Duct cleaning is one of the few home services where the customer usually cannot tell whether the work was done well. The ducts are hidden, the equipment is in an attic or a closet, and the before-and-after looks the same from the hallway.

These five questions sort out who is doing it properly. Ask them before you book, not after.

1. Are you NADCA certified, and who on the crew holds the certification?
NADCA is the National Air Duct Cleaners Association. It publishes the industry standard for this work and certifies individuals as Air Systems Cleaning Specialists by examination.

Ask who holds it, not just whether the company claims it. The credential belongs to a person, and a company can display a logo while sending a crew with nobody certified on it.

2. Are you a licensed HVAC contractor, and what is your license number?
Most of what goes wrong inside an air system is HVAC work. A loaded blower wheel has to be pulled and cleaned. A coil that can only be reached from one side has to be removed, which means handling refrigerant. A rusted secondary drain pan has to be replaced. Those require a license in Texas.

A cleaning-only company that finds one of them has to tell you to call someone else, or work around it quietly. A license number is a specific, verifiable fact. Ask for it.

3. Will you measure static pressure before and after?
Static pressure is the air pressure moving through your system, and it is the most useful single measurement on a residential system. It takes ten minutes and a drill bit.

It matters here because it is the one honest way to show whether the cleaning did anything. A reading before and a reading after is a number you can hold them to. Without it, you are taking their word for it.

4. How will you clean both sides of the coil?
The industry standard requires both sides of a coil to be cleaned. The dirt collects on the entering-air side, which on most systems faces down into the furnace where you cannot see it.

If the coil is butted up against the furnace, there is no way to reach that side without removing the coil or installing a service transition to create permanent access. A company that tells you they will clean it from the top is telling you they will clean the side that is not the problem.

5. What do you do if you find mold on fiberglass duct board?
This is the one that separates people, and most homes in this area have duct board plenums, so it comes up often.

The correct answer is that it has to be removed and replaced. Fiberglass is porous, so growth is in the material rather than on the surface. It cannot be vacuumed out, and no antimicrobial product is EPA-registered for use on porous surfaces inside an HVAC
system.

If the answer involves fogging, sanitizing, disinfecting or sealing it in with a coating, that is the wrong answer. No sanitizer, disinfectant or fungicide is EPA-registered for use inside residential ductwork at all.

One more thing worth knowing
A light film of dry dust inside a duct is normal and does not necessarily require cleaning. That is the industry standard's own position, and any company willing to tell you that is a company worth listening to.

Miller Climate Control is NADCA certified and a licensed Texas HVAC contractor,
TACLA24427C. Georgetown owned since day one.