Outside Combustion Air?

titleist1 · Post by **titleist1** » Sun. Oct. 23, 2016 3:13 pm

Larry, how big is the combustion fan intake opening on your stoker?

lsayre · Post by **lsayre** » Sun. Oct. 23, 2016 4:08 pm

titleist1 wrote:Larry, how big is the combustion fan intake opening on your stoker?

The AHS Coal Gun is not a conventional stoker, so I have no idea if this has a proper answer. It is more akin to a fan assisted hopper equipped hand fed boiler that ashes mechanically, and thereby stokes. Technically there is no port for fan intake air, and the fan does not serve as a blower. The combustion air comes from whatever air the chimney can suck up through the ashes after the fan pulls the "over the fire air" flapper cover closed tight. Other than pulling the over the fire air flapper shut the fan (as far as I can tell) merely swirls the hot air from the firetube rapidly around the "swirl chamber" so maximal heat transfer into the water that surrounds it can occur before the chimney draws it out. A work of genius by the engineer/professors at Penn State University, as in the process of swirling the air, a low pressure region is created in the center of the swirl chamber, and this low pressure is what sucks the over the fire air 'flapper' cover closed tight.

lsayre · Post by **lsayre** » Sun. Oct. 23, 2016 7:50 pm

lsayre wrote:I found this on the internet:
Total Sq .In. of Combustion Air Intake Opening = Total Input BTUH / 1000
If my boiler has 130,000 input BTUH then: 130,000/1000 = 130 Sq In.
130/Pi = 41.38
Sqrt (41.38) = 6.43
6.43 x 2 = 12.86" ID (for round pipe)
That's a huge pipe ID to meet outside air requirements per the code.

If I'm reading the code correctly, this outside air must be split into two completely separate duct pipes, one terminating within 12" of the ceiling, and one terminating within 12" of the floor.

It looks like to 'almost' fully meet code with regard to outside supply air for my specific boiler would require (at minimum) 2 x 9" ID round pipes (ducts), with one terminating near the ceiling, and one terminating near the floor. The two would provide 127 Sq-In. of intake when combined.

And if the case can be made that the maximum real input of my S130 boiler is only 116,000 BTUH, then 2 x 8" ID pipes (ducts) would suffice. This degree of outside air supply would permit me to completely close off my boiler room from the basement.

McGiever · Post by **McGiever** » Sun. Oct. 23, 2016 8:34 pm

titleist1 wrote:Larry, how big is the combustion fan intake opening on your stoker?

Never measured a Coal Gun like Larry's, but my very similar Axeman breaths through an 11" dia. fire tube stuffed full of pea coal.
And it does use a 1/4 hp motor turning at 1725 rpm with 13" fan vanes.
BTW: This fan is very hot sitting at the half way point of the double pass inferno stream of hot gases running out and back again.

titleist1 · Post by **titleist1** » Sun. Oct. 23, 2016 9:16 pm

lsayre wrote: If I'm reading the code correctly, this outside air must be split into two completely separate duct pipes, one terminating within 12" of the ceiling, and one terminating within 12" of the floor.

When we redid the furnace room (propane) at the church that is how the supply air openings had to be cut, one at the ceiling and one closer to the floor. It wasn't 'outside air' since these openings were into the adjoining room. That is what the code required at that time, maybe 15 years ago. We also knocked out one of the outside wall blocks and put a vent there so it was taking in some outside air too, but that was not required. Interestingly one of the PT places around here built about 8 years ago has a propane water heater, an 80 gallon unit, and the laundry room where it is located had to have a vent to the outside like we put in the church. But there are no separate wall openings as an air supply, probably because the combustion air is minimal compared to a furnace.

titleist1 · Post by **titleist1** » Sun. Oct. 23, 2016 9:33 pm

lsayre wrote:I found this on the internet:

Total Sq .In. of Combustion Air Intake Opening = Total Input BTUH / 1000

If my boiler has 130,000 input BTUH then: 130,000/1000 = 130 Sq In.

130/Pi = 41.38

Sqrt (41.38) = 6.43

6.43 x 2 = 12.86" ID (for round pipe)

That's a huge pipe ID to meet outside air requirements per the code.

I'm not sure what type combustion appliance that formula is to be used for, but the numbers don't work for our propane furnace. Ours, a bryant 350MAV036080 is rated at 80,000 btu's, which using that formula would indicate roughly a 5" pipe. But the outside air pipe feeding the combustion fan at the unit starts as a 3" pipe and is necked down to a 2" pipe at the unit. The exhaust is the same 2" pipe at the unit and a 3" pipe out the wall. Maybe the high efficiency units use a different formula.

Scottscoaled · Post by **Scottscoaled** » Sun. Oct. 23, 2016 10:02 pm

Pulse fired.

swyman · Post by **swyman** » Sun. Oct. 23, 2016 11:26 pm

Scottscoaled wrote: It would be an interesting follow up to see if it allows you to keep your house warmer with less coal. That topic hasn't been really explored here as it should have.

You know that is the whole reason for me in doing the addition? I could just not come up with a good place to put it in my basement especially since it is only about 6' 5" deep. I was a little beside myself at how much coal I was burning last year BUT my expectations were based off of what other people were burning. I did not take into consideration how much area I was heating, once I looked at the big picture I changed my tune but boy was it a struggle for my hard headedness to grasp. I pissed off a few people on here last season due to being hard headed and upset with what I thought was bad performance, but I think we are all good. I am glad they accepted my apologies and stuck with me.....lord knows I needed the help, was really close to calling it quits a few times. I am very excited to say the least to get this installed in the new basement when it gets finished and I hope this will help others! I due expect my coal consumption to go down some, just not sure how much. If anything I hope the boiler will be able to solely heat my house on the coldest days without help from the furnace. Having a 200' shorter run and larger diameter pipe should do the trick?

swyman · Post by **swyman** » Sun. Oct. 23, 2016 11:34 pm

titleist1 wrote:
Since you are in the process of construction, I would pipe for outside combustion air now. It may not make a big difference now but as you start sealing up the rest of the house I think you will see the benefit.

Excellent post titleist, I didn't think anything about insulating the existing walls. My builder says they will put some type of coating on the outside walls of the new construction, then add insulation boards and backfill 1st 2' with #6 stone and the rest of the way with sand. I won't get to insulating the existing walls this season but now you can bet I will be checking the temperature differences between the old and the new walls.

swyman · Post by **swyman** » Sun. Oct. 23, 2016 11:46 pm

lsayre wrote:
lsayre wrote:I found this on the internet:
Total Sq .In. of Combustion Air Intake Opening = Total Input BTUH / 1000
If my boiler has 130,000 input BTUH then: 130,000/1000 = 130 Sq In.
130/Pi = 41.38
Sqrt (41.38) = 6.43
6.43 x 2 = 12.86" ID (for round pipe)
That's a huge pipe ID to meet outside air requirements per the code.
If I'm reading the code correctly, this outside air must be split into two completely separate duct pipes, one terminating within 12" of the ceiling, and one terminating within 12" of the floor.

It looks like to 'almost' fully meet code with regard to outside supply air for my specific boiler would require (at minimum) 2 x 9" ID round pipes (ducts), with one terminating near the ceiling, and one terminating near the floor. The two would provide 127 Sq-In. of intake when combined.

And if the case can be made that the maximum real input of my S130 boiler is only 116,000 BTUH, then 2 x 8" ID pipes (ducts) would suffice. This degree of outside air supply would permit me to completely close off my boiler room from the basement.

Wow these numbers are scaring me! I though I could just run a piece of 4" pvc and connect it to both fan inlets?

Scottscoaled · Post by **Scottscoaled** » Sun. Oct. 23, 2016 11:55 pm

I take it that your addition doesn't actually draw air from the old part of the house? That's good. Your boiler won't be the cause of a bunch of cold drafts. So just run 2- 4" pvc's.

swyman · Post by **swyman** » Mon. Oct. 24, 2016 1:51 am

Scottscoaled wrote:I take it that your addition doesn't actually draw air from the old part of the house? That's good. Your boiler won't be the cause of a bunch of cold drafts. So just run 2- 4" pvc's.

The new part is going to be connected. Once they get the shell built we are going to cut a 4' wide opening connecting the new basement. I know I have some drafts, I just thought if I brought in outside air and connected straight to the blowers that is would lessen the leakage if that makes sense? Maybe there is too many leaks in my house to worry about it but it seems to me it would have to help?

hotblast1357 · Post by **hotblast1357** » Mon. Oct. 24, 2016 5:31 am

Put a window in the basement wall while you are at it, then AFTER the boiler is all installed and running, if we figure out you need outside combustion air, you can open the window a little, I do not believe it HAS to connect to the combustion fans, that just sounds like trouble....

lsayre · Post by **lsayre** » Mon. Oct. 24, 2016 5:33 am

Here is what I believe to be the New Jersey residential solid fuel appliance requirement for outside supply air openings:

M1703.1 Outdoor air. Where the space in which fuel-burning appliances are located does not meet the criterion for indoor air specified in Section M1702, outside combustion air shall be supplied as specified in Section M1703.2.

M1703.2 Two openings or ducts. Outside combustion air shall be supplied through openings or ducts, as illustrated in Figures M1703.2(1), M1703.2(2), 1703.2(3) and M1703.2(4). One opening shall be within 12 inches (305 mm) of the top of the enclosure, and one within 12 inches (305 mm) of the bottom of the enclosure. openings are permitted to connect to spaces directly communicating with the outdoors, such as ventilated crawl spaces or ventilated attic spaces. The same duct or opening shall not serve both combustion air openings. The duct serving the upper opening shall be level or extend upward from the appliance space.

M1703.2.1 Size of openings. Where directly communicating with the outdoors, or where communicating with the outdoors by means of vertical ducts, each opening shall have a free area of at least 1 square inch per 4,000 Btu/per hour (550 mm 2 /kW) of total input rating of all appliances in the space. Where horizontal ducts are used, each opening shall have a free area of at least 1 square inch per 2,000 Btu/per hour (1100 mm 2 /kW) of total input of all appliances in the space. Ducts shall be of the same minimum cross-sectional area as the required free area of the openings to which they connect. The minimum cross-sectional dimension of rectangular air ducts shall be 3 inches (76 mm).

http://www2.iccsafe.org/states/newjersey/nj_residential/PDFs/NJ_Res_Chapter17.pdf

I'm not sure if this differs from National code, or from other State or local codes. I speculate that the code as written may contain a level of what may prove to be "double redundancy" by which to provide a significant margin to the safe side.

McGiever · Post by **McGiever** » Mon. Oct. 24, 2016 11:26 am

I must point out that the 3" minimum cross sectional dimension referenced above is but one dimension of a rectangle. So...even before one begins to do any of the needed math you would be starting out with a 3" min. dimension on the one side of the rectangle multiplied times(x) an unknown yet to be calculated dimension of the opposite side of the rectangle.

I was skerd that some would be too quick to see it as 3" min. diameter for a pipe and end up vastly undersized from the intended size.

INTERNATIONAL RESIDENTIAL CODE 2006, NEW JERSEY EDITION
325
COMBUSTION AIR
For SI: 1 square inch = 645.16 mm
2
, 1 British thermal unit per hour = 0.2931 W.
NOTE: Each opening shall have a free area of not less than 1 square inch per 4,000 Btu/h of the total input rating of all appliances in the enclosure.
FIGURE M1703.2(1)
APPLIANCES LOCATED IN CONFINED SPACES—ALL AIR TAKEN
FROM OUTDOORS THROUGH TWO OPENINGS

For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm
2
, 1 British thermal unit per hour = 0.2931 W.
NOTE: Each opening shall have a free area of at least 1 square inch per 2,000 Btu/h of the total input of all appliances in the
space.
FIGURE M1703.2(2)
APPLIANCES LOCATED IN CONFINED SPACES—ALL AIR TAKEN
FROM OUTDOORS THROUGH HORIZONTAL DUCTS

For SI: 1 inch = 25.4 mm, 1 British thermal unit per hour = 0.2931 W, 1 square inch = 645.16 mm
2
.
NOTE: Each opening shall have a free area of at least 1 square inch per 4,000 Btu/h of the total input of all appliances in the space. The attic must be sufficiently vented
for combustion air to be taken from the attic.
FIGURE M1703.2(3)
APPLIANCES LOCATED IN CONFINED SPACES—ALL AIR TAKEN FROM OUTDOORS THROUGH VENTILATED ATTIC

For SI: 1 square inch = 645.16 mm
2
, 1 British thermal unit per hour = 0.2931 W.
NOTE: The inlet and outlet air openings shall have a free area of not less than 1 square inch per 4,000 Btu/h of the total input rating of all appliances in t
he enclosure.
FIGURE M1703.2(4)
APPLIANCES LOCATED IN CONFINED SPACES—INLET AIR TAKEN FROM
VENTILATED CRAWL SPACE AND OUTLET AIR TO VENTILATED ATTIC

For SI: 1 inch = 25.4 mm, 1 British thermal unit per hour = 0.2931 W, 1 square inch = 645.16 mm
2
.
NOTE: Each duct shall have a free area of at least 1 square inch per 4,000 Btu/h of the total input of all appliances in the space. The attic must be sufficiently ventilated
to provide the required combustion air.
FIGURE M1703.3
APPLIANCES LOCATED IN CONFINED SPACES—ALL AIR TAKEN
FROM OUTDOORS THROUGH VENTILATED ATTIC, INLET DUCT WITHIN OUTLET DUCT