Orphaned Hot Water Heaters
One of the most common items seen in home inspections are orphaned hot water heater. This primarily is the result of replaced furnaces (moving from a lower efficiency to high efficiency) and continuing to vent the hot water heater out the chimney.
Over the last few decades, furnaces more efficient. With greater efficiency in furnaces, more heat is kept in the home rather than being lost up the chimney. The conventional furnaces, kept about 60% of the heat in the home, with a loss of 40%. Mid efficiency furnaces kept more than 80% of the heat. High efficiency retained 90%.
Even though more heat is retained in the home, it has created some challenges and problems related to hot water heaters.
With high efficiency furnaces, the exhaust is cooled enough such that it can be vented horizontally using PVC pipe, out the side of the home. The chimney is no longer used for furnace venting exhaust.
Many times, when changing to a high efficiency furnace, the forgotten hot water heater is still vented through the chimney. This creates a situation called an orphaned hot water heater. A condition which needs to be corrected. This affects chimneys with non metallic flues. Let me explain.
For conventional and mid efficiency furnaces the exhaust pipe is vented below the hot water heater exhaust pipe into the chimney flue. During the colder part of the year, the heat from a conventional or mid efficiency furnace helps to raise exhaust pushing it out of the chimney. However, there may not be enough buoyancy to raise the warm air out of the chimney, against the cold air when only a hot water heater vents to the flue. Without the furnace’s additional warm air, the exhaust may be backflow, creating a carbon monoxide hazard. In addition, the hot water heater does not heat up the chimney flue. The hot water heater’s products of combustion will condense on the tile, masonry or mortar, if the temperature of the tile is below dew point. The chimney may deteriorate when leaks occur in the flue and moisture impacts the chimney’s masonry and mortar with the freeze and thaw cycle.
I suspect that the orphaned hot water heater issue may be the result of the tradesmen. Heat, Ventilation and Air Conditioning professionals install furnaces and air conditioners. They are not concerned about hot water heaters. That is the plumber’s job. So when they go to make money and sell a more efficient furnace, they do not want to add costs by mentioning an orphaned hot water heater. This would cost more money and they might lose their sale. Respectfully, I think they should represent the client and bring the orphaned hot water heater up.
Hope is not lost. Here are some solutions:
1. A metal liner may be installed in the chimney.
2. The hot water heater can be replaced with an electric hot water heater, no exhaust
3. A power vent hot water heater may be purchased. A vent pipe exhausts horizontally out
the side of the home.
When replacing furnaces, make sure that the HVAC technician follows specifications for exhausting material, sizing of pipes, and the flue’s size.