How Buildings Lose Heat, Part 2: Convection
Air leaks lose as much energy as poor insulation — often more. But moving air plays by different rules: every leak can only be seen from one side of the building.
New to the series? Start with Part 1: Conduction.
In a heated building, warm air rises and escapes high up, while cold air is drawn in low down. In between sits the neutral plane, where there’s no net airflow.
Cold air coming in. Look for cold spots at floors, wall bases, window and door casings and power outlets. Image from inside.
Warm air going out. Look for warm streaks along rooflines, spandrel joints and panel seals. Image from outside, out of direct sun.
If the HVAC system keeps the building under positive pressure, even cool air can be seen escaping on a warm day. Direction follows pressure, not just temperature.
On a calm day, small leaks may not move enough air to show up. A blower door fan pressurises or depressurises the whole building, turning marginal leaks into obvious ones — and the thermal camera shows exactly where they are.
Roof soffits can let outside air into wall and ceiling cavities, and the thermal pattern often looks backwards. It’s a common cause of comfort complaints and, in cold climates, pipe freeze-ups that owners can’t trace.
It’s rarely visible from outside. Finding it takes an interior inspection, often with a blower door. Site Matrix can assist with all site preparatory works including site blower testing.
Wind, fans and HVAC systems create forced convection. The same in/out logic applies, but the side you inspect from changes:
The same applies to air-cooled condensers and other plant under negative pressure.
Wrong side, wrong time of day, wrong pressure assumptions — and the report looks spotless while the real leak goes unfound. Every inspection we run starts with one question: which mechanism are we chasing, and what does that mean for where we point the camera?
Anyone can point a camera at a wall. We plan the inspection around the physics — so it finds what’s really there.
Our Energy Analysis covers facades, whole-building air leakage and mechanical plant — with a located, imaged report for every finding.
Conduction explains how heat moves through the material.
Convection explains how air carries it out.
Together, they show exactly where your energy is going.
