Thread: Flue connections

I just inspected a house where contractors installed a new flue vent in an existing masonry chimney. They were just finishing up and I didn't get a chance to speak to the contractors. The old flue is/was terracotta and don't know if they removed it or just inserted the new flexible flue through the old terracotta liner. Also don't know what the reason was that required the work. Buyer is not aware. Seller is gone.

My question: Does the connection where the appliance vent (combined furnace and water heater) is inserted into the new flex vent need to be tight with no voids around the opening? See photos. There is a nice gap around the connection. I was going to write it up with a comment that a tight-fitting collar is necessary. The water heater vent is minimally pitched at barely 1/4" per foot.

Your thoughts and comments?

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It's called a 'chimney liner'. The part sticking out of the wall appears to be a mortar sleeve that protects the liner but has no function in containing flue gases.

The foil tape needs to come off the joint--not allowed and unnecessary.

The liner enters too low. No vent rise off the WH. Will be prone to spilling flue gases out that draft hood.

WH connector needs to be larger.

Professional needs to verify the size of the liner. If you add up the input BTU/hr. and vent height then look it up in the tables, it will tell you the 'common vent' size for that height. Then de-rate it 20% for corrugated liner plus another 20% if it offsets.

If that furnace is also gas, the liner should have entered about 6-8" below the bottom of the floor joists. Just because the original breeching was made too low by the mason doesn't mean everyone else has to live with it.

The connector is not supported.

Make sure three screws min. per joint, seams up, and pitched up 1/4" per foot.

What does the liner termination look like?

Bob....

OK, I now see the sleeve and why it's there.

1. Why is the tape not allowed and unnecessary?

2. Why does the WH connector need to be larger? It's also combined with the furnace heater.

The termination has a new flue cap but not sure how it was installed. I will try to go there again for another look.

This is a very helpful reply. Thanks.

I would think that the sleeve should be sealed even if it is not code.

The 90 above the water heater is very close. 6" is required before a bend can be installed. Where the measurement is taken from I am not sure.

Originally Posted by Stanley Chow

Bob....

OK, I now see the sleeve and why it's there.

1. Why is the tape not allowed and unnecessary?

2. Why does the WH connector need to be larger? It's also combined with the furnace heater.

The termination has a new flue cap but not sure how it was installed. I will try to go there again for another look.

This is a very helpful reply. Thanks.

Tape is covering vent connector, which is not allowed. Pipe must remain exposed for visual inspection. Any connector material must be non-combustible. That tape has not passed ASTM E-136, therefore, it must be treated as 'combustible'. What is the tape doing? There is no need to seal CAT I venting since its under negative vent pressure.

The connector should be upsized for performance and because its in the gas code sizing tables. If that WH had more than 3 ft of vertical vent rise, it would be another story. Those charts all start with a min. 12" vent rise, which you don't have.

You can seal that sleeve and probably should. I just wanted to point out that the seal on combustion gases is to the liner-not the sleeve.