A forced-air heating system includes a heat source (usually a furnace or heat pump), a fan, and a duct distribution system with openings serving every room. It also needs a duct to return air to the heat source for reheating. A forced-air system requires considerably more space than most other heating systems.

The fan forces air through ducts and out through supply grilles. Registers are grilles with dampers that can be closed to reduce the flow of warm air. After the warmed air disperses and cools, it must be returned to the heat source, which requires separate return air ductwork and usually one or two large return grilles.

Where winter heating is more demanding than summer cooling, supply registers are usually located in the floor, because warm air rises naturally. The supply ductwork is thus often contained in a crawl space or basement.

Forced-air systems have several advantages over radiant or room-by-room systems. The fan and the duct system distribute heat throughout the house, minimizing cold spots. Water vapor from cooking, bathing, and perspiration can be dispersed. And air filtration can be added to the system (the filters that come with most forced-air systems are primarily to protect the heating unit from large particles).

For your heat source, consider whether a furnace or a heat pump better meets your needs. Furnaces supply only heat, while heat pumps provide cooled air in summer as well as warmed air in winter. Furnaces are usually fired by either natural gas or propane. Electric furnaces are available but should be avoided; the far more energy-efficient heat pump is a better choice if gas is unavailable.


Gas, propane, or oil furnaces require an exhaust flue, and should have a duct to supply combustion air directly from the outdoors. While it’s thermally advantageous to place the furnace within the house’s heated space, this is sometimes prohibited by the building code. Look for a furnace that utilizes sealed combustion; these draw combustion air directly from outside and expel combustion products directly outside.

Ask your contractor for high-efficiency equipment. A condensing furnace with about 95% AFUE (annual fuel utilization efficiency) is top-drawer; it recaptures some of the heat wasted in traditional systems by condensing water vapor from the combustion gases before they go up the chimney. As a result, it needs a small pipe to a floor drain or to the outdoors. The exhaust flue temperature of condensing furnaces is so low that plastic pipe flues are allowed; these can be vented directly outside, even near ground level.

The filter at the furnace should be cleaned or replaced regularly, preferably monthly. Forced-air systems can be expensive to maintain if you don’t keep up with routine preventive maintenance.

Heat Pumps

A heat pump works like an A/C in reverse; it extracts heat from the air, earth, or water outside your home to warm your house. Even in winter, there is always some heat to be extracted. A heat pump’s efficiency is given as HSPF (heating seasonal performance factor) or COP (coefficient of performance). The higher the number, the greater the efficiency; aim for an HSPF of 9 or higher. The most common complaint about heat pumps is that they need periodic maintenance.

There are two types of heat pump: air source and ground source (also known as geothermal or water source). Air source heat pumps are far more common. They consist of an outdoor unit that extracts heat from winter air and an indoor unit that delivers the heat.

A ground source heat pump has an extensive underground pipe loop through which fluid circulates to pick up heat from the earth. That heat is then extracted from the fluid and delivered into the home. The underground loop is laid out either in horizontal trenches or in a series of vertical wells, making the system prohibitively expensive for many homeowners. Ground source systems are often plagued by installation and sizing errors, and their rated performance does not include the energy required for ground loop pumping, making them appear to be more efficient than they are.

Air source systems are far less expensive to install, but the outdoor unit can be noisy, so be careful where you locate it. Newer high-end heat pumps are much quieter; ask your contractor for the sone rating on the pump you’re considering. A heat pump must work harder to glean heat from very cold air than from the ground, so expect lower efficiency from an air source system. Where winters are very cold, a ground source heat pump may be a better choice.

If you live in a very cold climate, you will need a backup heat source. One common choice is electric-resistance coils integrated with the system, but these can cause electricity consumption to skyrocket in really cold weather. A more energy-efficient option is an inline “gas pack” or “dual-fuel” system, which adds a gas coil to the duct system. Consult your HVAC pro to determine the best system for your home and climate.

The ductless mini-split is another type of heat pump that can be appropriate for an addition or a whole house; it is discussed later under room-by-room systems.


Ductwork must be both sealed and insulated. Make sure there’s enough space for duct insulation and for accessing your ducts to check on the condition of insulation and duct sealing. If you can incorporate the ductwork within the heated space (for example, in a dropped hallway ceiling or by insulating at the roof rather than the attic floor), you can get away with using less insulation.

Ducts gather dust and debris over time, so they should be cleaned by professionals every few years. This is especially true for return ducts in the floor.

Views: 537

Replies to This Discussion

Hi everyone! I'm new here & hope I can benefit from members' know-how. Last Summer I moved into a new double-wide ( modular ) home in a nice trailer park in Cold Spring, NY - I've been amazed by the exorbitant propane heating bills - I've recently bought a woodstove that I plan to hook up soon. That should impact my propane bills significantly ( I'm hoping!), and I'm wondering if I should disconnect the propane from the heating unit. It's a forced-air/duct system that is quite convenient and works well, despite the cost.
I also have a 'dummy' question : how can I tell what is and isn't hooked up to the propane tanks?

Thanks in advance !


© 2020   Created by Home Energy Saver.   Powered by

Badges  |  Report an Issue  |  Terms of Service