I am installing a Heil 90%+ 100,000 furnace and I'm told that I must have a 3" PVC flue. The intake and exhaust are both 2" and the installation manual doesnot say where the 3" is to start and end. To get the the outside wakk is less than 15 feet and has to have 2 long 90's and 3 45's in the run. all this accure in the first 6 feet. The straight run from there is 10 feet. If I run only 2" the distance the draft switch will not close. One HVAC mech told me all I have to install is a section of 3" in the run and finish with 2" comb intake/exhaust fitting through the plate to outside. Thank you for your time, Don

Follow the manufacturers instructions that came with the unit EXACTLY.

I agree with the tech you talked to run the 3 inch pipe, It will be increased from 2 to 3 at the furnace and reduced through the termination kit at the exterior.

The correct venting for a Heil ( ICP) furnace at 100,000 input is 3 inch increased right after the 2 inch comes out of the furnace cabinet with an increaser... and 3 inch ALL the way through to the outside of the home!! NOT reduced again to make the way through the siding of the house... check the install manual that comes with the unit... it is shipped with the furnace... and left in the blower area of the furnace along with the rest of the installation parts...

Thank You this solved the problem. The book was not in the furnace.

My bad. Heil is one of the ones not using a termination kit yet.

Just for your information... the Heil ( ICP ) concentric kit for 3 inch is a NAHA001CV they have had this kit for a long time now, nice looking termination... many people do not know about it... It looks much neater, with on pipe showing outside... And for the people out there who may need the 2 inch kit, for any furnace UNDER 100,000 btu/hr rating it is a NAHA002CV... TSA7MAN

An added note, be SURE to slope the exhaust vent pipe back to the furnace at 1/4 inch per foot slope, and make sure all of the exhaust PVC vent is properly secured to prevent sagging when it warms up from use! Condesation must drain back to the furnace trap do be able to drain it. You can go to the wwwgoheil.com web site and find the install manual under the technical section ( new products and section for furnaces, then look for install manuals, find your model number, which is listed on your furnace ID tag)... tsa7man