Performed Fau maintenance on 6 year old Rheem system. Cycled system for heating. Verified proper heating sequence of operations. Temperature rise across heat exchanger is high but within range. Merv 11 filter is extremely clogged which can be why unit is operating a little hotter than usual. Checked and ensured all registers were open. Ran system through 20 point inspection checklist. Homeowner had no filters on hand and will be ordering and replacing himself. Went through findings and recommendations. Cycled system, system is operational upon departure.