How heating and cooling work in a manufactured home

The system in a manufactured home is laid out differently from a site-built house. Here are the parts, and what goes wrong with each.

The parts of the system

1 · Downflow furnace
Usually in a hall closet, blowing warm air down into the ducts under the floor. Replacement furnaces need to be listed for use in manufactured homes; a standard site-built furnace generally is not an allowed swap.
2 · Trunk ducts
One main duct runs the length of each section, inside the belly. Leaks and loose joints here send heated or cooled air under the house.
3 · Crossover duct
A flexible duct under the home joins the two halves of a double-wide. If it is crushed, torn or disconnected, the far side of the home gets weak airflow.
4 · Floor registers
Air comes up through the floor. Rugs and furniture over registers, or dust and debris inside them, cut airflow to the room.
5 · Outdoor unit
An air conditioner or heat pump beside the home, piped to a coil at the furnace; some homes use a packaged unit instead. Desert dust clogs its coil fast.
6 · Belly wrap
The underbelly board holds insulation and ducts in place. Tears let in cold air, dust and rodents — and let ducts sag.