Completed 1 system furnace repair and preventative maintenance check. Replaced the filter provided by the customer. Recommend installing a bigger return pedestal box. Return is too small and using a 12x12x1 filter. The system is designed for a 20x20x1. Recommended increasing size of heat strips. The customer said the system struggles to heat the house. Heatstrip now is a 5kw. Recommend an 8kw. Recommend getting the duct cleaned along with the system. Emailed all estimates to the customer.