[Optional but highly recommended]
HVAC professionals recommend changing furnace filters quarterly to extend a furnace's life. This can also serve as a quarterly inspection for your unit(s).
Labor is $25 for the first unit at a property plus $10 for each additional unit at the property.
Material is given at cost.
This is calculated using the following formula:
$25 + ((number of units at property -1) x $10) + materials