There are all kinds of different companies offering furnace and air duct cleaning services these days. The gas company (centerpoint energy), the retail store (Sears), the plumber, the carpet cleaner, and probably your local handyman. If you try to find one on the internet, you will probably come across what I like to call lead aggregators, like "Service Magic" or "1800Contractor". Companies like these just sell the leads to third party companies that are usually really hard up for work, or new to the business. You will also probably run across a company that has several different domain names and website addresses, but the sure fire giveaway is the same phone number for each one.
Just Google the phone number and you will see all the other domain names pop up in the search. Then you have the companies that do the pay-per-click advertising. Rarely do you find these companies show up in the organic search results for any given relevant keyword phrase, such as "furnace cleaning mn" or "air duct cleaning mpls." Again, these are probably your fly by night companies that are new to the business or have really bad reputations and therefore can not get ranked organic on the web. My advice on this would be to pick the top 3 organic search results for your given search term, and make sure you got 3 different phone numbers, and no 1-800 numbers (unless you really enjoy a run-around.)
Now that you have found your 3 companies, the first question you will probably ask these companies is, "How much do you charge." This is where the real confusion sets in. Some companies proudly tout their $ 99 duct cleaning special (only read the fine print, or find out exactly what it includes.) Usually companies like these are scams. It is using the same old tactic we have all heard before, "bait and switch." You see, they will forget to tell you "for the first 5 rooms, each additional room costs $ 20" or "furnace cleaning extra" or "air conditioning coil cleaning $ 79" and my favorite "air exchanger compartment only $ 55 with duct cleaning."
The air conditioning coils, air exchanger compartment and the furnace itself, are a must, when cleaning your air ducts, and only takes the cleaner an extra minute or two to clean. My advice here would be to go with a company that includes the air conditioning coils, air exchanger compartment and the furnace for one flat fee (usually this only applies to homes with one furnace, additional furnaces usually means you have a rather large house, or the crew has to set up the equipment twice).
Ok, so you found a good local company at a good price right? Wrong. Did you ask what type of cleaning method they use? Well, I have heard of at least 4 cleaning methods, but I will just mention the 2 most popular. The first one is your "basic" or "air-sweep" method. This is where the cleaner goes to each register in the home with what is called and air wand, and blows compressed air down the branch lines into the main trunk lines. Then uses whats called an "air snake" that has a reverse nozzle which pulls all the dust and debris towards the furnace where the vacuum hose is set up.
The other method is the "roto-brush" method. This is where they take off all the regulators in the home and send a brush that is air powered, and goes in circles, knocking off the debris from the air ducts. In my opinion the basic method is just fine if you clean your furnace on a regular basis. Prices are typically in the $ 175- $ 225 ranger for this type of cleaning. If you just purchased an older home, and it does not appear to have been done in ages, you may want to go with the roto-brush method. Keep in mind, the roto-brush method is very time consuming and usually cost 3-5 times what a basic cleaning would cost.