Mechanical Code Changes for 2015 Michigan Residential Code
New residences will required to have a whole house ventilation system. R303.4 Natural Ventilation is no longer acceptable. Unless house has an air exchange rate 5 ACH or more, which would then be a violation of the energy code which requires an ACH rate of no more than 4. WHOLE-HOUSE MECHANICAL VENTILATION SYSTEM. An exhaust system, supply system, or combination thereof that is designed to mechanically exchange indoor air for outdoor air where operating continuously or through a programmed intermittent schedule to satisfy the whole-house ventilation rate.
Duct systems located in attics will required duct pressure testing. N1103.3.3
All duct joints will have to be sealed. Duct seams which are button lock, or snap lockseams will have to be sealed also. M1601.4.1
Whole house ventilation efficiency for bath fans and air handler units must have an efficiency of 2.8 CFM per watt. Furnace blower motor is allowed to be ECM type motor to meet this requirement. N1103.6.1
Venting of Bath fans have limited lengths for ductwork per Table M1506.2. Fans also must be capable of producing .25" WC for the required CFM. Bath fans must have minimum capacity of 50 CFM intermittent or 20 CFM continuous. Kitchen exhaust fans must have a capacity of 100CFM minimum.
Ventilation rates for whole house system (Outside Air) is per table M1507.3.3 (2).
Return air systems can no longer use building framing cavities for ducts or plenums. Return air must be done sheet metal or other approved duct materials. N1103.3.5
All furnaces and Air handling unit s must comply with ASHRAE standard 193 for air leakage rate not more than 2%, and must state this in equipment literature. N1220.127.116.11
Whole ventilation system must operate in a continuous mode or have a control which cycles the 25% in a 4 hour segment which require more ventilation air per table M1507.3.3(1).
Pre fabricated metal solid fuel fireplaces chimneys cannot have elbows that exceed 30 degrees from the vertical, and the chimney cap must be pitched 10 degrees to allowed drainage of water, and shall lap down 4". R1005.4 R
There are other changes in the code, it is strongly recommended that contractors obtain a copy of the code and become familiar with all the changes.