Furnace Condensate Drains

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Like it or not, energy conservation is a part of modern lives and with space heating (and cooling) being one of the leading uses of energy in our modern world, furnace and boiler manufactures have had to radically change the design of their equipment to increase efficiency.

Simple Heater Efficiency Model

The simplest way to look at your home heating efficiency is to look at the amount of energy consumed (burned) by the heating unit and the amount of useful heat generated. In a 30 year old furnace, this may only be a 70% efficiency rating (i.e. 70-cents of every dollar of energy goes to heat the home). So where does the remaining 30% of energy go? Quite literally, it goes up the chimney as wasted heat. If more of the lost heat energy can be captured and transferred to the home, the efficiency of the furnace goes up.

How is Energy Efficiency Improved?

Furnace and boiler manufactures have employed many different changes from equipment design to materials used but the biggest increases in efficiency have come from 3 main areas:

  1. Electronic Ignition - Burning a constant pilot light wastes fuel. Electronic ignitions only light fuel in the furnace when heat is called for by the thermostat.
  2. Plugging the Chimney - Because warm air naturally rises, the warm air in the home will rise out of a conventional furnace chimney wasting energy. Newer furnaces effectively plug the chimney when not in use to prevent warm household air from escaping.
  3. Latent Heat of Vaporization - This concept takes us back to some high-school physics but basically when natural gas burns, a by product of combustion is water. In older furnaces, this water turns to steam and leaves the home out the chimney. By recapturing this steam and converting it back to water, the physics of this process generate additional heat which can be transferred to the home.

What is 'Condensate'?

In high efficiency heating systems, steam has been turned to water and the latent heat is used to heat the home. Condensate is the water that has now collected at the furnace and in some homes, managing this water can be a problem.

Typical condensate pump used when a no nearby floor drains are available.

The obvious problem with this condensate is a need to drain it away. If you have a floor drain nearby the furnace (or boiler), this could be as simple as a drain pipe flowing away with gravity. However, many homes were never built with drains at the basement floor level and in some cases the main sewer home drain is above the level of the furnace. In these cases, a 'condensate drain' may need to be employed. These essentially are mini-sump pumps that collect condensate from the furnace and when the level is high enough they pump water to a higher point in the home (like an upstairs sink) where it can drain away.

The non-obvious problem with condensate is that this water mixes with trace amounts of chemicals also found in the furnace chimney like sulphur and create a weak mixture of acids like sulphuric acid. Some municipalities require that the acid be neutralized before it can go down the drain which creates some extra maintenance burdens on the home owner.

Final Thoughts

As a home inspector, I've seen many furnaces where the condensate drainage system is not working correctly which results in water leaks in the furnace and damage to the cabinet and furnace systems, potentially causing premature failure of the furnace. If you have a condensate pump, check on it every time you change the furnace filter to be sure it is operating correctly.

By James Bell - Owner/Chief Inspector of Solid State Inspections Inc.