Which statement is true regarding mid-efficiency gas-fired furnaces?

Mid-efficiency gas-fired furnaces are designed to operate with an efficiency range typically between 80% to 89%. One of the key characteristics of these furnaces is their venting system, which can be configured for various installation options.

The statement regarding venting through the sidewall is accurate because mid-efficiency furnaces are often vented using a single-wall metal pipe. This allows for more flexible installation options, including horizontal venting through the sidewall, which is advantageous in certain situations where vertical venting (through the roof) is impractical. This feature helps in facilitating the efficient expulsion of combustion gases and is a common practice in modern installations.

In contrast, other statements present characteristics that are not universally applicable to mid-efficiency models. While condensate tubing might be found in high-efficiency models that use condensation in the venting process, mid-efficiency furnaces typically do not produce significant condensate. Although some mid-efficiency furnaces can be equipped with induced draft fans, it's not a standard requirement for all models. Lastly, plastic venting materials are generally associated with high-efficiency units, as they are designed to safely vent the lower temperature exhaust gases produced by condensing models, not mid-efficiency furnaces.