Re: Air Cleaner Short-cutting and Room Size

A Reader writes:

Ed,

I cannot thank you enough for your thoughtful analysis of my situation.

I agree with your reasoning that the IQAir should be placed in the bedrooms so based on your recommendation I am going to buy an IQAir for each bedroom and a single Austin HealthMate for the kitchen/living room.

The 15 pounds of carbon in the Austin should help absorb kitchen smells and the noise will be a lesser issue on that side of the house.

My only follow up question about the Austin is about bypassing/short-cutting.

Based on what I have read the air intake occurs along all four sides and exits near the top.

Is this enough separation so that the unit cleans the air in the whole room and not just around the machine?

Thank you again for your extreme helpfulness in assisting me.

Ed's Reply

Hey Reader;

There is no air purifier that cleans the far reaches as effectively as the air near the machine.

If you look at dust with incoming sunlight or a strobe light, you'll see visible sized dust moving swiftly into the machine.

But dust further away is moving slower, and in the corners of the room barely at all.

This does not mean that the entire room is not eventually cleaned, but is a main reason for my room size recommendations being lower than the industry norm.

Rating an air purifier for room size by dividing room volume by air output (on high) to yield air changes per hour (ACH) is misleading. In addition, HVAC fan strength and frequency, sources/traffic in the room, dividers and furniture, and infiltration rates make every room different.

I advocate periodic dust ups - running a fan in the room with the air cleaner on high - along with aggressive vacuuming, to get far reaches of the room clean.

But airborne fine particles will always remain at a background level, and pick up whenever the purifier is off.

The Austin's design is as good as any in this respect. There were some downdraft machines (Honeywells) a few years back that blew air along the floor, but these were discontinued in favor of updrafts.

Short-cutting is worst on low speeds, which lack entrainment velocity for larger sized particulate, in an inverse square relationship with distance.

See

IQAir laser tests under the headlines "Tests of IQAir Efficiency," and "Let's Test HealthPro Ourselves," for a description of particle counter testing.

I used a particle counter at a constant distance from the air cleaner, about six feet. Note that it took over 6 hours of high speed operation to lower readings to minimums at that distance.

Particulate declined even in adjacent rooms in my home, but was always lowest near the machine.

I always recommend ventilation, source removal, and over-installation of air cleaners.

Best wishes,

Ed