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Comment by i80and | Hacker News Reader

It is extremely common, even default in the US in my experience, to not have vent fans not actually... vent. As a renter, I don't really get a choice in the matter.

Opening a window significantly is also pretty unfeasible most of the year.

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Do you also have a gas stove? I’ve lived in lots of places that have unvented blowers but none of them had gas. Would be against code in almost every city in America.

Yep, gas stove unfortunately. I can't speak to code, but most people I talk to share this experience -- I assume there's grandfathering at play.

It's just illegal and no one complained or enforced.

I just looked it up and section M1503.1 of the 2018 International Mechanical Code has an exception for range hoods which allows most to be used ductless. Some states, CA for example, don't allow this but the majority of states just follow the IMC code.

Where I am, it's called non-conforming and, unless there's a complaint, it doesn't become a problem until you pull a building permit AND a Building Official notices.

How much maintenance do those fans require to keep working well? I feel like the common thing is to basically not touch them, and they get pretty gross and don't seem to do much.

Edit: I got downvoted for this? I feel like I've seen a lifetime of these fans being decades old and in poor shape. I think you folks are vastly overestimating how many people clean those or replace the filter.

They're basically char filters, so if you wipe them and change the filters every 6 months or so you're good.

I'd be surprised if the average change time is any less than 5 years though.

Very little maintenance is required but not zero. If it gets gross, wash it.

You need to clean the filters regularly so they don’t become a fire hazard due to oil buildup; the better ones should have some kind of reminder system and will have filters that are dishwasher safe.

I had a blower that recirculated with a gas stove in NYC, in a newish (2008 I believe) building.

New construction in NYC bans gas stoves.

The last 2 houses I have lived in both had gas stoves and unvented blowers. Both recently built.

In new construction people are installing those microwave vents that literally do nothing except blow the air out the top of the microwave. It’s not totally worthless but it’s next to worthless.

Then the cabinets above the microwave get coated with a sticky layer of polymerized(?) oil - even quicker than they normally would. It's gross.

New construction person in B.C. here.

We use them all the time and if they're not vented properly, we don't get occupancy. The HVAC designer or Engineer on the job wouldn't have it any other way.

Microwaves can vent if you hook up its vent to a duct, cheap construction doesn't do that if they can get away with it.

Yes and no, while I suppose you could technically attach a vent to the top half of the microwave and route it outside the upper vents are absolutely not designed for that and you would have the most awkward ugly installation that blocks your upper cabinet doors. So yes the reason for these units is 100% penny pinching and cheap construction but better construction alone won’t fix the problems with these microwaves.

"you would have the most awkward ugly installation that blocks your upper cabinet doors"

No, you route it through the cabinet and if you don't want it to look ugly then you build a chase around it. I usually don't since the chase takes up more room, and no one really cares as it's in the cabinet.

And yes they are designed for venting outside, that's what these are for: https://www.homedepot.com/p/Master-Flow-3-1-4-in-x-10-in-x-7...

We’re talking about two different kinds of microwaves. There are the ones you describe where the vent is inside the upper cabinet, those are designed to be vented outside. Then there’s the microwaves where the vent is in front of the cabinet doors, runs along the whole length of the microwave and blows up at the outside of the upper cabinet doors. There is nowhere you could even route it because anything on top of the microwave to capture it would physically block the doors from opening.

I see many of them that simply vent into the attic. This requires a properly vented attic, and has the downside of introducing moisture into the attic, which can lead to damage.

That said, mobile homes pretty much always vent outside in my experience.

A lot of them do not vent at all. They just draw it up through a coarse filter and out the top again.

Yes, I see those too. I work on houses for a living though and those are not too common, at least around here. I typically might see those in the older houses, or in half assed renovations.

Those fans can be installed in two ways, venting or recirculating. In a recirculation mode you need to keep the filters clean, and they do an _ok_ job at keeping smells out of the kitchen, but if they don't vent outdoors then you need to open a window unfortunately

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