ROC-NH staff

Tighten your belly, and keep heat indoors

By ROC-NH staff

To keep your manufactured home warm in winter, fix the home's belly and ducts.

What we learned from weatherizing hundreds of manufactured homes two years ago is that if we could make only one recommendation to homeowners, it would be to fix the home’s belly and ducts.

To understand why, you need to know how your furnace works.


A torn and sagging belly makes a good home for rodents, but an inefficient heating system.

In essence, the furnace re-heats the air in your home. When the air’s temperature in the house hits approximately 70 degrees, it is sucked into the furnace and heated to about 130 degrees. That warmer air is then pushed by a fan through the duct work under your floor and into your home through vents in your floor.

Keep warm air inside

Your goal is to keep warm air from escaping the ducts, and your home.

The first step is to be sure the vertical ductwork, called trunk line risers, that connect to your vents are sealed and properly attached both to your floor and to the main duct line (or trunk line) to prevent hot air leakage.

Then, be sure your home’s belly needs to be secure, with no rips or holes. The belly is usually a fabric stretched across and under your entire floor. The belly encloses your heat ducts, holds up the insulation and serves as a rodent barrier. This cavity between the fabric and the underside of your floor is very rarely well insulated and should be blown full of fiberglass.

Tight cavity insulates ducts

A tight, well-insulated cavity seals and insulates the ducts, which will then deliver an ample supply of heat to each end of the home. There are ways to test the belly’s tightness to make sure it is performing as well as possible, but they require the tools of an energy auditor.

The most important thing to know about insulation is that unless it is in full contact with the surface it is meant to insulate, it loses most of its ability to work. Most bellies contain fiberglass batt insulation that hangs six to 12 inches below the floor and is simply not effective.

If you don’t feel a strong flow of hot air at each end of the home, you probably have significant hot air leakage in your heating ducts. The squirrels like it, but it is expensive way to heat your home.

By the ROC-NH staff of the NH Community Loan Fund.

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