CSLB C-20 HVAC ContractorPlanning and LayoutEasy
A Manual J load calculation for a 3-bedroom home uses the standard default occupancy formula of (bedrooms + 1) to estimate the number of occupants for internal heat gain purposes. Using a typical Manual J allowance of 230 Btu/hr sensible heat gain per person, what is the total occupant sensible heat gain added to the cooling load?
- A920 Btu/hr
- B1,380 Btu/hr
- C1,150 Btu/hr
- D690 Btu/hr
Show answer & explanationAnswer & explanation
Correct answer: A. 920 Btu/hr
Default occupancy = bedrooms + 1 = 3 + 1 = 4 people. Occupant sensible gain = 4 people × 230 Btu/hr = 920 Btu/hr. This value is added to the internal gains portion of the cooling load.
Why the other options are wrong
- B. Uses 6 occupants, far above the standard default.
- C. Uses 5 occupants (bedrooms+2), overcounting.
- D. Uses only 3 occupants (bedrooms without the +1 rule).
Manual J Occupant Load
Manual J estimates internal sensible heat gain from occupants using a default occupancy count of bedrooms plus one, multiplied by a standard per-person Btu/hr allowance.
- Default occupancy = bedrooms + 1
- Standard sensible gain ≈ 230 Btu/hr per person
- Occupant gain is added to internal gains, separate from appliance loads
Memory trick: Bedrooms plus one, times 230, sums the sun (people) load.