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We humans love our furry companions. And for some of us, let's face it, our perception of their cuteness directly correlates with their level of fluffiness (with exceptions, of course). Alas, our heating and cooling systems do not find their fluffiness so adorable. The monstrosity below was encountered by one of our technicians at a home in Plymouth, MN, when he created an access hole in their main return duct. At the risk of stating the obvious, the homeowners had a large dog, and it had been many years since their ducts had been cleaned.

Pet fur inside the air ducts

Those of us with pets know how ubiquitous their fur is—it's everywhere! As your pet moves around the home, loose hair becomes airborne and comes to rest on the carpet, on furniture, in your food(!), and in the vents. Since animal fur strands are generally much larger than run-of-the-mill household dust, they get hung up much more easily than smaller particles. Once hung up inside the ducts, they become a magnet for more fur and for other debris, creating mats of fur and dirt like the one pictured above. 

Pet fur also builds up much more quickly inside the ducts. Whereas typical household dust takes years to build up to an extent that it needs to be removed, animal fur, because of its size and the sheer volume of it, reaches critical mass sooner. Consequently, while people without pets can get by on a standard or "maintenance-level" air duct cleaning every two years, as recommended, those with pets may wish to have the higher level of service performed as their "maintenance" duct cleaning. 

Pet fur inside the furnace

Once pet fur is inside the vents, it moves through the ducts and, under normal circumstances, will be stopped from entering your furnace by the air filter. There on the filter it builds up and, unless the filter is changed regularly, it will become clogged with fur. With some frequency, our technicians have seen filters become so clogged that air cannot move through them, and the filter then bends and can even potentially be sucked into the furnace (and on at least one occasion, ripped apart by the blower wheel!).

Once the filter is clogged to this extent and bent, it is of course no longer functioning as a filter of any kind. At this point filter bypass comes into play, where debris simply goes right around the filter into the furnace. (Filter bypass can also occur when an air filter is ill-fitting, incorrectly installed, or extremely low-quality, such as cheap fiberglass, for example.)

The last place you want pet fur: the evaporator coil

It's inside the furnace and its various components that pet fur becomes extremely problematic, settling into the individual parts, clogging them up and reducing air flow. Since the entire heating and cooling system relies on good air flow to function optimally, efficiency can be greatly reduced when air flow is compromised by fluffy-furry debris.

The evaporator coil (A coil) is particularly susceptible to buildup, since all the air that circulates through your HVAC system passes through it. Both the furnace and the air conditioner will lose efficiency, work harder, and be subject to break-downs when air flow through the evaporator coil is compromised. The close-up above shows a mat of pet fur choking off air flow on the delicate fins of the coil. Because of the sheer size and "magnetic" quality of animal fur, if it manages to bypass the filter and reach the evaporator coil, it has the potential to disrupt the entire system

Above is what the evaporator coil should look like without its fur coat, the tiny holes free and clear of debris, allowing for easy movement of air and for the transfer of heat. If the coil above had a face, it'd surely have a smile on it.

Cleaning fur from the HVAC system

Considering the potential ravages of animal fur on the heating and cooling system, and that preventive maintenance is always a better (and less costly) option than repair, homeowners with pets should consider opting for the highest level of air duct cleaning service, including a furnace cleaning. Thereafter they should opt for at least the mid-level service as a maintenance cleaning. Why? Because for most companies, the top-tier service would include use of a tentacled air whip or brush used on the main trunk and the branch lines. The physical contact of the tool against the walls of the ducts—as opposed to the mere blowing that air pressure would provide—would aid in loosening any pet fur clinging to them. 

A thorough furnace cleaning would then remove from the inner components of the furnace any fur that made it past the filter—hopefully before it becomes too abundant and reaches the evaporator coil. 

So as a savvy homeowner and a diligent pet owner, in addition to frequently vacuuming your carpet to remove pet hair from all the places you can see it, consider having your air ducts cleaned frequently to remove it from all the places you can't

.Wanna dig deeper? Download our free tipsheet: 10 Questions to Ask Before Hiring an Air Duct Cleaning Company. 

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Many thanks to our technicians Ben S and Roy S for lending their expertise to this article.