The two parts that quietly kill your furnace & AC: the evaporator coil and heat exchanger
Two of the most important parts of your system are ones you never see — and when they get dirty, your bills climb, your comfort drops, and your equipment wears out years early. Here's what every Salt Lake Valley homeowner should know.
Your evaporator coil: where your cool air actually comes from
The evaporator coil sits inside your furnace or air handler, right above the blower. Your AC's refrigerant runs through it, and the warm air from your home blows across it — that's the moment your air actually gets cooled. Because every bit of air in your house passes over that coil, it slowly collects dust, pet hair, and the fine grit that Utah's dry air and summer inversions are famous for.
As that film builds up, three things happen:
- Airflow drops. A dirty coil is like breathing through a scarf — your blower has to work harder to push air through it.
- Cooling gets weaker. The grime insulates the coil, so it can't pull heat out of your air. Rooms stay warm even though the system runs nonstop.
- The coil can freeze. Restricted airflow can drop the coil below freezing and ice it over — now you get no cooling, water when it melts, and a compressor under serious strain.
A filthy or frozen coil also raises the pressure your compressor — the single most expensive part of your AC — has to fight. We've seen good compressors die years early simply because nobody ever cleaned the coil.
The secondary heat exchanger: small problem, big (and dangerous) consequences
If you have a 90%+ high-efficiency furnace, it has a secondary heat exchanger — extra passages that squeeze more heat out of the exhaust before it leaves your home. That's what makes the furnace so efficient, but it also runs cooler and wetter, so it's prone to a sticky mix of condensate, soot, and corrosion over the years.
When a secondary heat exchanger clogs or corrodes:
- The furnace can't move heat efficiently, so your gas bill creeps up.
- The system can overheat and trip its safety limits — short-cycling on and off, never really warming the house.
- If it cracks or badly corrodes, combustion gases (including carbon monoxide) can leak into your air. This part is literally a safety device, which is why we inspect it closely on every tune-up.
Why Utah homes are especially hard on these parts
Our valley runs your system hard in both directions — brutal July heat and deep January cold — and the dust and winter inversions load up coils and filters faster than a milder climate would. Hard water and dry air don't help. That's why a system that feels "fine" can be silently losing efficiency every season.
What you can do
A few things are DIY-friendly: change your filter on schedule (a clean filter is the cheapest protection your coil has), keep the outdoor unit clear of cottonwood, grass clippings, and debris, and gently rinse the outdoor coil fins with a hose.
The evaporator coil and heat exchanger, though, live inside the sealed cabinet and around the burners — cleaning them properly takes the right tools, coil-safe cleaners, and a careful eye for cracks and corrosion. That's part of what we check and clean on a maintenance visit, along with a close look at that heat exchanger for your family's safety.
Not sure when yours was last cleaned?
Book a tune-up and we'll clean, inspect, and test it — and tell you honestly what (if anything) needs attention.