Air inside home is often more polluted than outside the house

Friday, October 23rd, 2009

The denser the furnace filter the smaller the particle it will clean from circulating air


Mike Holmes checks out a customer’s furnace an essential part of improving home air quality.

Every furnace has a filter installed at the cold air return duct that filters the air returning to the furnace from the house.

Would you believe the air inside your home is more polluted than the air outside — in some cases 100 times dirtier?

And that new homes usually have poorer indoor air quality than older homes?

Newer homes are designed and built tighter to increase energy efficiency and reduce air leakage.

That’s great in terms of saving money, but we also trap everything in the air, like the VOCs (Volatile Organic Compounds) that off-gas from furniture and building materials, mould, allergens, pet dander and dust mites and the residual odours from cooking and pets.

And that bad air can lead to allergic reactions and health concerns.

We need to make sure the air in our homes is as clean as it can be — and that means removing as many pollutants, such as particles and gases, as we can.

Particles are made up from dust, pollen, pet dander, soot from smoke, dust mites and mould spores.

Gases come from VOCs and from the combustion of stoves, fireplaces and furnaces.

Every furnace has a filter installed at the cold air return duct that filters the air returning to the furnace from the house.

This does remove some pollutants from your home, but it’s really designed more to protect the furnace from dust and dirt buildup on the heating coils and fan motors.

It will also help clean your indoor air to some extent — usually collecting larger particles.

The design and density of your furnace filter will determine how many, and what size, of the particles it will collect.

The denser the filter, the smaller the particle it will capture.

Air filters need to be changed frequently, or they can’t do their job.

It is very important to make sure you only use the filter that is designed for your HVAC system.

Many residential HVAC systems don’t have enough fan capacity to accommodate high efficiency filters and you may restrict air flow and affect your furnace’s efficiency.

A much more effective way to clean your indoor air is to install a HEPA ( High Efficiency Particulate Arrestance) filter.

HEPA filters also trap particulates, just like your furnace filter, but they will capture particles of a much smaller size.

HEPA filters alone remove 99.7 per cent of particles in the air, but they don’t trap gaseous pollutants like VOCs.

But, you can’t just put a HEPA filter into your mid-efficiency furnace, as a replacement for your standard foam or pleated furnace filter.

True HEPA filters are typically installed only in homes with HVAC systems designed to accommodate the airflow they require.

You can buy free-standing HEPA units that are used separately from your HVAC system, and make sure you have one on your vacuum cleaner.

Cleaning VOCs, gases and odours from your air requires an activated carbon filter.

These absorb airborne chemicals and gases, but not particles.

Carbon filters are designed for specific gas pollutants so they don’t get everything in the air, just those they are designed for.

No filter gets every gas. Carbon monoxide is one gas that will not be captured by any indoor air cleaner — you need a carbon monoxide detector and alarm for safety.

Depending on your home and the kind of pollutants you produce, the lifetime of your activated carbon filter can vary.

The filter medium gets saturated and needs to be replaced promptly, or the filter won’t be able to do its job.

That’s why you’ve got to do your job, and make sure you change the filter.

Another air-cleaning technology uses ultraviolet light to kill bacteria, mould and viruses.

UVC irradiates and breaks down micro-organisms by disrupting their molecular bonds, making them unable to reproduce and ineffective — that way it “kills” or neutralizes them.

UVC is very effective at sterilizing air; it’s been used in hospitals for years.

It also needs to be used with a particle filter, like HEPA, because even a dead mould spore can cause an allergic reaction.

UVC lights are installed inside the ductwork or your HVAC system.

Since they are light bulbs they are going to accumulate a coating of dust over time so they’ll need to be replaced periodically.

The bulb will also lose intensity over time, and you’ll need to replace it according to the manufacturer’s directions.

The effectiveness of the UV light depends on how intense it is — some systems coat the interior of the duct around the bulb with mirror to increase the intensity — and on the wattage of the bulb.

How long the micro-organisms in the air are exposed to the light is also important.

So, if your airflow is very fast, the exposure time will be shortened, and the effectiveness reduced.

Catch Mike in his brand new series, Holmes Inspection airing Thursdays at 8 p.m. ET/PT on HGTV. For more information visit


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