Question: How do heat-recovery systems work?

Answer: Kitchens use a lot of heat, and, unfortunately, much of that is wasted—through exhaust hoods, down the drain and into the kitchen itself.

Fortunately, you can install a heat recovery system that can help you recapture that heat and use it to reduce both your waste and your overall energy use. Heat from exhaust hoods, hot dish water and refrigeration can be used to pre-heat makeup air or domestic hot water, which reduces the load on your energy systems and reduces your costs.

How does it work?

At a basic level, make-up air or domestic hot water passes through a heat exchanger and is heated with the energy that’s been captured from an appliance like a dishwasher, walk-in freezer, or exhaust hood. Although the water or air that’s heated this way may not be quite warm enough to use at that point, pre-heating air and water allows your furnace or hot water heater to work less.

Common types of heat recovery systems include:

  • Kitchen and dishwasher hood recovery systems to pre-heat makeup air (although using kitchen hood heat can be challenging due to grease build-up on filters and heat-exchanger surfaces)
  • Dishwasher and sink hot water used to heat hot water
  • Hot air in the kitchen used by a heat pump to preheat hot water
  • Heat from refrigeration units used to preheat makeup air or hot water

Do these systems really work? And, more importantly, do they save money?

The new Cambridge Mill certainly thinks so. The newly-refurbished restaurant in Cambridge, Ontario, installed an energy-recovery ventilation system that captures 85 percent of the heat lost through the kitchen’s exhaust system and uses it to pre-heat both the building’s makeup air and domestic hot water. Among other benefits, the system, which has an estimated 3.5-year payback period, allows the hot water heaters to use less energy, as they’re heating water that’s already 95 degrees. (For complete details on the Cambridge Mill’s energy-efficient systems, take a look at our May, 2011 article.)

Do you have a heat recovery system in your kitchen? Has it saved you money? Share your experience in the comments section.