Readers wrote to me with questions about purifying the air in your home. These are the last things you can do to improve your indoor air quality.

“I’ve heard of a HEPA filter for air conditioning. What’s this? Should I buy one?”

HEPA stands for High-Efficiency Particulate Air. A HEPA filter works with a powerful fan to force air through a thick pleated mesh that traps pollen, pet dander, dust mites, and smoke. It can filter out almost all toxic microorganisms, including bacteria, mold spores, and viruses. Hospitals are one of the largest users of HEPA air filters.

Sounds great right? Let’s run to the store and buy one. Wait, not so fast. There are a couple of problems you will run into if you try to fit a HEPA filter into your air handler or return air ducts. The first is the expense: $ 10 for a vacuum-sized filter and more than $ 200 for commercial air handlers. The second problem is that residential air handlers don’t have fans with enough power to push air through HEPA-type media.

But there’s some good news: Since the whole point of using a fancy filter is to clean the air, there are things you can do to improve indoor air quality. One is to use a HEPA filter on your vacuum if it is a model that is designed to use HEPA filtration. The other thing you can do is buy a standalone air purifier, which I’ll talk about in a future article.

Without switching to a dedicated air purifier, the following things will help keep your indoor air fresh and clean.

A well-maintained vacuum cleaner with a HEPA filter used several times a week on floors and carpets will go a long way in keeping the air in your home clean. A non-HEPA vacuum with dirty filters, on the other hand, will actually add dirt and pollutants to the air by lifting it off the floor and redistributing it into the air.

Change your heating and air conditioning filters on a schedule and use high-efficiency air filters. The medium to high efficiency air conditioning filters sold in the supermarket are very good at catching unpleasant particles.

Minimize the use of candles and wood fires if you can. These add to the internal pollutant load.

Limit the use of strong air fresheners and cleaning products.

Do not smoke inside.

Use exhaust fans if you have them when you’re cooking, but don’t use them if you have a wood fire in your fireplace. The fan can draw smoke from the fireplace into the living room.

You can also call an air conditioning contractor to come over to your home and quote your air handling fan upgrade to one that will handle a HEPA installation. This is not an inexpensive upgrade, so you may want to try the above methods first, and then consider a standalone air purifier.

Opening your windows on nice days will go a long way toward cleaning the indoor air. Since the Environmental Protection Agency states that indoor air is two to five times more polluted than outdoor air, letting the breeze wash out pollutants will cut down on your to-do list.