Do I need a chimney liner when I install an 80% gas furnace that has a clay chimmney?

Do I need a chimney liner when I install an 80% gas furnace that has a clay chimmney?

Yes

We had to have one. Code required it.

The furnace will give off an acidic moisture ladden exhaust that will deteriorate your chimney. Like HVAC says, yes.

First it is up to your state code, In New York State, you do not need a chimney liner if the chimney has a clay pipe liner. Refer also to the install manual for a 80 % furnace. You can alson refer to the NFPA 54 Fuel gas code, but YOUR state code of your state rules over all specifications... call your local building / code inspector for further information.

(((First it is up to your state code)))
Incorrect. The manufactures install instructions override all others. This is protocol in all 50 states and Canada.

The fuel gas code and any other manuals dealing with HVAC is subservient to the manufactures install instructions.

Now why is this?

Many years ago it was decided to use the manufactures install instructions. Who else but the manufacturer with all the testing and approvals (CSA/UL) would no best as to how to install there equipment safely.

Well, I disagree that the manufactures install instructions are over any state code, as a past code inspector for 18+ years, the state code and AHJ ( authority having jurisdiction) has the final say over any questions on the applications of any heating appliance under the "STATE" fuel gas code. (An added note here, ICP's install manual for their 95% furnace has an insert into their install manual where the State of Massachusetts has a different requirement for venting the unit, which you must comply with in that state, which is totally different than the install manual directions.) NFPA 211 standard for chimneys section 7.2.2 states that masonry chimneys must be lined, and types of liners depending on appliance including clay flue liner. If you go to ICP's ( Heil Tempstar and Airquest ) 80% furnace install manual section 7 under "masonry chimney venting, and their flow chart, you will see that the chimney must have either a clay liner, or you have to line it, which also states that it must conform to any state or local codes. If you go to the NFPA fuel gas code 54, and look at venting sizes for chimneys, the New York State fuel gas code is MORE restrictive on vent sizes and the equipment is inspected to that tighter requirement, due to the colder weather in the Northeast, and that causes venting issues. So, if we have any building / code inspectors on this site... kindly add your comments as well.

The installation instructions will determine what goes on, as the National gas code is not updated as frequently as technology develops. Follows is an excerpt from the venting tables of a Carrier furnace:

All requirements contained in this booklet apply to both Category I drafthood equipped central furnaces as well as fan-assisted combustion system central furnaces. At no time should a venting system for a listed Category II, III, or IV central furnace be sized with these tables. *The National Fuel Gas Code (NFPA 54/ANSI Z223.1-1988) may also be used to size venting systems for drafthood equipped central furnaces. However, at this time, the
National Fuel Gas Code does not include alternate sizing methods for fan-assisted combustion systems. Therefore, until engineering data is developed to allow alternate sizing methods for Category I fan-assisted central furnaces, the enclosed venting tables must be used for fan-assisted combustion system central furnaces.*

So here you have the manufacturer saying "the codes aren't up to snuff to our new stuff-here's how to do it." RTFM, my friends... read the fine manual. LOL.

Frdbrkl, very good point. I guess the bottom line is you go with which ever is the most strict.

The bottom line is the vent must remove the carbon monoxide gases, the vent must remain hot to cause the gases to rise up the flu and out , these gases are heavier then air and once cooled they will fall back. A clay chimney requires a great deal of heat to warm it up and the newer furnaces 80 and 90% furnaces have less heat going out the vent to carry the gases out, if this chimney is dedicated to the furnace only I suggest installing the type and size called out by the manufacturer. Good luck, Mike

Usually the only information a installer has is the manufactures instructions. This point was made very clear to me back in 1983 when I broke in to the inspection stuff. Since I was in the field installing for many years I thought that all that time I was doing wrong when I looked over all the 3000.00 worth of manuals in the state office. After a chat with a very well respected inspector his statement was simple to me.

Inspectors do not get sued unless they just plain do not show up for a inspection.
Inspectors are always to follow the manufacture instructions since even the NEC is only changed every 3 years and cannot possibly keep up with technology.
The installer has only one book available to them in the field and that is the manual for the item they are installing.
The manufactures put these manuals in there equipment for a reason.
If the equipment is installed to there specs it will work properly and the warranty will be kept in effect.
The manufacturer is the deep pocket here and lawsuits will be filed against the manufacturer.
If you fail to install or inspect to the manufactures manual/plans/drawings you then become a second target.

I really loved the inspection work I did. It was kind of like they paid me to drive around in a new truck and visit all my friends. LOL
There were some times we had to tag for wrong doing but it was usually the dirt bag installers or the do it yourselfers who came under close supervision.

It always took 3 times as long to inspect a do it yourselfer because it took forever to write up all the violations.LOL

GREAT answers from all of you and my hats off to Frdbrkl... install to the MOST strict code / requirements! Safety to the home owner is the most important point to ALWAYS consider. Thanks to you all, that's what makes this a great site. tsa7man

Doesn't matter what anyone here says. You go by what your inspector says. Being a HVAC installer for 20 years, life is easier to appease them rather than argue why you are right. That being said, it depends on your state codes.(The only time an inspector will refer to manufacturers specification, is if no code exists to cover said item.)