Under the Michigan Energy Code, a new home has 2,400 square feet of conditioned floor area. What is the maximum allowable air leakage rate at 50 pascals pressure difference?
Correct Answer
D) 3.0 ACH50
The Michigan Energy Code requires new homes to achieve no more than 3.0 air changes per hour at 50 pascals (3.0 ACH50) for energy efficiency.
Why This Is the Correct Answer
The Michigan Energy Code requires new residential buildings to achieve a maximum air leakage rate of 3.0 ACH50 (air changes per hour at 50 pascals). This limit applies regardless of the home's square footage — it is an envelope performance standard measured by a blower door test. Michigan adopted this threshold to comply with energy efficiency targets that reduce heating and cooling loads in the state's cold climate.
Why the Other Options Are Wrong
Option A: 5.0 ACH50
5.0 ACH50 was the allowable limit under older versions of the energy code (IECC 2009 and earlier). Michigan has since adopted stricter requirements. Using 5.0 ACH50 would result in a non-compliant home under current Michigan Energy Code.
Option B: 7.2 ACH50
7.2 ACH50 is not a standard code threshold and represents a leaky, poorly sealed building envelope. This value exceeds even older energy code limits and would fail a blower door test under any current Michigan energy code requirement.
Option C: 4.0 ACH50
4.0 ACH50 is close to the correct answer but is not the Michigan Energy Code limit. While some green building programs (such as ENERGY STAR) have used intermediate targets, the Michigan Energy Code specifically requires 3.0 ACH50 for new residential construction.
Memory Technique
Remember '3 for new construction' — Michigan's current energy code allows no more than 3.0 ACH50. Think of the number 3 as representing 'third generation' tighter building science. If someone asks about the old code, it was 5 — twice as leaky. The square footage in the question is a red herring designed to make you overthink it.
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