Replacement air for combustion?

RoiiRaz

Hi all,



Another question: My boiler room is fully open to outside air. There's a heavy grate vent in place of what would have been a basement window in the boiler room. In the boiler room, I have a 75 gallon gas-fired water heater and my 400k BTU steam boiler, with its condensate collector (not insulated). Does this much ventilation sound reasonable? I don't often see rooms which are completely open to outside air.



thanks again.

Hap_Hazzard

Br-r-r-r-r!

I get cold just thinking about leaving a basement window open, but really it depends on how the house is constructed.



In my house the basement door has louvers and there are several vent holes cut in the first floor, so the boiler draws air from the living space. Of course, that means air has to leak in to replace it.



When you think about it, this is really stupid. It makes the house feel drafty and it sucks all the moisture out of the house, and my nose starts bleeding around the middle of December and doesn't stop until May. Adding a vent damper has helped a lot--at least the indoor air is only being drawn up the flue when the burners are running--but it's still a waste of warm indoor air.



But then, leaving a basement window open would be just about as bad. It would get better if I replaced the basement door and covered the vents in the floor. But it would still get cold down in the basement. A smaller opening would be less prone to drafts but would still allow ample air for combustion.



I'm not sure what the ratio is, but the air going up the chimney is expanded considerably compared to the cold, outside air, so, in theory, the intake doesn't need to be as big as the flue. Maybe something the size of a dryer vent, with the flap on the inside?



I'm just guessing, and that's why I haven't actually tried it yet, because if you get it wrong, the consequences would be horrific. If you can't draw in enough air to move the exhaust gases up the flue, they overspill the draft hood and escape into the living space, seep through the floorboards and kill people. I might install everything, test the draft and spillover and find everything working fine and then days later a drop in barometric pressure or a cold front could throw off the balance enough to make it stop drawing. We've all seen the effect the weather can have on a fireplace.



I think this is why old-timers tended to err on the side of allowing excess air in.

SWEI

Don't guess

there are codes for this, and clear numbers for square inches of effective free area.  They still misbehave at least some of the time, which is why more and more boilers operate using sealed combustion.

BobC

I just installed

a 4" dryer vent (flap removed) in a basement window pane and ran some 4" duct over to my shrouded EZ-Gas burner to cut down the draft I used to feel when she fired. It cut the draft by about 75%. My boiler is A LOT smaller than the one your talking about.



I have a friend that did his basement over years ago and ended up with an enclosed boiler room that was about 8 ft sq in the corner of the house which was very heavily sealed and insulated. He had a small single hung window in that corner, I told him to open it 1/2", and pin it so the gas fired boiler and HWH could breath. No drafts in that house at all.



Bob

Hap_Hazzard

I will probably end up with a power burner

long before I ever attempt anything like I was describing. This old boiler won't last forever, and those setups Steamhead installs are making me salivate.

RoiiRaz

Sealed burner boilers...?

Do they exist for new steam boilers?

gerry gill

Fan in a can

is a nice unit for smaller boilers, and the bigger ones we started using powered dampers in the walls with ignition interlocks that we get from Grainger.

bx1000

Been there

I've got a very similar arrangement, metal louvers where a window once was. When we replaced the boiler recently I wanted to close this up, but the installer (a Steamhead, not a knucklehead) insisted on keeping it. What we did instead was insulate the interior walls of the boiler room, and ultimately we ended up making the boiler room door into an exterior type door (added door sweep and weatherstripping) to keep the draft out.



It's been a mixed blessing. No drafts in the rest of the house, and it works fine when the boiler is running. But if the boiler stops...



The steam pipes are all insulated, but some nearby water lines (including a small copper line supplying the boiler water meter/feeder) are not. Of course, during the first blast of Arctic weather we got this winter, the boiler went out overnight (due to a flakey transformer). The house held temperature pretty well overnight and it was an easy fix in the morning. When the boiler came back on in the morning I was massively relieved, as I had been worried about the risk of pipe freeze all night. Just as the boiler started to make steam and I started to relax, the water feeder line gave out, spraying right onto the header, filling my entire basement with a cloud of steam/vapor.



I'm seriously thinking about the boiler interlocked fans now.

SWEI

One option

From UMC 701.11 (derived from NFPA 54):



With prior approval, power-actuated movable louvers admitting combustion air may be used and, if installed, shall be electrically interlocked with the main burner fuel-supply valve so as to prevent fuel delivery unless the louvers are in the fully open position.

RoiiRaz

Thanks!

will look at some of these.

Joe V_2

perform due diligemce but

I believe it is one sq in per 1000 btu input with a minimum of 12 sq inches opening to outside