Should I Put a Louvered Vent in My Furnace Room Door?

Hi all,

The other day as I was loading my fire I had a situation where smoke from the coal furnace started to back into the furnace room after I closed the loading door. At the time I had my "smoke catcher" (pic1) turned on, as well as the vent for my oil furnace was on since the oil furnace just shut off so the vent was still on. It usually stays on for several minutes after the oil furnace shuts off. The smoke started to come from around the loading door and a few other places until I shut my "smoke catcher" off and oil furnace emergency switch. What I noticed is that smoke was also drawn to the baro damper on my oil furnace.

So somebody mentioned that I should have a louvered vent on the door to my furnace room and this may eliminate or at least reduce the possibility of this happening again. The door to my furnace room is always closed and when the coal furnace is on, you can feel air passing under the door into the furnace room quite swiftly. Does anybody have any thoughts on this? Should I put a vent in the door?

Jason.

Combustion air is critical. the rule of thumb is for every 2000 BTU's there's one square inch of
fresh air is required. for a 100,000 BTU furnace, gas fired or oil fired, than a 50 square inch fresh
air vent is required. note if a louver is used than this will decrease the size of the opening.
therefore the above would reqiure 100 sq inches. Combustion air can be drawn from adjoining spaces
but not reccomended. your currently system is the under cut door method. this is typical for
return air systems for cooling.

You are creating alot of negative pressure in that room between your boiler exhaust, your smoke catcher and the oil vent. Nature doesn't like a vacuum. That make up air has to come from somewhere. I'd say better to bring in outside air to the room.

I think coalkirk is right.
You probably have a negative pressure situation with so many vents pulling air out of that room.

Can the coal boiler handle the heat demand by itself?
It would help just to run one boiler and cap the other flue off.

Be sure you have working CO monitors.

Jason
You have a power venter that pulls big air from your furnace room. Leave the door open. You can put in return air grills
12 inch off the floor and 12 inch from the ceiling. Size would be calculated like Maurizziot had in his post. I could check the code book if you'd like.

Don't pull a vacuum on your whole house !! Put in an outside air source.. A 4" minimum duct, either dryer vent or PVC pipe from outside the house into the furnace room..
This outside air vent will supply the room with fresh air and this will reduce or eliminate the vacuum on the rest of the house..

I see no reason to pull heated air from the rest of your house and burn it in your furnaces. Use fresh outside air and eliminate the vacuum on the rest of the house... The vacuum is pulling cold air through cracks around doors and windows.. and pulling this cold outside air into the heated living spaces.. making cold drafty rooms.
Providing an outside air source for your furnace room make the whole house warmer by eliminating the drafts..

Do a search for 'outside air' on this forum.. there are several good threads on the subject.

Greg L

WOW....thank you all for the great information. I think what I'm going to try is bring in fresh air from outside, as some of you suggested. My plan is to run a dryer vent through the wall into my coal bin and then out through the Plywood that is covering the window into my coal bin. This is the simplist solution for me and I won't have make another hole in my foundation.

Sounds like a good plan,, put a piece of mesh or screen over the outside opening to keep leaves and critters out of the house..

I'll bet that you will immediately find that the rush of air under the door to the furnace room is gone.. and a few of those drafts around windows and doors go away too..

Let us know how it works out.

Greg L.

I've read about the "one sq inch per 2,000 BTU's" and when I did the math I thought "That's a big hole!". Then someplace else I read something like " Every building leaks some, figure one sq inch after 80,000 BTU's" so if you have a 100,000 BTU unit, figure the one sq" on 20,000....for ten sq inches. A 4" dryer vent is 12.5 sq inches. That makes sense and is an easy place to start. I've personally seen a few oil boilers that didn't get enough make up air. Every one was cured with a 4" vent.

Chapter 17 IRC looks at combustion air from inside and outside.
In a nut shell; air from inside you take total input btu/h of all appliances within the space and then 1 sq inch per 1,000 btu/h
that gives you the FREE AIR size of each opening located 1 within 12 in of flr, the other within 12 in of ceiling.
So 100k boiler and 120k coal boiler would need 220 sq in per opening
Outside air sizing and location is the same, just in a horizontal duct run 2,000 btu/h is used and in verticial 4,000 btu/h is used
So horizontal would require 110 sq in each and vert would require 55 sq in each

Bringing outside air in is the way to go, keep the 90* bends to a minimum. I have a total run of 23' of 4" duct with 2-90* and 1- 45* bend and have been told by my burner tech. that any more bends and i'd have to go up to 5' duct.

JB