Chimney venting

Should a Gas furnace and water heater that vent to a masonry chimney be B-vents? I did an inspection that has single wall venting into the chimney. I can not determine if a chimney liner is present because I can not access the it from the roof or the access door (stuck closed). Which brings another question. Why would it have an access or clean out door when there is not a fireplace present? Maybe it used to have a fireplace? Anyway, my main question is about the venting.

I am concerned because the chimney exterior has efflorescence, I think either the liner is disconnected, does not extend all the way up the chimney, or the vent is not sealed properly.


There are a few variables to determine if a liner and cap are needed.

Age of mechanical systems. Also type of mechanical systems (Efficiency)

Chimney on exterior vs, interior. Exterior chimney has 3 sides exposed to elements.

Local jurisdiction.

Do you have a picture of the chimney crown/flue. (Top portion)

It is required to have a clean out on a mechanical chimney. This is to remove a possible build up of debris. The INachi advanced heating course address why a chimney clean out is needed.

I would say this chimney has no liner and cap. This is an exterior chimney that should have a liner installed as there is efflorescence present.

I see around here all the time that people use the wrong caps for the application. Like spark arrestors for newer mid efficiency furnaces or they have a new high efficiency furnace installed but leave the water venting up the chimney with no cap or the wrong type.

What David said, plus:

Single wall is fine, in a basement, provided it has 6" clearance to combustibles.

The cap needs to be replaced because it is a screen with no cover. Mid efficiency gas furnace about 6 years old. I agree the liner is the issue. I will probably recommend having a chimney sweep scope the chimney. The chimney is too high for me to look down.

I see those screens all the time. They are for the birds!! In Ohio there is a code that requires liners and caps. But it depends on the age and type of systems.

I think you are giving your client good advice to have a liner and cap installed.They are only 300-500 hundred. Good job Mike!!

I had a tough call on a house yesterday in regards to the chimneys.
There were 2 stacks. One in the middle of the house and one on the front exterior. The middle chimney had one flue, the outside chimney has 2 flues. House had 2 fireplaces, boiler, incinerator and water heater.

Nothing was venting up the middle chimney:shock:

The incinerator was disconnected.

The basement fireplace was vented out the side of the house. It was stuffed with pillows and was in need of a sledge hammer.

The first floor fireplace appeared to vent up one exterior chimney flue. The water heater and boiler seemed to go up the other.

On the exterior was just screens, No cleanouts in basement. Age of boiler 13 years and water heater was 4. I could not verify if fireplace and mechanicals were separated. The exterior chimney brick/mortar looked good. I still advised having proper caps installed and to have flues reviewed for proper applications. Fireplace was full of soot and ashes.

Just thought I would share. This house was weird. 1300 sq.ft. 2 A/C, 2 air handler, 1 boiler, 2 AC wall units and duct work that was installed by a hack. F***** up attic, blocked main panel just to name a few.

Sorry I am going off the deep end.

Why so many AC units for such a small house?

They left the hot water boiler as the source of heat.

But with the amount of ductwork, air handlers and outside condensors it would of seemed to me that a conversion to one heating and cooling system would of been the way to go.

Here are a few pics for your enjoyment.

Lets see they F***** Up a lot.

Damaged the insulation. Obstructed the main panel. Did a lousy job of sealing and supporting flex ducts in attic. Did not connect attic handler driptray to condensate pump, blocked the bathroom exhaust fan and a whole lot more. I had to fight through a small area to find what I did.I would imagine the attic wiring is in need of repairs. This same hack must of done the electrical too.Used copper water pipe to support about 8 wires.

The condensate discharged on the roof, the drip tray would discharge directly on the attic hatch. The provided no cooling/heat source in finished basement family room. This job was anything but Cool. Was nice of them to leave fittings and glue/primer.

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Better you than me. LOL

Thanks Mike I see how you are!!

This small 1300 sq. ft. house took me 4 hrs to inspect and 2 1/2 hours to do the report. To many oddities to have in vocabulary.

Well fellows , i see white on the brick which probably from condensation . i would say it isn’t lined Any thought

Here is a decent video on a liner install. (Even insulated)

Pretty cool David, thanks. :):smiley:

Mike next time you should open the cleanout and take a picture up to the top.
One with flash and one with out.

i had a pie pan cleanout in a 1925 wood frame house that was all corroded and the chimney filled with corrosion.
The flue most likely ends in the bottom and the flue gasses are eating the masonry Mike.

On a mid -effieciency furnace such as I had today the flue gases are corroding the chimney from the inside out.
I am guessing that if you went in the attic today ,you also saw efflorescence there too.

To bad you did not get a shot looking down the chimney,as I never got on top of my Gambril roof .

i can share some photos later but I am doing the report on the road as I am tripping for the weekend and going to Cheese Head territory.

Lucky me will have wifi and upload my shots there.

Mike all the old houses have cleanouts.


Mike stated in his original post that the access door was stuck closed.

I try to open and take pictures as you stated but many access doors are blocked or stuck as they have not been open in a long long time.

Or they fall out like this one did. :smiley:


Mine today was just a piece of rust and fell apart as I pried it.
Sorry I missed the stuck part as I had just walked in and dead tired.

The chimney in the photo has a clay flue/liner. The condition of that liner is what is in question. When the furnace was changed to a higher efficiency model, it may or may not have caused condensation inside the flue. Regardles, ALWAYS state that you cannot see the entire length of the flue and recommend a Level II inspection be performed by a certified sweep.

Regardless of what you may be thinking… ALWAYS call for the Level II.

The clean out door was stuck shut.