Orphaned Hot Water Heater article by Donn Anderson of Anderson Home Inspection LLC – from Waukesha to Milwaukee and all of Southeast Wisconsin
When someone replaces an older metal vented furnace with a new high efficiency pvc vented furnace, the flue gases from the furnace no longer leave the house through the chimney. They leave the house through white PVC piping.
Since the size of the old chimney flue was determined by the size of the furnace and water heater, the chimney flue will now be too big for handling the just the water heater gases.
This condition is often referred to as an Orphan Water Heater.
In northern climates such as Wisconsin, the negative effects can pose a health/ safety concern.
One of the byproducts of combustion is a vapor gas.
Since the chimney is now oversized for the water heater, there will not be enough heat to allow a proper draft to get rid of the gases. The flue gases condense on the inside of the clay chimney flue (if the chimney has a clay flue), and when the temperatures drop, spalling occurs.
What is SPALLING?
When moisture is absorbed into the porous clay, brick, block or mortar, and the temperatures drop, the moisture freezes, expands and forces chips to flake off of the surface.
With enough spalling, gaps are created which can allow dangerous flue gases such as Carbon Monoxide to find a path into the home.
The verbiage I use in my home inspection reports is:
Orphan water heater – A high efficiency furnace has been installed without installing a flue liner in the chimney for the natural draft water heater. Due to the removal of the natural draft furnace vent from the chimney to accommodate the high efficiency furnace conversion, the increased condensation will damage the interior of the chimney and create unwanted paths for dangerous flue gases such as Carbon Monoxide.
The current condition is a violation of WI Administrative Code SPS 323.11 (3) and the National Fuel Gas Code NFPA 54. For Health and Safety, contact a qualified specialist to discuss and implement a safety compliant alternative.
Installation of a power vented water heater is an acceptable alternative to the present condition. Contact a licensed plumber for remedial options and cost estimate