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Unlined flue?


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I'm looking to see if I could get some clarification. I did an older building yesterday that had an interior flue that vents the Cat1 furnace and water heater made from chimney blocks.

I couldn't get on the roof because of the snow, but there was a small opening at the base where I could see that it wasn't lined.

Most unlined flues that I see are made of single wythe brick, which is an easy call, but this block kind of threw me for a loop.

The Chimney Safety Institute defines a chimney liner as clay, ceramic or metal conduit, so I think I have my answer, but I want to check here just to get other opinions just to make sure. Am I correct? This flue is unlined? Thanks for your help

Tony

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I'd like to see the water heater that's made of chimney blocks.

Since you didn't really get a look at the business end of the stack, you really don't know what's going on. Shouldn't you suggest a thorough chimney inspection using whatever means necessary to ascertain that the chimney is safe and reliable?

Be prepared to explain why the chimney person can get on the roof to inspect and you couldn't

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...what I have heard called "flue block". I don't see why a liner is needed if the venting is only for gas furnace/appliance.

A solid fuel chimney would of course want clay liner as well as a clay thimble at the connection.

I guess why I'm having a hard time with this is because of the furnace. Category 1 gas fired furnaces aren't allowed to vent into an unlined flue. Would a flue made of this block considered to be lined?

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Tony, you're overthinking it. It's completely reasonable and smart to indicate there should be a liner in any masonry combustion gas vent, regardless of the building material.

Any mildly competent heating tech will tell you a liner is, at minimum, desirable, even if they don't say it's "required".

I always tell folks to put a liner in these things. If someone finds a moron that says it's not required, that's their prerogative. Their prerogatives do not change my opinion.

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The blocks used for that chimney are intended to contain a terra cotta tile liner. There's no doubt that chimney needs to be lined.

When I can't see the interiors of chimneys any other way, it's amazing how often vent connectors just happen to come apart all by themselves (when nobody is looking).

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I have a picture of an unlined concrete block chimney with creosote bleeding out thru the concrete.

I remember a guy in the '70's, yep I do recall, [:)] he installed a concrete block chimney, no liner, and hooked up a woodburning heater. In less than one year, that chimney was black with creosote, bleeding thru the concrete.

A few years later, I built a similar chimney but installed the masonry flue liner. It is still in use, wood heat, AFAIK no problems whatsoever in 30 yrs.

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When I can't see the interiors of chimneys any other way, it's amazing how often vent connectors just happen to come apart all by themselves (when nobody is looking).

Exactly. That top water heater connector looks like it would come out easy.

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Tony, you're overthinking it. It's completely reasonable and smart to indicate there should be a liner in any masonry combustion gas vent, regardless of the building material.

Any mildly competent heating tech will tell you a liner is, at minimum, desirable, even if they don't say it's "required".

I always tell folks to put a liner in these things. If someone finds a moron that says it's not required, that's their prerogative. Their prerogatives do not change my opinion.

Thanks to you and everyone else for your response. You're right about the over-thinking part. I'm usually not like this, but for some reason this job got to me.

The buyer is a single 20-something year old woman, 1st time buyer, buying a 110 year old flip, which was kind of a mess. She had no idea what she was getting into. I'm not sure what the RE agent was thinking, showing her this place.

Tony

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Tony, you're overthinking it. It's completely reasonable and smart to indicate there should be a liner in any masonry combustion gas vent, regardless of the building material.

Any mildly competent heating tech will tell you a liner is, at minimum, desirable, even if they don't say it's "required".

I always tell folks to put a liner in these things. If someone finds a moron that says it's not required, that's their prerogative. Their prerogatives do not change my opinion.

Thanks to you and everyone else for your response. You're right about the over-thinking part. I'm usually not like this, but for some reason this job got to me.

The buyer is a single 20-something year old woman, 1st time buyer, buying a 110 year old flip, which was kind of a mess. She had no idea what she was getting into. I'm not sure what the RE agent was thinking, showing her this place.

Tony

Yep That question has passed thru my mind a few times as well, why this place? Probably because of the new kitchen. But we don't know what the circumstances are, sometimes the single lady turns out to have 3 boyfriends that are builders. [:)]

I had a similar house a few months back, and just labored away at describing everything without putting prejudice or judgement in there.

They had laid new flooring right over the ugly return air ducts. The new siding stopped at the ground level, but the rotten skirting carried on down for another 2 feet. They had shoveled vermiculite into piles on top of fiberglass to get access for pot lights. She walked, but I never said she shouldn't buy it and fix it.

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  • 2 months later...

Chimney block are just a simplified way of meeting the minimum 4" nominal masonry unit chimney thickness. However, ALL chimneys must be lined and has been a code requirement since 1927. The chimney must be suitable for the class of service, too. The flue must be properly sized for the attached appliances. Since this is an interior chimney, it should have a 2" clearance to combustibles and firestopping at each floor/ ceiling.

In the photo provided, the vent connectors are not properly supported, are not properly sealed to the chimney, do not appear to have a thimble or sleeve and there is no cleanout 12" below the breeching.

A Level II inspection is triggered here per NFPA 211.

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