Furnace flue

[David P. OKeefe]

Can someone with more knowledge help me out here? Is there a problem with this installation of this flue from this furnace? I looked at it and it didn't look right to me. The furnace is on the left and chimney on the right. Only about 4 feet from furnace to chimney.

[James E. Braun, CMI]

Does the furnace have an inducer draft motor?

[David P. OKeefe]

yes it does

[James E. Braun, CMI]

It looks like the water heater connects to the furnace pipe by a tee. If so, it should be a wye so the exhaust gases do not take the easy way out via at the water heater.

[James E. Braun, CMI]

Also if that is an opening a ways down below the metal flue on the chimney, it needs to be closed up for the chimney will create a better draft.

[Bob Elliott]

Why you should not reduce

If your appliance has a blower to assist with draft (most of the newer units do) you definitely want to reconsider reducing your pipe diameter.

When your appliance tries to push 35 Cubic Feet of air through an opening that was only designed to move 20 cubic feet, you are immediately faced with a problem. As most stoves are designed to solely to vent exhaust gases, this reduction in flue size forces the motor to act not as a blower, but as a compressor. As most integral motors are not designed for this function, you will experience severe wear and tear on all moving and stationary parts, often voiding your warranty and requiring early replacement of the unit.

Keep in mind that most manufacturers of pipe do not even fabricate or produce any type of reduction collar for these reasons

[James E. Braun, CMI]

The pipe is enlarging as it is going to the chimney, not getting smaller.

[Jeffrey R. Jonas]

Originally Posted by belliott

Why you should not reduce

If your appliance has a blower to assist with draft (most of the newer units do) you definitely want to reconsider reducing your pipe diameter.

When your appliance tries to push 35 Cubic Feet of air through an opening that was only designed to move 20 cubic feet, you are immediately faced with a problem. As most stoves are designed to solely to vent exhaust gases, this reduction in flue size forces the motor to act not as a blower, but as a compressor. As most integral motors are not designed for this function, you will experience severe wear and tear on all moving and stationary parts, often voiding your warranty and requiring early replacement of the unit.

Keep in mind that most manufacturers of pipe do not even fabricate or produce any type of reduction collar for these reasons

Bob,
That is an "increase", not a reduction in size. Flow is from left (HVAC) to right (chimney).

[Bob Elliott]

Look again as it reduces at that collar or are you not looking straight.
First it constricts at the join point of that connector for no apparent reason.

Do you not see the angle on the green lines I drew.

The volume of air is restricted by at least 20% at that point.

This is not an A/C line expansion device as far as I can tell.

[James E. Braun, CMI]

The pipe coming from the furnace looks like a piece of B-vent to me, if so then there is no reduction. It just looks that like there is a reduction.

[Jeffrey R. Jonas]

Originally Posted by jbraun

The pipe coming from the furnace looks like a piece of B-vent to me, if so then there is no reduction. It just looks that like there is a reduction.

Agree, looks like (double wall) on left, increasing towards (single wall) of larger diameter on the right.

Look at the second pic. The outside diameter on the left is smaller than the outside diameter on the right.

My guess is a 3" or 4" ID up to a 5" or 6" ID.

[David P. OKeefe]

I thought it reduced in size at the connection and why I asked for assistance. Just my eye playing tricks on me. B-vent into a single wall.
That cleanout is for the fireplace chimney.

[Gary Reecher]

It is best to have a 12 inch rise before adding an elbow on water heaters, most manufacturers require at least 6 inches. Looks like that one has none.