open damper v efficiency

Brad White_15

1) If you see the ratings of a boiler with a vent damper and without, there is one difference (usually lumped in with electronic ignition, ie: "EI and Vent Damper"). Given that manufacturers have offered these options for 25 years, it is by memory that I am stating that the difference is between five and eight AFUE points for the damper on an atmospherically fired boiler. For having a standing pilot (not having the electronic ignition portion) I figure those at about 50 therms a year but this can vary up or down 50 percent or more. So if you lose eight percent and that is all it is, what is that dollar amount on your fuel bill? And that is not really a good number because those effiencies are laboratory-based, not real-world.

The DOE ratings are measured in a laboratory under ideal conditions for boilers that have run for 20 minutes. Your boiler is over-sized so I would double the loss (or double the benefit) as a SWAG...

2) I would consider if the boiler was in your basement (normally would be for that one) and if the air it draws is from your prime heated space or from the basement. I assume the basement. But the draft has to come from somewhere so I would think that half would be from your heated space, boiler running or not. If the flue is say, 6-inch, the draw could be as much as 150 cfm (rough guess not corrected for firing temperatures). If half of this comes from the house and you do not care about a cold basement, it might cost you 5,000 BTU's an hour on a design day depending on your climate of course. Windy? A lot more. Some through the boiler firing chamber the rest through the draft diverter.

Bottom line here is this affects more than your boiler room heat loss. It draws from the house at some level too. Has to.

3) Given that your boiler is over-sized by your posting, consider that each cycle has to warm up and then lose all of that heated mass to the atmosphere. And because it is over-sized, those cycles occur with annoying frequency, I bet. Every time, your 18 wheeler accellerates up the hill and coasts down losing all momentum until it settles in a valley to start again....

Final Point: No matter how you slice it, analyze it or examine the variables: Replace the damper. Do not leave it like that for longer than you have to :)

dtc

open damper v efficiency

Since moving to new house this winter, been having problem of spill switch randomly opening due to residual heat of oversized WM EG55 boiler AFTER boiler shut off and damper closed. New switch didn't fix problem.

After reading on this site, I tested different components one by one. While jumpering safety wires temporarily, used meter on spill switch itself to finally pinpoint problem.

Since I don't want to and wouldn't bypass the spill switch, I "solved" the problem by locking the damper open. This may actually be good for the chimney in preventing condensation, but am I losing much efficiency??

Is this a tremendous loss of efficiency, or just a little, could anyone give me a very rough estimate of how much this is costing me each month? Thanks in advance.

Dale

knock out

Alot of dampers have a 1" knock out plug for use with standing pilots, you could try removing it if it has one. Also, you could confirm the input of the boiler and see if it could be lessened. And,the placement of the vent damper may be moved up in most cases as long as it's below the dillution air opening.

Boilerpro_3

If this a steamer

I have seen this problem when the boiler water was very dirty and surging and even with an open pilot vent hole. The boilers needs a very good cleaning,in this case.

Boilerpro

dtc

Good info, thanks.