Fresh Air Intake - InspectionNews

David Banks · #1 (**permalink**) 06-15-2007, 01:38 PM

Some one punched a hole in the hearth and installed this. Says fresh air intake. At first I thought they were using it as a clean out. Does not look like fire ever burned in the fireplace. Anyone seen before?

Bob Harper · #2 (**permalink**) 06-15-2007, 03:59 PM

Called the "Air-A-Lator" by Bernard Dalsin mfg. It carries a UL listing mark, though I don't see what std it is listed to in the catalogue.

There are variations on the Air-A lator such as sizes and one unit that is a box which sits over the ash dump yet places the air at the front of the fire. A separate screened intake is cut into the ash pit or the clean out door is replaced with an 8x8 screen made for that purpose.

HTH

David Banks · #3 (**permalink**) 06-15-2007, 04:40 PM

Bob why would they need fresh air intake? Any suggestions for comments or concerns with this set up? I would think most people would use as ash dump and hot ash would fall to basement floor next to furnace.

Jon Randolph · #4 (**permalink**) 06-15-2007, 06:52 PM

David,

Looks to me like that goes to the basement. Shouldn't fresh air should come from the exterior?

Is that wood burning? I would be worried about dropped coals.

Dale W. Feb · #5 (**permalink**) 06-15-2007, 09:06 PM

Looks like another "Ash Hole" sale pitch to me. Usually when a combustion air vent is added, it is because there is a negative pressure issue within the dwelling. This negative pressure competes with the natural draft fireplace. If this intake is connected directly to the basement, it will more than likely vent to the basement area and not up as intended. The basement is known to have the greatest negative pressures in the dwelling. Sometimes it is all about sales. I wonder what the cost of this addition was.

Jim Gecz · #6 (**permalink**) 06-16-2007, 01:11 AM

Quote:

Originally Posted by Dale W. Feb

If this intake is connected directly to the basement, it will more than likely vent to the basement area and not up as intended. The basement is known to have the greatest negative pressures in the dwelling. Sometimes it is all about sales.

So, then the exterior hearth has been compromised, correct? Air gets drawn down to the basement, stray ember along with it, and sets the pile of newspapers stored on the floor below.

David Banks · #7 (**permalink**) 06-16-2007, 02:58 AM

Thanks Dale. It does vent directly to the basement.Directly below and a few feet to the left is the gas furnace and gas water heater. It was poorly installed also.The whole unit was loose.

Bob Harper · #8 (**permalink**) 06-16-2007, 07:04 AM

combustion air intakes sounded like a good idea on paper so they were written into the codes in response to a widespread rise in smoking fireplaces. Afterall, if you have a tight house, then introducing outside air should cure the problem, right? Here is some basic info. to ponder:
The typical 36"x29" open hearth exhausts about 400-600 cfm, which includes combustion air( for the chemical oxidation of fuel) and excess air (goes along for the ride). You typical 4' air intake kit with one 90 degree ell and short run with no kinked hose at a 5 Pascal pressure gradient can flow about 12-15 cfm on a good day. On a bad day, when the inlet is under negative pressure, say as when on the leeward side of the home, it can actually backdraft. Dale has a video of one with flames shooting out with wind gusts! Now you know why the IRC required a metallic hose with a 1" clearance to combustibles on an air intake....

These air kits can be configured several ways. Some draw air from the ash pit, which may be totally sealed waiting on Geraldo to open it, have an iron door to the inside, and iron door to the outside, or one of these kits that replaces the outside door with a mesh/ louver device for admitting outdoor air. You'll see other brands on air kits that are nothing more than a 3" iron pipe with a very sloppy sliding door. These are either mortared in during construction or installed using a core drill. They introduct cold air right into the fire cooling and distorting the flames. One gas log mfr. I spoke with is thinking about recommending sealing these kits when their logs are installed because it blows out the pilot and causes sooting. At standby, they allow gobs of cold air to infiltrate.

Here is my recommendation on air kits: While the code requires their installation, the code cannot and does not require their use. Fix the house and the fireplace will work. Balance the house and it will draw sufficient warm air from the room without all these negatives. Better yet, replace the fireplace with a direct vent or power vented appliance such as a gas or pellet insert.

HTH

Dale W. Feb · #9 (**permalink**) 06-16-2007, 03:13 PM

Jim,

I might not use the term “compromised” as it appears that everything is non-combustible and no fire will result unless you open the vent door. I would state that the hearth extension has been modified to accommodate a combustion air vent. I would then recommend that they provide an “air-tight” metallic vent duct from the vent inlet, through the basement area (the reason for the air-tight requirement) and out to the exterior. If this is not possible, then recommend abandonment of the vent inlet (remove and close).

As a general note, the location of this inlet is perfect for the operation of a fireplace system. The air enters the fireplace with an equal balance. We are identifying many poor locations as attached to this post. The back wall and part of the side walls of a fireplace are under positive pressure as the air moves into the firebox. The attached photos show the intake located at the rear wall of the firebox. The round aluminum air duct enters into the square metal slider sleeve without a transition or seal. There were three masonry fireplaces with “Class A” chimneys at this 30 million dollar residence. All three vents (outside of the firebox) where enclosed within a wood framed chase. I could see the framing and wall insulation on all three. We were very fortunate because of limited use. The outside combustion air vents are not normally considered a potential fire hazard. But as Bob and I have mentioned, they can be a real threat. These systems must be properly inspected to ensure our clients safety.

The photos depict the location of the air inlets and a view through the inspection mirror down to the aluminum air duct. The last photo shows the wood framed chase that surrounds the masonry fireplace, Class A chimney and aluminum air duct. The other two fireplaces were constructed on the interior of the dwelling.

Bob Harper · #10 (**permalink**) 06-16-2007, 07:42 PM

Another thing of interest is all the lint clogging the screen thereby effectively reducing the flow capacity severely while placing combustibles (lint) in the duct. Just add heat because you have the fuel and oxygen. If this duct sees higher temps from adverse pressure effects such as flow reversals, the lint begins to pyrolize and thus have a lower ignition temp.

Dale, you shouldn't be showing off your own house.

While Dale has these pics up, can anybody draw any conclusions on how these people burn fires based on the pics presented?

Nick Ostrowski · #11 (**permalink**) 06-16-2007, 07:53 PM

Bob, the main thing I see is that the lower section of the firebox is pretty clean and all the sooting is taking place in the upper sections. But I don't know what this signifys.

Bob Harper · #12 (**permalink**) 06-16-2007, 08:06 PM

What kind of soot pattern on the rear refractory would you expect from a hot fire versus a smoldering sooty fire?

Part B, what effect does the grate have on this?

Dale W. Feb · #13 (**permalink**) 06-16-2007, 09:08 PM

Will this help?
This is what happens when you spend so much money on a house. You can't afford food or fire wood. It is interesting how both are fuels.