There are varying opinions on the type of cleaning to have done on your air ducts. My opinion is that it varies based on the type of duct work you have. If you have solid material (typically metal) ducting you can have use a company that uses a brush to scrape the system clean. If you have flexible plastic or foil ducts the solvent cleaners are generally a safer bet since the brushes often tear holes in the soft material and/or pull joints loose. It really depends on what type on ducting you have. You're ducts will collect all kinds of dirt, skin cells and allergens over time so if you see dicoloration around your vents it is probably time to get them checked and cleaned.
Also, don't stop at the duct work. Don't forget your annual system check up by a licensed HVAC technician. They'll make sure your system is running at peak performance, keeping it running efficiently and with as little impact as possible on your electric bill. You can often save the cost of the annual tune up in the electricity cost saved. If you have a natural gas system a bi-annual check and cleaning of the HVAC unit may be advisable to save electricity and gas.
Todd Shell
Todd's Home Services
www.thomeservices.com