About a year ago at my home in Northern Michigan, it was noticeably chilly inside and around 35°F outside. The two single-zone, cold-climate minisplit systems should have had no problem maintaining the 70°F setpoint. I turned the systems off, popped open the covers, and sure enough the filters were caked with dust—it’d been a while since I last checked them. I removed the filters, cleaned them with a handheld vacuum, and reinstalled them. The system was back to normal.

Then, a few months ago, a friend shared an article about the annual maintenance costs of a minisplit system diminishing the savings after switching from natural gas. It’s difficult not to digress with counter arguments, but let’s focus on the annual maintenance. I learned that one important step includes a deep cleaning of the indoor unit, which was something I hadn’t done.

Then, I got to thinking about when I’ve helped troubleshoot minisplit systems. One of the first questions to ask is when the filter was last cleaned or changed. Responses have ranged from “regularly,” to “oh yeah, it’s been a while,” to “what filter?”.

Given a typical homeowner’s lack of awareness about the importance of filter maintenance and indoor coil cleaning, I figured it’s a good opportunity to share my experiences. I’ll start with basic operation and identify some components to better understand the importance of maintaining the systems. Then, I’ll move on to the procedures.

Rundown of the basics

Minisplit systems have at least two coils that are fin-tube heat exchangers, one for each indoor and outdoor unit. True to their name, they are made of a tube with multiple bends that has several fins welded to it. The fins are spaced roughly a millimeter apart, about the…