Duct insulation can be a do it yourself project that pays you huge dividends. It will not only pay you back your costs but will pay you year in and year out for the rest of the time in your home. As energy prices rise, the amount you save will continue to grow. If your hvac ducts are made of metal and are located in an unconditioned area they could be costing you. These ducts typically lose 10-30% of every dollar you spend on heating and cooling. Do you have rooms where, during the heating season, it seems like the air coming out of the register is cold? A common name for that is "cold blow" and it can be caused by uninsulated ducts. That is a common complaint on heat pump systems. The answer is usually to insulate the ducts.
The following chart shows you the recommended insulation (R values) based on the climate conditions and duct location. Choose the climate that best describes your location and choose the location of your hvac ducts to find the recommended R VALUE.
If you insulate your metal ducts prior to replacing your hvac equipment, you may be able to purchase smaller units. you will generally pay less for a smaller unit. You can perform the duct insulation for a lot less than the cost of replacing the ducts.
Prior to insulating, you need to seal the ducts. This can be achieved with metal foil tape or duct mastic. DO NOT USE DUCT TAPE, it will not last. When using the foil tape, the ducts must be free of dust and dirt or the tape will not stick. The mastic comes in a gallon bucket and can be applied with a small stiff paint brush. It can also come in tubes and be applied with a caulking gun. Cover all the duct joints, takeoffs, and connections as well as any small holes you find. This will not only save you energy dollars. By sealing the return air ducts, you can stop the hvac system from drawing in pollutants from the unconditioned areas. This can improve the home's overall indoor air quality.
You can buy duct insulation in two different types. The first is regular fiberglass insulation combined with a foil backing. It also comes as a sheet of polyethylene bubbles sandwiched between two radiant barriers. This is sometimes called reflective insulation. Each type has an R value. This is a measure of the materials ability to resist heat flow. Typical values for this are from R4-R11. The higher the R value the better but the price also goes up. Usually it is only cost effective to install R4 to R8 depending on your climate. This usually comes in rolls with varying widths. Choose the widest roll that you will be able to work with for your conditions. It is easy to install. Just wrap the ducts and ensure a two inch lap at the seams. You want the seams to be on the top of the ducts. Then, you can staple the seam together and seal the seams with foil tape. Do this on round pipes as well as square duct. Cut as necessary and cover all boots and takeoffs as well.