Built-in microwave ventilation

If you have somewhere (false ceiling, top of cupboards?) to duct it away and use a ducted fan you can get rectangular duct about 4cm in one dimension, use stop end and cut out the side of the duct. All standard, so cheaper; and gets rid of cooking smells/fat.

Maybe you just need ventilation holes (and a covering grille plate) as the fan inside the microwave itself will push the hot air out if the holes are correctly positioned.

Had you considered putting a false back on the cupboard above and effectively creating a chimney? If the cupboards stop short of the ceiling then the hot air will vent easily, if not you'll need to duct it through the top cupboard to a grill. Don't forget to provide an inlet. Alternatively, could you adapt one of the standard microwave fixing kits which have grills?

It's not practical to expel the air other than out the front. As for smalls/fat, they shouldn't be any worse than a microwave on the countertop, and people are happy with those.

At the moment there's a big hole with the dimensions I gave. But it has to cope with air intake and outlet. So I was hoping for something with a grille and fan, to assist the circulation from the microwave's internal fan (to help stop that recirculating air back into the oven's intake inside the wall unit)

That's a possibility, but I was trying to avoid all those new holes.

I suspect this one (I have the bezel) once had a grill, but it's been misplaced. If I'm fitting a new one, it'd be handy if it had fan assist.

Roland Perry brought next idea :

Could you not manage to add a partition so the intake and outlet are separated, to ensure there is some flow rather than recirculation of the same air?

I'm lost. Wouldn't you be buying a microwave designed for building in? That'll have ducts built into the microwave.

I don't know how much it matters if there's no ventilation, assuming it's say an 800w microwave, used for a couple of minutes at a time?

In message <rcl3e2$i5m$ snipped-for-privacy@dont-email.me, at 14:37:05 on Sat, 20 Jun

I'd still need a grille at the front for the airflow.

The intake is at the rear of the RHS, and there are two outlets: one at the front of the RHS for the electronics, and another in the top for the cooking chamber.

Unfortunately, the RHS of the oven is against a brick wall.

I might be able to run some trunking from the rear LH corner (where I could stick a vent to the room), along the back, and round the corner to the inlet. Plan view:

==========================# vent ------trunking -----+ # | mmmmmmmmmmmmmmmmmmmmmm+ # | m <+ # | m <- # wall | m m # | m m # | m >>>>>> > # | m >>>>>> > # | mmmmmmmmmmmmmmmmmmmmmm # ___ door ____#

facing room

To the left is free space.

In message <rcl7tb$c6k$ snipped-for-privacy@dont-email.me, at 15:53:30 on Sat, 20 Jun

I've got one that works OK already (1000w), even if designed for countertop.

Given that we've had no kitchen since before lockdown we've been exploring the various settings, one of which is a conventional oven.

Also things like Combination/Jacket Potatoes etc have the thing on for half an hour.

Roland Perry submitted this idea :

A passive system is a better bet than an active one, if it can be arranged. You only need to duct one - the intake or the outlet, the other will find its own route.

In message <rclimj$dj1$ snipped-for-privacy@dont-email.me, at 18:57:38 on Sat, 20 Jun

As there's one inlet and two outlets...

Still need a grille for the front though.

I can see why you're concerned.

I know it would be usual to vent the warm air upwards, but as this is a fan duct, you could also take it downwards or sideways if that works better. If the air is just hot, not moist, it may not matter much where it ends up - behind the plinth at the bottom of the units, for example.

Put mesh over it though or nasty insects come in. Brian

In message <rclvhk$rnd$ snipped-for-privacy@dont-email.me, at 22:36:50 on Sat, 20 Jun

Because there are items in the same set of units which need to be kept at room temperature.

I was proposing an intake duct, the outlet straight into the room. But I need something to fill the 4x57cm slot, and was thinking something with fan assist might be helpful.

The main hot air exhaust is at the op of the microwave, so "down" is difficult.

That's a possibility. See my earlier diagram, maybe an outlet on the LHS as well. I could probably fit a fan scavenged from a computer PSU on the inside. Now, if it was possible to power that off the same supply as the interior light, we could have a solution.

That area's pretty airtight.