 dollars a year with just a new burner.(might have been a bigger boiler than yours). If your contractor did a combustion analysis-Oxygen-Flue Temperature-Carbon Monoxide, do you have the numbers? Can interpret what they really mean!!

M Ransley

Every year we drain the boiler and run a hose in the clean outs at the bottom of the boiler and flush them clean.
I have never been told there is more to cleaning than that! It has scale im sure It hasnt been maintained right and I replaced some leaking , non closing radiator vents . So what do i do to remove scale and buildup.
I havnt had a burner test done yet.
Any you guys in Chicago

Jim Davis

Boiler Cleaning

Usually there is bake on scale that does not drain that might have to be chemically cleaned, but also could be electronically cleaned during the off season. I have students in Chicago that have been through my training that should know what to do. I do not have the list with me, it is at my office. I will not be there until Thursday-I will be in Lansing, MI, teaching. I will give you some names then.