Air flows through a furnace one of three ways: up, down or horizontally. A downflow furnace takes in cool air from the top, warms it, then releases the warm air at the bottom and pushes it through the ductwork below. Upflow furnaces, as you may have guessed, work the opposite way.
Downflow furnaces are usually installed in the attic, but sometimes they can be placed in the garage or main floor of the home. Generally, they’re less desirable than upflow furnaces because they are less efficient, but for some homes they are the only option.
Most upflow and downflow furnaces can also be used as horizontal furnaces by placing the unit on its side. However, a horizontal furnaces is really on necessary in very tight spaces such as small attics or crawl spaces. Other units are completely convertible, serving as upflow, downflow or horizontal units, depending on positioning.
The average downflow furnace costs about $2,000 to $3,500, including installation. The furnace itself usually costs $1,000 to $1,500, while labor adds an additional $1,000 to $2,000. Very high-efficiency models can cost $5,000 or more to buy and install.
Downflow furnaces are very similar in price to upflow furnaces; however, the installation could be more expensive in certain situations. If the furnace is going into a small attic, for example, plan to pay a bit extra.
- Works for all homes - A downflow furnace can be installed in any type of home. Unlike upflow furnaces, you don’t need a basement or crawl space.
- Not as efficient - Downflow furnaces are not as efficient as upflow furnaces because they’re fighting against the natural tendency of heat to rise.
- Harder to install - Downflow furnaces have stricter installation requirements. They cannot be installed directly on carpet, tile or any other combustible material, with the exception of wood. In many cases, you need to buy a separate subbase to create a barrier between the furnace and combustible flooring.
- Less comfortable heat - Most people find the heat produced by upflow furnaces more comfortable because they heat the feet first. Downflow furnaces heat the upper portion of the body first.
An upflow furnace takes in cool air at the bottom, warms it, then releases that warm air at the top. The heat is distributed throughout the house via heating ducts above. Upflow furnaces are almost always placed in basements or crawl spaces so the warm air is directed upward toward the living spaces of the home. But for homes on a slab, they are sometimes placed in the garage.
Generally, upflow furnaces are preferable to downflow furnaces because they are more efficient. However, if you don’t have a basement or crawl space, an upflow furnace just might not be feasible.
Upflow furnaces fall in the same price range - about $2,000 to $3,500 for a mid-efficiency model, including installation. The furnace itself usually costs $1,000 to $1,500, while labor adds an additional $1,000 to $2,000, depending on difficulty. Very high-efficiency models can cost $5,000 or more to buy and install.
- More efficient - Upflow furnaces tend to be more efficient than downflow furnaces because they take advantage of the natural tendency of heat to rise. And because they are more efficient, upflow furnaces are more likely to qualify for tax credits.
- More comfortable heat - Most people find the heat produced by an upflow furnace more comfortable because it heats the feet first. Downflow furnaces heat the upper portion of the body first.
- Easier to install - Upflow furnaces are typically easier to install because there’s no need for a subbase or special flooring.
- Not suitable for some homes - Upflow furnaces are not suitable for some types of homes, including mobile homes. In most cases, you need to have a basement.
Downflow or upflow is one of many decisions you’ll have to make when shopping for a furnace.
Energy efficiency is one of the most important decisions. With furnaces, energy efficiency is measured by annual fuel utilization efficiency (AFUE). If a unit has an AFUE of 80, that means 80 percent of the fuel is converted to heat while the other 20 percent is lost. For gas- and oil-fueled furnaces, the lowest efficiency rating allowed by federal rules is 78 percent (except in mobile homes, where the minimum is 75 percent). High efficiency units have an AFUE of 85 percent or greater.
Heat output, measured in British thermal units (BTUs), is equally as important. Common heat outputs include 40,000, 60,000, 80,000, 100,000 and 120,000 BTUs. The appropriate heat output is directly related to the size of your home - there’s only one number that works for each home. A furnace that is too large will not be energy efficient; one that is too small won’t provide enough heat. Consult a professional to find out which heat output is appropriate for your home.
Finally, you’ll have to decide on the type of fan motor: multi-speed or variable speed. With multi-speed, the installer can choose from multiple speed settings. With variable speed, the speed automatically adjusts as needed. Furnaces with variable speed motors are more energy efficient and provide better temperature control.
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