Conventional vs fan: what's actually different?
A conventional oven heats with static elements — usually top and bottom — and the air inside moves only by natural convection: hot air rises, cool air sinks. That creates hot and cool zones, which is why the top shelf browns faster. A fan (convection) oven adds a fan — often around a third heating element — that circulates hot air continuously. The moving air strips away the cool boundary layer around your food, so heat transfers faster and more evenly. The practical result, confirmed by every major oven manufacturer: a convection oven conversion means cooking about 20°C (25°F) lower than the conventional temperature, for roughly 10% less time.
The 20-degree rule
The rule is simple enough to memorise: fan temperature = conventional temperature minus 20°C, and never below 120°C. Going the other way: conventional = fan plus 20°C. In Fahrenheit the equivalent is minus/plus 25°F. The 120°C floor matters because below it the fan's efficiency advantage breaks down and food-safety margins shrink — FanBake clamps conversions at 120°C and tells you when it has done so. Time follows a gentler rule: reduce by about 10%, and start checking a little early rather than trusting the clock blindly.
Why recipes disagree
If you have ever wondered why one recipe says 180°C and another says 160°C fan for the “same” cake, now you know: they are the same temperature, expressed for different ovens. European recipes increasingly give fan temperatures as standard; American recipes usually give conventional (often labelled just “°F”) and expect you to convert. Older ovens also run hot or cold by 10–15°C, so treat any conversion as a starting point and learn your own oven's personality with an oven thermometer — a $10 tool that improves every bake.
When to use fan (and when not to)
- Use fan for: roasting meat and vegetables (even browning all over), batch baking cookies across multiple shelves, anything where even heat matters more than a fierce bottom blast.
- Use conventional for: delicate cakes and soufflés that can be dried out or lopsided by moving air, bread where you want a fierce bottom heat for oven spring, and custards that need gentle, still heat.
- Multi-shelf baking is the fan oven's superpower — the circulating air means the top tray and bottom tray actually cook at the same rate.
Quick conversion table: everyday dishes
| Dish | Conventional | Fan | Notes |
|---|---|---|---|
| Victoria sponge | 180°C | 160°C | 25–30 min; check 5 min early |
| Chocolate brownies | 180°C | 160°C | Slight wobble in centre is fine |
| Shortbread | 160°C | 140°C | Low and slow; pale, not browned |
| Roast chicken | 200°C | 180°C | 20 min per 500 g + 20 min |
| Roast potatoes | 220°C | 200°C | Fan gives extra-even crisping |
| Pizza (home oven) | 240°C+ | 220°C+ | As hot as your oven goes |
| Meringues | 120°C | 120°C (min) | Clamped — dry low, don't rush |
| Bread loaf | 220°C | 200°C | Conventional often better for spring |
| Casserole / stew | 160°C | 140°C | Long, gentle; lid on |
| Cookies (multi-shelf) | 190°C | 170°C | Rotate trays once anyway |
Adjusting the time, not just the temperature
The 10% time reduction is a guideline, not a law. Dense items (a deep fruit cake, a whole turkey) need closer to the full conventional time because heat still has to penetrate to the centre. Thin items (cookies, flatbreads) feel the full benefit and can overcook fast — check them at 80% of the stated time. And remember the golden rule of baking: the recipe's time is an estimate, but colour, smell, and a skewer test are measurements. Start checking early; you can always bake longer, but you cannot un-bake.
Fan oven myths
- “Fan is always better.” Not for soufflés, delicate sponges, or anything where moving air dries the surface before the structure sets.
- “Just subtract 20 and change nothing else.” The temperature converts cleanly, but multi-shelf loads and dense items still need judgement on time.
- “All fan ovens are equal.” True fan ovens (fan + dedicated element) differ from fan-assisted ones (fan + top/bottom elements). Know which you own — the manual says.
- “Preheating doesn't matter with fan.” It still matters. The circulating air reaches temperature faster, but the walls and shelves need their heat too.
Converting American recipes
US recipes speak Fahrenheit and assume a conventional oven. The workflow: convert °F to °C (subtract 32, multiply by 5/9), then subtract 20°C for fan. So 350°F → 177°C conventional → ~160°C fan. FanBake handles the fan/conventional step; for the °F→°C step, remember the anchor points: 300°F ≈ 150°C, 350°F ≈ 180°C, 400°F ≈ 200°C, 450°F ≈ 230°C. Most recipes survive rounding to the nearest 10 degrees.
Food safety temperatures
Conversion never overrides safety: poultry must reach 74°C (165°F) internal, pork 63°C (145°F) plus rest, and reheated leftovers 74°C throughout. The 120°C fan floor exists partly for this reason — low-and-slow has limits. When in doubt, a probe thermometer beats every conversion rule ever written.
Getting to know your oven
Every oven lies a little. Buy an oven thermometer, hang it on the middle shelf, and compare its reading to the dial at 160°C, 180°C, and 200°C. Note the offset on a sticky note inside a cupboard door. From then on, apply your personal offset before converting — a recipe, a conversion, and a calibrated oven is the closest home baking gets to laboratory precision.
Fan oven symbols, decoded
Oven dials speak in hieroglyphs. The symbols that matter: a fan inside a circle = true fan (fan + dedicated element — the setting this converter is calibrated for); a fan with a line above/below = fan-assisted conventional (moving air plus top/bottom heat — convert the same way, but expect slightly fiercer browning); two horizontal lines = conventional top+bottom; one line = single element. If your oven only has fan-assisted and not true fan, the 20°C rule still holds — just watch the top of bakes a little more closely.
The science of moving air
Why does moving air cook faster? Around any food sits a thin boundary layer of still air that insulates it — heat must conduct through this layer before reaching the surface. A fan continuously strips the layer away and replaces it with hot air, so heat transfer jumps dramatically. This is also why fan ovens dry surfaces faster (great for roast potatoes, risky for custards) and why marinades and glazes caramelise more aggressively. Understanding the mechanism helps you improvise: anything where you want surface drying and even browning loves the fan; anything where you want a still, humid environment doesn't.
Roasting guide: fan temperatures that work
- Whole chicken (1.5 kg): 180°C fan, ~1 hr 20 min. Rest 15 minutes.
- Beef joint (medium-rare): 180°C fan, 20 min per 500 g. Rest half the cooking time.
- Pork crackling: start 220°C fan for 20 min, drop to 180°C fan. The initial blast is non-negotiable for crackling.
- Roast vegetables: 200°C fan, 35–45 min. Don't crowd the tray — steam is the enemy of crisp.
- Whole fish: 180°C fan, 20–25 min. The fan's even heat is ideal for delicate flesh.
For all roasting, the fan's even heat means you can load the oven confidently — two trays of vegetables cook as evenly as one, which is the real everyday win of convection cooking.
One last habit separates good fan-oven cooks from great ones: write the converted temperature on the recipe itself the first time you nail it. Within a few months you'll have a personal, oven-calibrated cookbook where every dish just works — no converter needed, though we'll be here whenever a new recipe lands in your kitchen.
Cooking at the extremes
The 20-degree rule covers the everyday middle, but ovens also work at the edges. Very low fan (120–140°C) is ideal for slow roasting tough cuts, drying meringues, dehydrating fruit, and overnight cooking — the circulating air prevents the stagnant humid pockets that make slow conventional cooking uneven. Very high fan (220°C+) suits pizza, flatbreads, and anything where you want aggressive browning; with a pizza steel or stone, the fan's even heat means the base and the topping finish together instead of the eternal home-pizza dilemma of burnt top or pale base. One caution at the top end: fats and sugars go from golden to bitter fast in moving hot air, so stay close during the last minutes. At both extremes the converter's job is the same — translate the recipe's conventional number faithfully, then let your eyes and nose handle the rest.