Furnace runs but house never reaches set temperature, long run times

Safety first: Turn off power and gas before opening burner compartment.

• Step 1 – Check filter and airflow: Ensure filter is clean and all registers are open to maximize airflow.
• Step 2 – Inspect burners: Remove burner access panel and visually inspect burners for rust, debris, or misaligned flames. Do not attempt major burner disassembly without training.
• Step 3 – Check ductwork: Inspect accessible ducts for disconnected joints, large leaks, or crushed sections. Seal with mastic or metal tape (not cloth duct tape).
• Step 4 – Professional evaluation: A technician should measure temperature rise, gas input, and compare furnace capacity to home load if undersizing is suspected.