Orphaned Water Heaters for Home Inspectors
by Joseph Meehan, Certified Professional Inspector®
What Is an Orphaned Water Heater?
An orphaned water heater is an atmospherically vented water heater that was previously vented together with another fuel-fired appliance which no longer shares the same flue.
Low-efficiency fuel-fired appliances that are in close proximity to each other are commonly vented together. To create the proper updraft in the flue, the flue is sized to accommodate the BTUs of the larger appliance.
But what happens when one of the appliances is replaced with a high-efficiency model that requires its own venting system? The smaller-BTU appliance is often left connected to the same flue in which its exhaust gases no longer contain enough heat for proper updraft.
How to Identify an Orphaned Water Heater
Look for a water heater that is connected to a metal flue with another larger, sealed-off connection below it. When fuel-fired appliances are vented together, the smaller appliance connects to the vent above the larger appliance’s connection. The larger connection will most commonly appear below the water heater’s connection.
In older homes, you may encounter an orphaned water heater that is connected to a masonry chimney. When the appliances were vented together, they created enough heat to create a proper draft in the large chimney flue, but the water heater alone cannot. In most cases, the flue of a masonry chimney is too large for a water heater alone to create a proper draft.
In both cases, look for signs of backdraft around the draft diverter. Scorched or melted material in this area is a sure sign that hot exhaust gas is escaping around the draft diverter and into the home.
The home inspector should also inspect the flue itself. Exhaust gases contain water vapor that condenses on flue walls without proper draft. Corrosion on metal flues and spalling or other damage at the base of masonry chimneys indicate condensation in the flue.
What Are the Implications of an Orphaned Water Heater?
Backdraft
Backdraft occurs when an appliance does not produce enough heat to create a proper draft. Heated gas that contains carbon monoxide spills out around the bottom of the flue and enters the home. This is a dangerous condition that should be corrected immediately.
Damage to the Flue
Water heater exhaust gas contains water vapor. Without proper draft, water vapor can condense on the flue’s interior walls. In a metal flue, this can cause corrosion and damage to the interior walls. In a masonry chimney with a clay flue liner, this can cause damage to the clay liner as well as the masonry itself. As condensation builds up, water seeps into the joints of the flue liner and into the masonry, where mortar deterioration, spalling, and other damage occurs.
What should be done about an orphaned water heater?
Install a properly sized flue.
An oversized metal vent flue can be replaced with a flue that is properly sized for the appliance according to manufacturer’s specifications and applicable codes.
Install a metal flue liner.
A metal flue liner is typically installed when a water heater is vented into a masonry chimney. The inspector should look for evidence that the chimney has been lined with a metal flue vent that is properly sized for the water heater. During the roof inspection, make note of any chimneys that have a metal flue with a rain cap extending from their opening. This is a good indication that a metal flue liner that is properly sized for the appliance was installed.
Install a different water heater.
Many orphaned water heaters will be approaching the end of their service life. Talk to your client about the situation, explain the implications, and let them know that the easiest and most cost-effective solution may be to purchase a new electric or high-efficiency water heater.
When to Defer to a Specialist
There are many variables that go into sizing a flue: height, BTUs, material, location, etc. It is beyond the scope of the home inspector’s job to determine if a flue is properly sized. In the case of an orphaned water heater, the inspector may assume that the flue is no longer properly sized and defer to a specialist for further evaluation. The exception to this rule is a water heater that is vented into a masonry chimney that has a metal flue liner installed.
Carbon monoxide poisoning is a serious danger to anyone living in the home. An orphaned water heater that shows signs of backdraft around the draft diverter should be corrected by a professional immediately. Furthermore, the inspector should notify any occupants of the home that a potentially dangerous condition exists.
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