Fundamentals: Furnace Vent Sizing

December 20, 2001
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The problem: Replacing an existing gas furnace with a new, more efficient furnace.
The apprentice: Allen Charles Edwards (ACE) — First-year mechanic.
The technician: N. Arthur Thomas Egan (NATE) — 15-year veteran.

NATE and ACE are working together to replace an old gas furnace with a new gas furnace. The new equipment is more efficient than the system being replaced.

NATE: “ACE, please get the stovepipe out of the storage area.”
ACE: “What?”
NATE: “Go check the installation literature so we take the right supplies to the job.”
ACE: “Uh, NATE, I can’t find the information on a stovepipe in the literature. It does talk about using materials that are good for Category I appliances.”
NATE: “ACE, I hate to admit this, but when it comes to the new furnace venting, I always have to refer to the code book to make sure I’m not incorrect in selecting materials. Let’s get the code book out of the truck and make sure we have the proper materials. We can then look up the Category I information.”
ACE: “I have the code book. Can you tell me what category each falls into?”

1.
ACE: “An appliance that operates with a nonpositive vent static pressure and with a vent gas temperature that avoids excessive condensate production in the vent.”

a) Category I
b) Category II
c) Category III
d) Category IV

2.
ACE: “An appliance that operates with a positive vent static pressure and with a vent gas temperature that avoids excessive condensate production in the vent.”

a) Category I
b) Category II
c) Category III
d) Category IV

3.
ACE: “An appliance that operates with a positive vent static pressure and with a vent gas temperature that may cause excessive condensate production in the vent.”

a) Category I
b) Category II
c) Category III
d) Category IV

4.
ACE: “An appliance that operates with a nonpositive vent static pressure and with a vent gas temperature that may cause condensate production in the vent.”

a) Category I
b) Category II
c) Category III
d) Category IV

NATE: “Well, while we have the code book out, we’d better make sure of the material that is allowed for this Category I appliance venting.”

5.
What material is allowed for venting Category I appliances?

a) Single-wall metal pipe
b) Type B gas vent
c) CPVC gas vent
d) PVC gas vent

ACE: “Just so I know, what is stovepipe?”
NATE: “It’s a single-wall metal pipe. I’m glad you keep me on my toes, ACE.”
ACE: “We’ll have to go to the supply house and pick up the material. We’ll read the rest of the installation literature on the way to make sure we get the right size, not just the right material.”

Next month: NATE and ACE will determine and select the right size of the Type B venting material.

Answers: 1. a) Category I, 2. c) Category III, 3. d) Category IV, 4. b) Category II, 5. b) Type B gas vent.

Patrick Murphy is director of technical development, North American Technican Excellence (NATE). If you have any further questions or comments on this Fundamentals quiz, contact Murphy at pmurphy@natex.org (e-mail).

Publication date: 12/24/2001

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