Make-up air

Make-up air is the fresh air deliberately supplied to a space to replace the air an extraction system removes. It matters most in a commercial kitchen, where a hood pulls a large volume of air out continuously. If that extracted air isn't replaced with matching make-up air, the kitchen goes into negative pressure — and the symptoms are classic and often misdiagnosed: the extraction hood seems to 'lose suction', doors become hard to open or slam, the extract back-drafts, and cold or hot air gets sucked in from wherever it can (stairwells, the dining room, gaps). People blame the hood or its motor when the real problem is starved make-up air. Proper design balances the supply to the extract (often gently tempered so you're not dumping 45°C air onto the line), which keeps the hood capturing grease and smoke as intended and the space comfortable — it ties directly to the kitchen's air changes per hour and its static pressure. If a hood underperforms despite clean filters and a working fan, check the make-up air before replacing anything — it's a core part of proper kitchen equipment maintenance and commissioning.