How much heat does a person add to a room?

A sedentary office worker adds about 250 BTU/hr sensible heat and 200 BTU/hr latent heat (moisture) for a total of 450 BTU/hr. A person doing light work adds 250 BTU/hr sensible and 350 BTU/hr latent. Someone exercising at a gym adds 265 BTU/hr sensible and 935 BTU/hr latent — total 1,200 BTU/hr per person. The split between sensible and latent matters because latent load drives dehumidification requirements and affects the sensible heat ratio of your cooling system.

Why is occupant heat gain so important for gyms and restaurants?

Gyms and restaurants have the highest occupant density and activity levels of any building type. A 2,000 sq ft gym with 30 people exercising adds 36,000 BTU/hr of heat gain from occupants alone — more than the envelope load on a mild day. Restaurants add cooking equipment, lighting, and dense occupancy simultaneously, creating peak loads that can be 3-4 times the envelope load. Systems sized only on building envelope calculations will be massively undersized for these occupancies. Always calculate occupant load separately and add it to envelope loads.

👥 Occupant Heat Gain

People Heat Gain Calculator

Calculate sensible and latent heat gain from building occupants using ASHRAE Handbook activity levels. Critical for offices, gyms, restaurants, classrooms, and any space where people are the dominant cooling load. Results feed into your cooling load calculation.

Unit System:

👥 Occupancy Details

Number of People * Use peak occupancy for design — not average.

Activity Level *

Occupancy Factor i

0-1

Sensible Heat / Person *

BTU/hr

Latent Heat / Person *

BTU/hr

Radiant Fraction i

0-1

ASHRAE Handbook Reference Values (BTU/hr per person at 75°F room temp)

Seated at rest	245 sensible / 205 latent
Office work	250 sensible / 200 latent
Restaurant	275 sensible / 275 latent
Classroom	295 sensible / 255 latent
Light bench work	305 sensible / 475 latent
Heavy gym exercise	265 sensible / 935 latent

👥 Occupant Heat Gain Results

Component	Per Person	Total	% of Total

Export:

When people are the biggest cooling load in the room

For offices, gyms, classrooms, and restaurants, occupants are frequently the single largest source of cooling load — larger than lights, equipment, or even solar gain through windows. A yoga studio with 25 students doing hot yoga can generate over 30,000 BTU/hr of heat from occupants alone. An HVAC system sized on envelope loads only will fail within the first week of operation. This is why occupant load calculations are non-negotiable in ASHRAE and ACCA cooling load procedures.

Sensible vs. latent: why it matters for your system selection

Sensible heat raises air temperature. Latent heat adds moisture to the air. A gym full of people exercising produces far more latent heat than sensible heat — that's why gyms feel humid even when the temperature is controlled. This high latent fraction requires an HVAC system with a low sensible heat ratio (SHR) and strong dehumidification capacity. A standard residential AC with SHR of 0.75-0.80 will keep the temperature acceptable but the space will feel clammy and smell bad. You need a unit with SHR of 0.65 or lower for high-latent spaces. Use the SHR calculator to verify your equipment selection.

Occupancy factor: don't oversize for empty rooms

ASHRAE allows applying an occupancy factor (0 to 1.0) to account for the fact that spaces are rarely 100% occupied during the design hour. For a 50-person office, peak concurrent occupancy might be 40 people (factor 0.80). For a restaurant, the dining room fills completely at lunch peak (factor 1.0). Using the right occupancy factor prevents equipment oversizing, which causes short-cycling, poor humidity control, and comfort complaints in Canadian climates where humidity management is critical May through September.

Frequently Asked Questions

My office AC can't keep up in summer — could it be occupant load?+

Yes — this is one of the most common reasons commercial HVAC systems struggle in summer. A 20-person office generates 9,000 BTU/hr of sensible heat and 4,000 BTU/hr of latent heat from occupants alone. If the original system was sized only on envelope loads or for a different occupancy, it will be undersized for peak occupancy. Check whether the problem occurs specifically when the office is full (lunch hour, 2-4 PM on hot days) or all the time. If it's occupancy-correlated, calculate the actual occupant load here and compare it to what the system can handle. Adding supplemental cooling or upgrading to a larger system may be needed.

How do I calculate occupant load for a restaurant in Canada?+

Use the restaurant activity level (275 BTU/hr sensible, 275 BTU/hr latent per person) at peak occupancy. Canadian building codes set restaurant occupancy at 1 person per 1.0-1.2 m² of dining area for load purposes. A 100 m² dining room has a design occupancy of 83-100 people. At 100 people: sensible load from occupants = 100 x 275 = 27,500 BTU/hr, latent = 27,500 BTU/hr. Add kitchen equipment heat gain, lighting, and envelope loads for total cooling load. Many Canadian restaurants are severely underserved by HVAC because kitchen loads and dining occupancy weren't calculated correctly during design — particularly a problem in older strip-mall restaurant conversions.