According to ACCA Manual S, furnace size should be within what percent of the peak heating load requirement?

The correct answer is that furnace size should be within 120% of the peak heating load requirement, as specified in ACCA Manual S. This guideline indicates that the furnace capacity should be appropriately sized to meet the heating demand during the coldest periods while accounting for potential variations and inefficiencies in the system.

Choosing a furnace that exceeds the peak load by up to 120% ensures that the system can effectively handle the heating requirements without short cycling, which can lead to increased wear on the equipment and reduced efficiency. The goal is to find a balance that provides sufficient heating without oversizing the unit, which could lead to excessive costs in both equipment and energy usage.

In scenarios where the options extend beyond 120%, such as 140% or 150%, a higher percentage would likely lead to comfort problems and financial inefficiencies due to overcapacity. The principle behind these guidelines is to achieve optimum performance and efficiency in residential and commercial heating systems, allowing them to function correctly without undue strain or expense.