Best pro flue-to-chimney connector?

Motorapido

When heating season ends, I intend to replace the flue pipe from my Peerless gas boiler to and through the chimney junction. This is not a high-efficiency boiler and it connects to a brick chimney that has no stainless liner, but my chimney inspector says the tile lining is in excellent shape. This is a natural atmospheric system and not a fan-forced exhaust. The flue currently passes through the concrete block basement wall and into the chimney and is sealed with the typical messy high-temp flue sealant material. The sealed area around the flue pipe and masonry opening is a bit cracked now, but still in pretty good shape. Regardless, I want to replace the flue pipe and make a nice clean connection at the masonry opening. Is there an elegant solution? I'm thinking of a flat metal plate with a hole for the flue pipe and a flange, with the flat plate sealed to the basement block wall at the chimney hole opening with high-temp sealant and held in place with masonry screws, with the ability to remove the flue pipe from the flat plate's connector flange by taking out sheet metal screws, to allow for easy inspection and cleaning of the bottom of the chimney. This would make a tidy installation and prevent the cracking and crumbling of the typical type of masonry sealer that you usually see around flue pipes where they enter chimneys. I've googled around but seem to find solutions intended for wood stoves. On a related note, would there be any advantage to using double-wall flue pipe coming off the boiler? The boiler sits very close to the masonry wall and chimney connection, but even so, it seems a double wall flue would retain more exhaust temperature, allowing for a healthy draft. Please share applicable knowledge. Thanks.

HVACNUT

What size is the flue on the boiler?
If 6", when I did installations, I would put a 7x6 squat reducer into the breach. Steel wool is good for filling the corners and a nice coating of furnace cement.
It's no Monet, but it looks good and is easily serviceable.

Bob Harper

I recommend you leave this to a chimney pro. Your suggestions illustrate your lack of understanding the codes or problems. The vent or chimney connector is not sealed where you think it is. It must be sealed flush with the inner wall of the flue. You cannot cement galvanized pipe into a wall anymore-it can be installed into a thimble or sleeve that is properly cemented to the face of the flue. Still, the chimney must be suitable for the class of service. I can't remember the last year I found a masonry flue that was and I'm a professional certified chimney inspector. Reline it. If oil, it must have a cleanout. Otherwise, sweep it into the room then connect your unlisted single walled vent connector. A liner would get cemented into the wall and solve all your concerns about how to treat the wall penetration. Moreover, it won't disconnect killing the occupants. Please contact a chimney pro and have him run a video camera down the flue so you can see the failure of the mortar joints and degradation of the flue tile.

Motorapido

Thanks, Bob. I do appreciate the need for following code and the need for chimney inspection. However, the home inspector I hired before buying the house noted that some additional patching should be added around the galvanized flue pipe, which simply passes through the unlined (no thimble) concrete block wall, where it extends 1/4 inch or so into the bottom of the brick chimney. He said it is not a big deal in the short term since the condition is a little cracked but mostly fine, and that I could just build up the sealant at some point. The same conclusion was drawn immediately after I moved into the house and had the boiler/gas burner cleaned by the company that the prior owner had been using (pretty big local outfit). They said, "Don't worry about it for now, and within a year or so just patch it a little." I didn't get around to it, and a new contractor I hired for this year's inspection and cleaning said the same as the last contractor, which matched what the inspector had told me. Based on that, I planned to do the job when heating season ends, but just wanted something more cosmetically perfect looking than sealant/cement spread around the pipe at the block opening. Is a thimble required for penetration through a non-combustible block wall when the opening goes right into the chimney?
The original home inspector when I was getting ready to make an offer on the house eyeballed the inside of the chimney and declared it to be amazingly pristine on both the fireplace side of the flue and the boiler side. Granted, he was a general inspector, and just looked inside with flashlight and mirror in hand. I then hired the area's biggest chimney sweep/chimney inspector/chimney liner to do a thorough, pro inspection and to tell me if a stainless liner would be a good idea. That chimney specialist marveled that the interior chimney tile was in excellent condition for a 1920s house and said it would not be worth spending the money to line it. He said, "Your 10-year-old boiler will likely fail long, long before the chimney interior begins to deteriorate enough to need lining. At that point, replace the boiler with a direct-vent model through the foundation to the outside, bypassing the chimney. Forget about lining the chimney." I appreciated the fact that he talked me out of spending money with him. Am I missing something here? He also said the same advice about just adding some chimney/flue joint patch where the flue goes through the block wall, like all the others had told me. Have all these opinions been off base?

Jamie Hall

I doubt that your various inspectors' opinions have been much off base. Yes, it would be nice to have all the fancy linings and all, but if you have a good chimney person inspect the thing and pass it... stop. As to the cosmetics... well, that's your call.

Tim McElwain

Listen to Bop Harper he is right on and remember carbon monoxide is a silent killer. Thimbles are the only way to pass flue pipe through an existing wall.

As someone who has worked in the gas industry for over 50 years, and for a gas utility in the days when that meant something do it right!

HVACNUT

Unless I'm not understanding, the OP is only concerned with aesthetics. He very simply has a horizontal flue entering the breach via a concrete foundation wall. No need for a thimble. If it's penetrating through flammable material, then yes, a thimble is needed. But concrete, no. Also no need for a liner unless necessary.

Bob Harper

A home inspector is unqualified to comment on the suitability of a chimney. They are not trained to inspect the interior of chimneys nor are they required to by their industry Std. of Care. A visual inspection alone is inadequate to determine the suitability. You can only see a few feet in either direction. Liners are also indicated for sizing or to solve cold backdrafting chimneys. A thimble can be simply a terra cotta round flue tile or steel sleeve inserted horizontally until it is cemented to the inner face of the flue. It must be surrounded by 12" of solid masonry units. This guy has hollow CMU block. The open cells in block act like chimneys and conduct heat up where it may contact combustibles, typically a mudsill and pyrolize it or convert it into charcoal, which has an ignition temperature around 250-300F. A vent connector must penetrate the entire wall and discharge into the flue-not into the wall as some here have advocated. No, it is not acceptable to attempt to glue the connector to the wall breaching with bubble gum or furnace cement. That's how people wake up dead. It must be a positive connection. Why are so many HVAC techs so resistant to doing things properly? These things are put into codes for good reasons. I know: I sit on the NFPA 211 Technical Cmte. and UL 103 Standards Technical Panel. We don't write code just to inconvenience people. If you don't understand why something is in the code go seek answers instead of scoffing at it.