As an Internachi student I was inspecting my own gas furnace that is located in an unconditioned attic space. The bathroom vent that terminates at the roof is insulated. The gas furnace vent duct is not insulated. Should it be? If not, what is the rationale on that.
Thanks for your help.
Mikah
Got a photo? And are you speaking of the exhaust vent pipe?
Also, find the model number and look up the manufacturer installation instructions, they will give you a ton of information you need to understand.
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Assuming that your furnace vent is a double walled b-vent, that would be sufficient to prevent condensation which is why it’s required on your bath vent.
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Edit: No, if it’s a B-vent it’s not needed.
How? Cooling of gases causes the condensation. Not keeping it warm.
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You’re right, I had it backwards. Isulation would help prevent condensation especially in cold climates.
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Absolutely not. If it is B-vent, it needs clearance from combustibles. Insulation is considered combustible. If it is PVC, then there will be (or should be) a condensate management system built into the furnace and drain for said condensate.
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Image of, manufacture, model and serial numbers, if applicable please.
Questions. What gas fired furnace vent pipes are you referring to?
Combustion fresh air intake?
Exhaust flue?
Flue pipe materials?
Gas fired furnace metallic exhaust flues need to be protected from corrosion and condensation.
Awaiting your reply.
The flue material is not the deciding factor if a condensate drain should be present or not. You can have other materials used in high efficiency appliances. Stainless steel being one.
That’s true. But if it’s PVC, it’s definitely a condensing unit. I’m not sure if the OP ever stated the material.
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The only insulation you will see in a residential system is double walled vent. That is to protect objects that may come in contact with it. The furnace gas is too hot to condense in the short run to the exterior. When the furnace is off, there is a natural convection that removes moisture during the off cycle.
A bath vent is just above ambient indoor temperatures, with very high moisture per pound of air. It will condense as soon as it enters the unconditioned space. When it is off, it’s off. The fan stops all air flow inside the vent.
If you look up the wet bulb temperature of the air in both vents, you will see the difference.
