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I have a category IV furnace. make up air venting??

I have a category IV furnace. I am using a 2 pipe venting system. building inspector says i need a make up air vent. he won't give me a specific code for this. anyone know what he is refering too? the furnace is a 90+ with a sealed air intake from outside. local jurisdiction is cincinati, ohio

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  • tellrob Sep 28, 2009

    thanks for the reply terrencio,

    this is a 100 year old 4 unit apartment building (loose). we are replacing a central boiler with high eff furnace units in each apartment. each unit does have a gas range. hot water is heated by gas water heater in the basement.

  • terrencio
    terrencio May 11, 2010

    Well I am not familiar with the local codes for that region (I work in Canada). You are right the two pipe cat IV does not require make up air as it provides it's own. That being said what type of construction is the home, loose or seal (R2000 standards). and what other fuel burning appliances are in the home, eg water heater, non-direct vent fireplace...etc? My feeling is if the inspector cannot be specific about the issue, then he's blowing smoke to cover his *ss.



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You're beating your head against a wall! Just do what the inspector says or he can make life very hard. EVERY house needs fresh air!

Posted on Sep 26, 2009


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Hi Missy:
Your question is in the cars and trucks section, but it sounds like it is about your home ventilation system.

I'm thinking that you probably have an HRV (Heat Recovery Ventilation) system that you are asking about.
- Even in the non heating seasons, these units are intended to operate for 20 minutes of every hour, when humidity gets high, or when a manual timed switch is pressed for bathroom exhaust fans.
- Inside air from the bathrooms and possibly kitchen is sent through the HRV to the outdoors.
- Fresh outside air is drawn in through the HRV at the same time and distributed throughout the home via the vents you are referring to.
- These devices are designed to improve air quality in the home, AND to reduce costs in the heating season.
- Additional devices like furnaces, air conditioners and heat pumpscan be part of the system so it can get complicated.

-If possible, I would be trying to check with the builder of your home to find out what system had been installed.

Hope this helps.
Ted (Retired Building Inspector)

Jul 06, 2015 | Cars & Trucks

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Does my furnace require outside air?

I'm surprised the building inspector allowed the condensing furnace you described draw combustion air from the garage !! I'm not familiar with any manufacturer that recommends that as normal practice. Virtuall ALL two pipe condensing furnaces require both pvc pipes to be terminated OUTSIDE the structure with specific heights and distances apart. There is also a limit to the length of both the flu and the combustion air piping and each 90 degree pvc elbow adds the resistance equivalant of roughly 10' of straight pipe. If re-routing is required, you have to bear in mind the direction of 'fall' in the piping usually goes back towards the furnace and remember two 45's may give you a greater variance of change in the piping and still be equal to the equivalant of one 90.

Personally, I would never suggest terminating the fresh air (combustion air) intake between floors of a structure.

Jan 02, 2015 | Carrier Heating & Cooling

1 Answer

I have a concentric vent on my furnace. I put a vent cap on top because it goes there the roof. I am getting water in the furnace fron the fresh air intake. I can't seem to find out why. Could the

most concentric vent kits do not have a cap on the exhaust termination. if they do they are usually approved for use with that particular vent kit. most of the concentric vents i have seen have terminated through the side wall of the house and have no "rain cap" on them. if the cap you put on the vent is one you "home made" then you need to remove it and get one that is approved for use on your make of vent. I suspect that the water you are getting running down the air intake part of the vent may be water that has condensed from the exhaust fumes. If the cap is an approved one then you may have a leak in the exhaust pipe section of the vent and I would suggest you call an expert in to verify the integrity of the venting system

Oct 07, 2012 | Noritz 196105 2" X 28" Concentric Vent Kit

1 Answer

My son has condensate building up in his flue and running down into the furnace. It is a 2 stage furnace. The contractor who installed it blames it on the chimney. Is that likely?

It is for sure a venting issue, depending on where you are located, it sounds like the local building code inspector was not involved for an inspecton of the furnace replacement. When the flue condensates like that, it is usually because the flue is the wrong size, usually to big,or it is dumped directly into a masonary chimney, and the chimney was not lined to the top.
I hope this answers your questions, please rate me and let me know if I can help further.
Paul Gibson

May 13, 2010 | Goodman GMS90703BXA Heater

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What to do with exhaust pipe to close to house and freezing up door and house. exhaust pipe comes out of the wall from furnace in basement 12inches and on this pipe is a tee vented on the top and the...

Best solution is to put a reducer instead of the tee this is recomended by some companies to increase velocity of exiting gases. If you increase the length this will have a affect of icing in the pipe. Try the reducer if its 2" reduce to 1 1/2" or 3" reduce to 2"

Best regards,

Dec 15, 2009 | Coleman Heating & Cooling

1 Answer

Furnace not blowing hot air but cold, gurgling sound from the unit, likely condensation lines.

It sounds like a vent pipe sagged or the condensate drain trap is plugged.
You did not say what make and model furnace you have so I'll have to give you some generic intructions.

(1) Find the condensate trap and pull a plastic hose off of it and blow it out as best you can. Also you can pull the bigger hose that most furnaces have at the bottom of the heat exchanger off and blow through it.
Check all of the hoses to make sure that they are not plugged or filled with water. Methodically go through each one carefully pulling and replaceing exactly where they came from. Do not just pull all the hoses and expect to remember where they came from.

(2) Check the intake and exhaust pipes, assuming that this is a two pipe furnace. If there is water build up in the exhaust pipes the furnace will not operate.
Check for places that the pipe could be sagged or trapped. Even a sag will allow enough water to pool in the pipe and stop it.

I hope that this will help you to solve your problem!

Thanks for using Fixya!!


Dec 10, 2009 | Heating & Cooling

1 Answer

Colman mobile home gas furnace to use in my garage/shop

generally speaking a sealed combustion system is inherently more safe than a system that draws it's combustion air from it's ambient location. however, it cannot be considered 100% safe in a potentially hazardous location. The actual system that would be used in a "code compliant" installation would be a 100% outside air unit.
That being said, you can install this in a garage, the vent that you are referring to (if it is a standard mobile home system) is generally directly above the unit and usually no longer than about five feet. It also requires a listed and labeled termination "cap" If you install 90 degree angles or extend the vent too far you will have issues with condensation in the piping that will cause the pipe/ heat exchanger to fail prematurely.
If the system is a 90+ efficeint unit then the PVC venting is generally allowed to be about 30 feet long, with a 1/4 inch per foot pitch back to the unit for condensation, also the general mfg. instructions allow either 2- 90 degree or 4 45 degree fittings in the line. hope this helps

Nov 06, 2009 | Coleman Propane Forced Air Heater...

1 Answer

Condensation running down old vent pipe running to roof.

This is a condensing furnace and is ment to condense. You will need to pipe away the condensate using a hose and maybe a condensation pump. It is unclear where the combustion air pipe is going? Are you using room air? or do you have a second pipe going up the old vent as well?

Jan 05, 2009 | Goodman GMS90703BXA Heater

2 Answers

Inspection troubles

If you google the make and model number you should pick up the company website where you can down load a manual .You may also find a tech helpline they will give the right size flue .

Mar 23, 2017 | Goodman Heating & Cooling

1 Answer

I am living in a home with a carrier furnace. The furnace is in the back part of the house in a store room. It has two- 2 1/2 inch plastic pipes. One that suppplies air to the furnace and the other is...

As long as the fresh air intake pipe to the furnace is not plugged up the second vent is not needed some homes when they are new are air tight and need a fresh air circulation system

Oct 30, 2008 | Carrier Heating & Cooling

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