Category III is defined as a gas heating appliance with a flue loss equal to or greater than 17% (non-condensing) with a positive vent static pressure. In a Category III venting system, if there is a leak in the venting system, flue gas will flow from the flue pipe into the space. Given the potential safety hazard of carbon monoxide building up in the space, Category III vent pipe must meet the additional safety requirements of UL 1738.
What is a Category 3 venting system?
Category III is defined as a gas heating appliance with a flue loss equal or greater than 17% (non-condensing) with a positive vent static pressure. In a Category III venting system, if there is a leak in the venting system, flue gas will flow from the flue pipe into the space. Click to see full answer.
What is a Category 2 appliance with non positive vent pressure?
The exhaust in the flue is gravity-vented. Therefore, its vent pressure is rated as “non-positive,” which is why it can be vented in common with a gravity vented water heater. Category II Appliances include appliances not typical intended for residential use.
What are the most common problems with Category I Vents?
Another potential problem with newer Category I vents involves furnace and water heater flues that are connected to masonry chimneys. In those cases, the cold masonry cools the exhaust gases, causing loss of draft, as well as moisture condensation. The solution is to use the masonry chimney as a chase for a B-Vent.
What is Category 1 venting on a furnace?
BE CATEGORY I VENTED. DO NOT VENT ANY OF THESE FURNACES USING CATEGORY III VENTING. Category I Venting is venting at a non-positive pressure. A furnace vented as Category I is considered a fan-assisted appliance and does not have to be "gas tight."
What is a Category 3 furnace?
Category III Appliances in residential use are mostly tank-less water heaters that are vented through the wall with stainless steel. These appliances operate with positive vent pressure and, therefore, cannot be adjoined to a gravity-vented water heater.
What is Category 2 vent pipe?
Category II is negative pressure, condensing. Category III is positive pressure, non-condensing. Category IV is positive pressure, condensing. These categories are used to determine the type of vent that should be used for the appliance.Jan 19, 2015
What is a Category 1 Vent?
Category I: The vent relies on gravity to get the flue gases out, and it's not a condensing appliance. If you poke a hole in the vent, air will go into the vent; flue gas won't leak out. Because of this, the joints don't need to be airtight.Sep 11, 2018
What category is B vent pipe?
Category 1 appliancesThe Category is actually applied to the appliance. The Category is actually applied to the appliance. B-vent is ONLY allowed on Category 1 appliances unless the appliance manufacturer has specifically certified a particular B-vent system to be used alternatively.Apr 1, 2013
What is a category 3 appliance?
Category III appliance - an appliance that operates with a positive vent static pressure and with the flue loss not less than 17%.
What is Type C vent?
Only type C vents are used. galvanized pipes are single walled galvanized pipes. Venting gas or oil is what they are used for. Toxic fumes can be caused by using a C vent with solid fuel appliances.
What is a Class B vent?
AmeriVent Type B gas vent uses a double wall of metal pipe for insulation and safety. The inner pipe of reflecting aluminum heats quickly, containing the warm flue gases inside. The airspace between the inner and the outer pipes provides insulation against heat loss to keep the warmer flue gases on the rise.
What is a Category 3 water heater?
Category III: The vent relies on a fan to push the flue gases out, and it's not a condensing appliance. If you poke a hole in the vent, exhaust gas will leak out. Because of this, the joints in the flue must be airtight.Sep 4, 2018
What are the two types of venting?
Active ventilation pulls the air in from the outside and pushes it out from the inside. Passive ventilation means the air in the attic is moved around by natural sources, such as wind. Both ventilation systems do their job, and one isn't better than the other.Apr 2, 2021
What is Category 3 flue pipe?
Category III is defined as a gas heating appliance with a flue loss equal or greater than 17% (non-condensing) with a positive vent static pressure. In a Category III venting system, if there is a leak in the venting system, flue gas will flow from the flue pipe into the space.Jan 19, 2018
Is Type B Vent double wall?
Type B gas vent uses a double wall of metal pipe for insulation and safety. The inner pipe of reflecting aluminum heats quickly, containing the warm flue gases inside. The airspace between the inner and the outer pipes provides insulation against heat loss to keep the warmer flue gases on the rise.
Why is it called B vent?
0:152:47B Vent vs Direct Vent Gas Fireplaces and Furnaces - YouTubeYouTubeStart of suggested clipEnd of suggested clipMeans you're inside pipe is exhausting. While the outside pipe is point fresh air from outside ofMoreMeans you're inside pipe is exhausting. While the outside pipe is point fresh air from outside of your home and bringing it into the fireplace for combustion.
How to determine if a vent is a Category I or III?
Whether a vent system is Category I or III is determined by the flue gas pressure in the flue pipe relative to the pressure in the space. However, it is not always clear what that pressure is since it is affected by the CFM of the power venter, length and diameter of the flue pipe, and pressure of the space the pipe is installed in. While two units may be installed in the same space, using the exact same vent pipe diameter and length, they may still be different venting categories. The unit installation manual may help clarify if the unit is only Category III or if it can also be installed in Category I applications.
What is a Category 1 gas furnace?
Category I is defined as a gas heating appliance with a flue loss equal or greater than 17% (non-condensing) with a negative vent static pressure. In other words, in a Category I venting system, if there is a leak in the venting system, air from the space will flow into the flue pipe and no flue gas will flow into the space.
What type of vent pipe is used for flue gas?
Since the flue gas is forced into the pipe, for almost all applications the flue pipe will be under positive pressure and require Category III vent pipe. The only exception would be in a commercial application if the space is under an high positive pressure or the venting system has a booster fan at the end of the flue pipe drawing the exhaust through it. In those cases, it would be possible for the flue pipe to be under negative pressure relative to the space pressure and would be Category I. Contact the appliance manufacturer to see if booster fans are allowed for use with their products.
What is the thickness of a single wall vent pipe?
Single wall vent pipe must meet NFPA 54, section 12.8 which requires the vent pipe be constructed of galvanized sheet steel not less than 0.0304” thick or equivalent material.
Can a hot flue gas vent be vertically vented?
For vertical applications: Since hot flue gas naturally rises, it is possible for the flue pipe to be under negative pressure even if the gas-fired appliance has a power venter forcing the flue gas into the vent pipe. If a manufacturer’s installation manual identifies that the standard combustion, vertically vented system can be Category I or III it will most like be Category I unless the space is under negative pressure. Conversely, separated combustion applications are almost always Category III regardless if they are installed vertically or horizontally. While they may still be installed vertically, due to the additional length of the combustion air pipe, the hot flue gas rising is not able to overcome the friction of the additional vent pipe. Check the appliance installation manual to see if vertical installations can be Category I.
Is a single wall vent pipe a B-vent?
Single wall and double vent pipe are designed to lock together and usually include an internal seal to help seal the joint. B-vent is not allowed since the joints do not form a gas-tight seal. Single wall typically will have a lower cost than double wall vent pipe. Double wall vent pipe, while more expensive, has a lower surface temperature which will reduce the clearance to combustible requirements. Consult the vent pipe installation manual for exact clearance requirements.
Is horizontal venting a category 3 appliance?
It should be noted that for residential appliances, all horizontally vented appliances are considered Category III regardless of the space pressure or booster fan. Per CSA bulletin “Gas Products No. 241” dated January 27, 2011, there is no residential horizontal venting Category I and all horizontal residential venting is to be considered Category III. Category I horizontal venting is only possible in commercial applications.
