Combustion Air

Paul_28

I like to know the best method to bring combustion air into a 10’ X 6’ boiler room that has one outside wall. Ideas???

Big Ed

You need 1 square inch of "opening" per 1000 btu "input" of the combined units..... Two vents upper and lower , outside wall

Crorrection per 1000 btu , thanks for spotting typo Marc

Firedragon_4

Make sure that's

'free-air' space too! Those grills have frames and the vanes take up room too! Have a pro size it from an OEM chart.

marc

1 square inch per 1000 btu not 1 btu

Unknown

Combustion Air

When bringing in outside air to the room it is 1 square inch per 4,000 btu's. One grill high and one low and as George stated, that needs to be free area of the grill. The 1 square inch per 1,000 btu rule is when you are using air from an interior space. Another method would involve installing a Field "Fan in the Can" or a Tjernlund "Inforcer" motorized combustion air device. Hope this helps.

Glenn Stanton

Manager of Training

Burnham Hydronics

www.burnham.com

tim smith

combustion air

Also this formula changes if you need to duct horizontally to the space, it then goes to 1 sq. inch per 2000 btus for the horizontal ducts.

Maine doug_2

Usually

a hole in the wall is the best way. If you do not want cold air running in when the boiler is off, a damper controlled by the boiler should do it. A screen on the outside to keep critters out.

enough to be dangerous

sealed combustion

is there is anything wrong with bringing in the
outside air in a duct that is brought
directly to the boiler intake air area.
If attached nicely would this not be a
"sealed combustion" boiler.
Asumming the duct and intake area are sufficient is there
any problem with doing this?
This would keep all the cold air out of the building.

Constantin

In fact,

...a number of burners/boilers allow this sort of installation, even on the oil side. The Beckett NX Burner has a special housing that allows you to hook up a pipe from the great outdoors for direct vent operation, which is one way of implementing sealed combustion.

Viessmann offers no such luck with the Vitoflame 100. Allegedly, condensing moisture and whatnot are concerns.

BTW, sealed combustion doesn't just isolate cold air from the building envelope, it also prevents combustion byproducts from spilling into the home. This is the most attractive feature to me.

Constantin

Alternatively,

you could consider the TamTech Cape Backdraft Damper. It's a 4" or a 6" Dia. tube with a cloth-based one-way valve that opens and closes automagically. Allegedly, it has a neglible impact on restricting airflow and hence should be ideal for our boiler room and dryer exhaust.

Firedragon_4

Just make sure

it's at least 12 feet long and try to warm it up. Cold air creates cold combustion air and if you look at most burners it comes in around the pump and that creates cold oil, get it???

Outside air should only be a last resort, FACT!

Gordy

Question

If we induce outside combustion air say -15* would this not pose a worse condensation scenerio with in a CI atmospheric boiler? Versus using ambient air from the dwelling.

I would like to do this also but this was a concern for me. I guess it would be mixing with ambient air somewhat,depending on the setup since it would not be sealed combustion in the true form.
Gordy

Constantin

Not sure why you'd think this...

... the outside air comes in at -15°F, true. However, before it touches the HX on the inside of the boiler, it's been through a flame that's over a thousand degrees hot.

Could the air condense elsewhere before it hits the rotor and the flame? Possibly. But consider how likely it is for the exterior air to be warmer than the inside appliances during the heating season and hence be capable of condensing on them. Winter air is very dry...

Gordy

Costantin

I'm only asking the question. Not implieing that would be the case.Just a thought I had. Thanks for the info.:)

Constantin

Sorry, I didn't mean to be curt!

Hey, I'm just a silly homeowner, not a heating professional, so take my musings with a grain of salt. Must be that engineering degree getting in the way again.

But seriously, I doubt you would have trouble with a burner that has been engineered for DV use like the Beckett NX. Otherwise, Beckett wouldn't have a specific shroud that accepts exterior air, right?

Lastly, looking at my Vitoflame 100, I notice that the combustion air opening is to the left side...a tiny slot of about 1"x3". If I ran a combustion air nozzle to that thing (stepping down from the 4" Viessmann calls for), there would be no need to come even close to the motor, oil, etc. with that combustion air.

I'd think that the only thing that would get colder is the mixing chamber, the blower, etc. The flame temperature might suffer a bit as well, but if you use single-wall Al pipe to bring the outside air in, it would get warmed a great deal before it got to the boiler, all while keeping the combustion products out of your home. Also, there is the barometric damper that also requires an air supply.

Gordy

I took it as being direct not curt,I like that. Well I have a gas fired Weil McClain. My only thought on this was I have four fireplaces and if I light Two I trip the spill switch on the draft hood if the boiler decides to cycle not good I know. So I went to opening the basement window a crack when burning which solved the problem.Guess I tightened up the house a little more than it liked. there fore I would like to do something a little more automatic. Sounds like your boiler is made to do the modification.

Gordy

Weezbo

Ok....

this is not quite in this thread however i wish to ask,have any of you ever installed a gas fired condensing boiler with the proper sized "holes" in the room on a foot off the floor and the other a foot down from the finished ceiling and found you Were Not getting sufficent air in a boiler room? i havent however someone told me something a few years back and its got me wondering...

Gordy

Wondering what?

Joe_30

[1] In winter with north wind howling what keeps the Cape damper, or any non-gear driven outside air damper, from standing wide open due to strong outside pressure on the side of the house.?

[2] Wouldn't a really good outside air supply damper be wired to the clothes dryer as well [assuming its near the boier] , and designed to open even wider when both boiler and dryer are on?

Constantin

Interesting Points...

... The backdraft damper is supposed to work like a Trapguard (which prevents water/gas from floors drains entering the house). That is, it opens easily one-way and prevents all air movement from the other way. Whether it works or not is up to debate. Only time will tell (that is, unless someone here has experience with one).

Naturally, a backdraft damper won't do you much good if the house is under positive pressure. Under such circumstances, it'll simply let all the excess pressure out. So I agree with you that a motorized damper would probably perform better. However, it is a more complicated solution, more expensive, and more likely to fail one way or the other than a simple cloth-based check valve.

I inquired about sealed combustion with gas dryers. Apparently, it is not possible. Thus, the best you can do is to turn the laundry room into an airtight space that isolates it from the rest of the house. However, I didn't want to be that extreme. The HRV/ERV inlet and outlet in that room should allow the dryer to fire w/o issues. We'll install a outdoor door to keep things tight and quiet, but that's as far as I'll go.

Under ideal conditions you'd have a motorized inlet/outlet damper that would operate reliably in a lint-rich environment. However, I doubt that any affordable, motorized dampers would be happy to deal with all that lint. Furthermore, wiring it all up is again complicated and prone to failure over time.

Lastly, the boiler and the dryer are in separate locations. Wiring the logic into a boiler is much simpler, since many of them are built with such dampers in mind. However, the simplicity of the check-valve + a U-trap is mighty appealing. Hence, I will try that first.

Bob Morrison_3

Two methods described in NFPA 54 (5.3) for NG

What fuel are you utilizing? If natural gas, then one of two methods will apply for a "confined space". Check you local code. In MA. the second method does not meet code.

The first and traditional method has been described in some of the other posts: all air from outdoors, two permanent openings, one 12" from the floor, the other 12" from the ceiling; vertical openings (or ducts) sized at 1 sq. in. per 4000 BTUh input; if horizontal ducts then 1 sq. in. per 2000 BTUh.

Method 2 is the updated approach and requires on one permanent opening within 12" of the ceiling at 3000 BTUh per sq. in. given appliance clearance requirements are met.

For the boiler in my very tight house (73 MBH input) I installed a 6" round duct terminated to an outside wall louver. I do not have a motorized damper, not do I believe that I need one to avoid excess infiltration for my room. if air can't exit, then it can't enter: a tight room with one opening will not infiltrate. If you don't believe me, try blowing into a soda bottle. The interior duct drops in from of the boiler away from piping - the outdoor air should be able to mix with room air before contacting any pipes.

Bob

enough to be dangerous

well then.......

if I had an air intake duct and with suitable
skill (not that I have it) construct a beautiful sheet metal shroud around the bottom of my water heater will the water heater continue to work properly. It is not a fan forced type. It just goes up the chimney.

pasquale