HVACopediaTrane · Furnace troubleshooting
Freeze protection for vent pipe
What is going on
Vent pipe that runs through spaces below freezing has to be insulated, or condensate in the pipe can freeze and block the vent. Domestic water pipes that are not freeze-protected count as an unheated space, so check that before deciding no insulation is needed. Walk the whole run, including the part above the roof line.
Likely causes
- Uninsulated vent pipe in an unheated attic, crawl space or garage
- Exposed pipe above the roof line in extreme cold
- Space assumed to be heated when its water pipes are not protected
Check in this order
- Insulate exposed vent pipe in unheated spaces with 1/2 in thick Armaflex-type insulation or equivalent.
- Skip the insulation only where the space is heated enough to prevent freezing.
- In extreme cold, insulate exposed pipe above the roof line with Armaflex-type insulation.
- Check that the insulation is tight at joints and fittings.
- If the furnace has been locking out in cold snaps, inspect the vent for ice.
Applies to: All venting in cold locations
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Source: Trane installer's guide, p. 24, 23. Written in our own words; check the manual for your exact model.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.