How to clean re-heat coils located within high efficiency furnaces. Why is it important?

Air duct and furnace cleaning professionals will be seeing a lot more high efficiency systems in the coming years. Gone are the days of simply removing a blower and cleaning the system. All high efficiency furnaces are equipped with a primary heat exchanger as well as a secondary heat exchanger. These systems are designed to take advantage of the exhaust created from the primary heat exchanger to heat a secondary heat exchanger which reduces fuel burn. Secondary heat exchangers can come in the form of coils or a metal tubing like apparatus. For the purposes of this article I will refer to the secondary heat exchanger as a “reheat coil”.

The secondary heat exchanger or “reheat coil” is almost always located directly above the blower making them prone to collecting more dust and debris than air conditioning coils. This is why it is imperative to access, inspect and clean these coils in order to properly clean the system. The process does take patience as removing the blower can be more complicated than working on a basic furnace. It will require removing hoses, wires and other parts in order to freely unbolt the blower from its mounts. Take your time and make sure to make reference of how everything goes back into place by either writing down a schematic and/or taking pictures.

Most build up will be on the blower side or bottom of the reheat coil. Place your vacuum suction below the reheat coil and using air pressure carefully blow the coil clean. Beware the fins of the coil are easily bent so keep your air pressure a few inches away from the coil surface. Try not to blow air directly up through the coil as sometimes the top of the coil is inaccessible due to the presence of air conditioning coils that have been installed directly on top of the furnace which leaves no space for an access hole. To avoid this, use your air pressure at an angle to blow as much dust and debris towards your vacuum suction. If it is possible to cut an access hole on the main plenum directly above the furnace, leave your vacuum suction below the reheat coil and clean the topside of the coil using the same technique with your air pressure. In extreme cases the use of a chemical coil cleaner may be necessary as a final step.

Thanks for reading and I hope you will find this article helpful in the future.

Also, feel free to take a look at our Duct Cleaning Training video below (removing the blower). The video doesn’t cover everything in this article, but it may be a helpful reference.