how old is it?

IIRC, flues for woodstoves are/were double-walled. There was insulation between the walls. Age might determine what type of insulation they used.

It's a fairly new double or triple wall pipe, but the "stuff" was not between the walls, it was right in the middle of the flue. I was thinking that maybe the installer put it there to lower the temp. of the heater exhaust temp, but the heater temp is certainly lower than any wood stove. Maybe some of the insulation slipped down and is clogging the middle of the pipe. I'm at a loss as to what it is. I've had wood stoves in the past and nothing blocks the flue. I'm tempted to yank the stuff outta there.

Might be that someone put that stuff in there to close off the flue since the wood stove was removed.

Regardless, the flue should be clear to a top cap.

6" might be too large for the correct draw for a WH.

I know that the 6" flue is too big. The home inspector mentioned that to me. Seems to be working though.

I'm probably going to attempt to remove the obstruction. I might take a couple of pictures also and will report back.

Thanks.

"Seems to be working though"

It will seem to work fine until wind conditions effect the draw and cause vent problems for the WH.

Best to run the correct diameter vent up through the 6" and do it right.

Remember, diameter and length are a consideration for proper draw so it might be a good idea to consult a plumber to find out what you need to meet code.

Good point. First I want to get the junk out of the flue, then I can look into running the correct diameter pipe up the flue.

Here's what I found......a piece of insulation from who knows where.

Flue is now clear. Will investigate from roof end when weather clears.

culprit bagged and ready for disposal

Sano job on the copper and interesting that there's a ball valve on BOTH the service and return on the WH.

Who put the valve on the output of the water heater?

It is not allowed.

Whoever installed the heater for the previous owner of the house put the valve on.

Yep, someone put fiberglass insulation in the flue. Nice...
Have you noticed the headaches and feeling tired all the time?!?

Sounds to me like a CO detector should be located nearby.

Headaches, fatigue........nausea too! Only kidding.

Will be putting new CO detectors throughout the house very soon.

(Just yesterday, 7 people were rescued from an apartment building when their CO detectors went off when someone comitted suicide in car in an adjacent garage in the Baldwinsville NY area)