Whole-House Ventilation Mechanical rate = 7.5*NP *Afloor NP default is number of bedrooms + 1 Use actual occupancy if higher Assumes infiltration rate of 0.02*Afloor No differentiation between mechanical ventilation system types
Local Exhaust Ventilation Bathrooms (not half bathrooms) 50 CFM on-demand, or 20 CFM continuous. Kitchen 100 CFM on-demand, or 5 ACH continuous, based on kitchen volume.
Can comply using a single fan through alternative compliance appendix Three steps Base fan flow rate Adjustment for local exhaust deficits Infiltration credit Existing Buildings
Base Fan Flow Rate Floor Area (ft 2 ) Bedrooms >7 < – – – – > or can use 7.5*NP *Afloor
Local Exhaust Deficits In each room where local exhaust should be, determine deficit relative to intermittent rate How much less than 50 cfm in bathrooms How much less than 100 cfm in kitchens For each room with a deficit, reduce rooms deficit by 20 cfm if that room has an operable window (not to drop below 0)
Local Exhaust Deficits Add up deficits, divide by 4 Add the result to the whole-house requirement This becomes the new whole-house requirement
Local Exhaust Deficits For existing fans being used, sound and ducting requirements not applicable Must measure flow if ratings dont exist or duct sizing cant be verified If only have rating at 0.10 in. wc but not 0.25 in. wc, can reduce rating at 0.10 in. wc by 25%
Local Exhaust Deficits Example #1 3 BR, 1500 sq. ft. house BR MBT BT KIT Deficit = = 200 Add 200/4 = 50 Whole-house requirement = = 95 cfm
Local Exhaust Deficits Example #4 BR MBT BT KIT Deficit = = 98 Add 98/4 25 Whole-house requirement = = 70 cfm 32 cfm Add whole-house fan here
Infiltration Credit IF House built before adoption of 62.2 Blower door test done Estimated infiltration using Standard 136 is greater than 2 cfm/100 sq. ft. THEN Reduce whole-house rate by ½ of the excess above 2 cfm/100 sq. ft.
Infiltration Credit Example #5 BR MBT BT KIT Std. 136 estimates inf. = 70 ½ * (70-30) = 20 Whole-house requirement = = 25 cfm (plus any deficit adjustment)
Infiltration Credit Example #6 BR MBT BT KIT Std. 136 estimates inf. = 120 ½ * (120-30) = 45 Whole-house requirement = = 0 cfm (plus any deficit adjustment)
Std. 136? Requires CFM50 Number of 8-foot stories (e.g. a 12-foot ceiling counts as 1.5) Weather factor w Weather factors can be found in BPI-101 standard
Std. 136 Approximation From Workforce Guidelines Appendix Assumes that volume = floor area * 8 # stories S