Does it make sense to clean your HVAC ducts?
By Arnie Katz
Q: One of my neighbors told me about a local company that cleans the inside of the heating and air conditioning ducts. They said it makes the air in the house healthier and also saves energy. Is this really worth it?
A: There are two issues here, so we'll talk about each of them. First, I've never been able to find any research that shows energy savings from duct cleaning. There is some research that suggests cleaning the blower and the coil, and cleaning or replacing the filter can improve efficiency and save some energy. But duct cleaning? It seems very dubious, even though there are a lot of websites making the claim. These are, of course, mostly companies that sell duct cleaning services, but occasionally it shows up on utility sites as well. My advice? If anyone trying to sell you duct cleaning claims it will reduce your energy bills, calmly show them the door. They are either badly misinformed or dishonest. If the service includes cleaning all of the other components of the system, it may be worth considering.
The second issue is more complicated. Most people who choose to have their ducts cleaned do it for health reasons. They expect cleaner air in their home as a result. Here are a few things to think about:
If the ducts are dirty, how did they get that way? There are basically three ways this can happen:
- The registers and grilles were not covered during construction or remodeling, so sawdust, drywall dust, half-eaten Big Macs and other debris wound up in the ductwork. This is not uncommon.
- The ducts were not sealed properly. Many duct systems were sealed with tape, which does a poor job and tends to deteriorate over time. Sadly, some contractors still use tape instead of using duct mastic on the joints. If the ducts are leaky, then dirt, dust, critters and other contaminants can get in.
- If there is not a working filter on the system, dirt can get into the system during the normal course of living.
In some homes, all three of these can be identified. One of the problems with dust, dirt, dead camel crickets and mouse droppings getting into your ductwork is that another name for all those things is mold food. Organic matter plus a little moisture can lead to mold and other biological growth. This can be a real problem, especially for folks with asthma or allergies.
So the first thing to do is to make sure the ducts are sealed and the filter is working well. There is no point in spending money to clean the ducts if they'll just be contaminated again. And sealing the ducts is often a big energy saver.
If there is contamination in the ductwork — especially if someone in your family has respiratory problems — cleaning the ducts is worth considering, particularly if you have metal ducts that are not lined with insulation on the inside. These ducts can be cleaned effectively. Ducts with insulation on the inside are more difficult to clean well, and there's a risk of putting fiberglass into the air stream, which may be a health risk for some people.
Similarly, if you have flex ducts, it's more difficult to clean them well. Care must be taken to not tear up the inner liner, which would interfere with air flow and expose fiberglass to the air stream.
I've talked with folks who are convinced that cleaning the ducts improved their health. I have no reason to doubt them, although it's not clear if the other measures — sealing the ducts and cleaning the fan and coil and replacing the filter — were also done.
Bottom line? There is no evidence that duct cleaning by itself has any impact on either health or energy use. There is some evidence that a comprehensive cleaning of the system, in conjunction with sealing all holes, cracks and joints can have positive effects, but you can expect to pay a lot more for this service.
The most comprehensive study of this to date was done by the U.S. Environmental Protection Agency (EPA) in partnership with the National Air Duct Cleaners Association. It's available at http://epa.gov/iaq/pubs/airduct.html
Arnie Katz is director of training and senior building science consultant at Advanced Energy in Raleigh (www.advancedenergy.org). Send your home energy questions to firstname.lastname@example.org