Venting High Efficiency Furnace into Existing Chimney

Home Maintenance Questions and AnswersCategory: Furnace VentingVenting High Efficiency Furnace into Existing Chimney
Question by Salik Alvi

I have a house that has a gas based water heater and the flue from the water heater is going into the chimney, I just removed the old forced air furnace and put in a new energy forced air furnace gas based, but I ran the PVC that takes the carbon monoxide out directly into the chimney is that ok?

1 Answers
Dariusz Rudnicki Staff answered 1 year ago

Hi Salik, Unfortunately, such installation is not permitted.
High efficiency / condensing type appliances cannot be vented through the same chimney as the regular type gas burning appliance. Condensation and exhaust gases temperature are the main issues.
There are two things you should do:

  1. high efficiency furnace requires its own, dedicated (no sharing with anything else) PVC vent that discharges through the side wall or house roof to exterior. There should be a manual that came with a furnace explaining proper venting of your appliance. If not, check the manufacturers website.
  2. Second thing is to make sure that your chimney isn’t oversized to vent water heater only – you’d need to find out its interior dimensions and the water heater draft hood diameter. Let me know if you have any problems…
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