The second appliance in the oven column is a harder decision than the first. A main oven is a main oven. The compact slot above it can be a microwave, a combination oven, a steamer or a small conventional oven, and they are genuinely different tools.
The cabinetry decides part of it for you, so start there.
Three apertures, and they are not interchangeable
- 560 x 380 x 550 mm: built-in microwaves. The Bosch BEL554MS0K and BEL554MB2M sit here. The Fujioh FV-MW51 needs 560 x 380 x 500 mm.
- 560 x 450 x 550 mm: compact ovens, combis and steamers. The Bosch CMG7241B1, CMG7361B1B, CSG7584B1 and CDG714XB1 all use it. The Fujioh FV-AL81 needs 560 x 450 x 540 mm.
- 560 x 575 to 600 x 550 mm: full-height ovens, including microwave-combination models like the Bosch HMG7361B1.
A microwave will not fill a 450 mm opening and a compact oven will not go into a 380 mm one. If the cabinetry is already built, that single measurement narrows the field before you look at anything else.
Built-in microwave
The Bosch BEL554MS0K and BEL554MB2M are 25 litres with a grill, drawing 1450 W through a supplied plug on a 10 A fuse. The Fujioh FV-MW51 is also 25 litres with a grill and is marked 13 A.
This is the low-commitment option. It reheats, defrosts and grills, it plugs in, and it needs the shallowest opening. Twenty-five litres is genuinely small though, and a large dinner plate is a tight fit in some of them.
Compact combination oven
A real oven with a microwave function on top. The Bosch CMG7241B1 and CMG7361B1B are 45 litres in the 450 mm aperture, and the Fujioh FV-AL81 is 46 litres.
This is the format most people should be looking at. You get conventional and fan cooking, plus microwave for speed, in a cabinet that also fits a plate properly. The catch is power: both Bosch models are rated 3600 W on a 16 A supply, so they need a dedicated circuit rather than a socket.
Steam and combi steam
The Bosch CDG714XB1 is a pure steamer at 38 litres, drawing 1750 W on a 10 A fuse, which makes it one of the easier compact appliances to install. The CSG7584B1 is a 47 litre combination steam oven at 3300 W on 16 A.
Mayer offers larger combi steam units, the MMSO15-RG at 50 litres and the MMSO17-RG at 72 litres.
Steam is worth taking seriously if you cook a lot of fish, vegetables or dim sum. Reheating rice in a steam oven is a completely different result to reheating it in a microwave, and that alone converts people. It is a poor choice as your only second appliance if what you actually want is speed at 7pm on a Tuesday.
Or put it in the main oven instead
The Bosch HMG7361B1 is a full-height 67 litre oven with a microwave function built in, using a standard 560 x 585 x 550 mm aperture. If you have one cabinet opening rather than two, this gets you both functions without a second unit.
You give up a little capacity against the 76 litre conventional ovens, and you cannot use both appliances at once, which matters more than it sounds when you are cooking a full meal.
Power, summarised
This is where the formats really diverge, and it decides how much preparation work you need:
- Microwaves: 1450 W, plug supplied, 10 A. Uses a socket.
- Pure steamer, Bosch CDG714XB1: 1750 W, 10 A. Uses a socket.
- Compact combi and combi steam: 3300 to 3600 W, 16 A. Dedicated circuit, licensed electrician.
If the electrical work is not happening, that list makes the decision for you.
A note on stacking
If you are putting a compact appliance above a main oven, both need their own aperture and their own supply. The carpenter needs both cutout figures in writing, and the electrician needs to know whether you are running one 16 A circuit or two.
Get that sorted at the drawing stage. Retrofitting a second circuit into a finished oven column is unpleasant work.
Where to look
Everything above lives in microwaves and combi ovens, except the full-height combination models, which sit with the built-in ovens. If your opening is 560 mm wide and you already know the height, that is the fastest filter.
What you would actually cook in one
Specifications only get you so far. These four recipes are built around the appliances above, and they are a better test of whether you want steam than any feature list:
- Teochew steamed seabass in a steam oven, the dish that converts most people to steam.
- Double-boiled chicken soup, which runs for three hours and shows you where the water tank limit bites.
- Steamed egg with minced pork, with the steam-oven and microwave methods compared side by side.
- Har cheong gai using the air fry function, if the compact slot is doing double duty.
Common questions
What size opening does a built-in microwave need?
560 mm wide by 380 mm high by 550 mm deep for the Bosch BEL554 models. The Fujioh FV-MW51 needs 560 x 380 x 500 mm. Compact ovens and combis need a taller 450 mm opening and will not fit a microwave aperture.
Is a combi oven better than a microwave?
It does more, at 45 litres against 25, with real oven cooking as well as microwave. It also costs more and needs a 16 A dedicated circuit rather than a socket. If you have the cabinet height and the electrical supply, it is the better appliance.
Do I need a steam oven if I already have a main oven?
Only if you cook the sort of food steam is good at. Fish, vegetables, dumplings and reheating rice all come out noticeably better. For roasting and baking, your main oven already has it covered.
Can a built-in microwave sit on a shelf instead?
Built-in models are designed for a cabinet aperture with specific ventilation. Standing one on an open shelf can block its air path. If you want a countertop appliance, buy one designed as a countertop appliance.
Which needs a licensed electrician?
Anything rated 16 A, which covers the Bosch compact combi and combi steam models at 3300 to 3600 W. The microwaves and the CDG714XB1 steamer are 10 A with plugs and can use a socket.