Orphaned Water Heaters

February 5, 2019
William Hussel

From about 1900-1980, many homes were built with masonry chimneys and clay tile liners. A skilled mason built the chimney to carry products of gas or oil combustion out of the living space to a point above the roof. These masonry chimneys depended on the fact that heated air rises, taking with it the products of combustion, which were pushed out into the atmosphere.

This type of chimney worked well back then, when oil and natural gas furnaces and boilers operated at about 60% efficiency; that is, 60% of the fuel energy wentinto heating the home and the remaining 40% literally went up the chimney. That was a good arrangement when fuel was cheap and chimneys needed to be kept warm for proper draft. Masonry chimneys were warm and happy, and the temperature inside the flue and vent connectors stayed well above the dew point of the products of combustion.

Efficient Furnaces Changed the Equation
As homes became more efficient and furnaces and boilers are vented directly to the outside without the need for the masonry chimney, things have changed. Deprived of the heat produced by a furnace, the clay-tile chimney turns cool.The “orphaned” water heater just doesn’t send enough heat up the chimney. When the temperature of the liner tile dips below the dew point of the water heater’s products of combustion, moisture condenses on the tile, masonry and mortar. Leaks can occur. Wet masonry chimneys alternately freeze and thaw, and eventually they fall apart. Outside chimneys and cold climates compound the problem.

Fixing the Chimney
A stainless steel liner inserted inside the tile and attached water heater flue will fix the problem. When the water heater operates in the winter, the small metal liner heats quickly and there is no condensation. Similar liners are also needed to prevent condensation on chimneys serving 85% furnaces and boilers.