nz housing is on the slippery slope of failure.

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#3357078 24-Mar-2025 22:31

neb:

gzt: Many apartment style dwellings are specified and built with recirculating rangehoods. Hopeless. There is no external vent. Heat returns to the living space.

Is it "specified with" or just "the builders stuffed the other end of the duct into wherever there was a gap"? I've seen several of those, what looks like ventilation but that doesn't vent anywhere.

IMO The council inspectors should be picking up that sort of thing during inspections. However I don’t think they publicly list exactly what items are checked at inspections.

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#3357351 25-Mar-2025 20:08

neb:
gzt: Many apartment style dwellings are specified and built with recirculating rangehoods. Hopeless. There is no external vent. Heat returns to the living space.
Is it "specified with" or just "the builders stuffed the other end of the duct into wherever there was a gap"? I've seen several of those, what looks like ventilation but that doesn't vent anywhere.

Specified. Random example: https://www.noelleeming.co.nz/p/fisher-paykel-60cm-wall-rangehood/N148615.html - "External Top extraction - or recirculation front extraction"

Consumer guide says recirculation is a built-in option with many rangehoods. If you're placing a building size order no doubt it's even easier out of the box.

gzt

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#3357355 25-Mar-2025 20:24

tweake:
gzt: Many apartment style dwellings are specified and built with recirculating rangehoods. Hopeless. There is no external vent. Heat returns to the living space.

and so does all the pollutants. cooking is one of the biggest generators of pollution inside a house.

The recirculating units do have filters. In my experience the main metal mesh filters did catch at least some proportion of vaporized cooking oils because those visibly built up in and around the washable filters. Some units have additional carbon filters on the output which will help a little. In all cases the filters can have no effect on heat by design. Heat is vented directly into the living space.

gzt

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#3357363 25-Mar-2025 21:04

SomeoneSomewhere: Again, ventilation, stack effect, whatever cannot get you below outside air temperature,

It's also true that if you have little or no ventilation for internal heat sources, you will easily get inside air temperatures well above outside air temperatures.

SomeoneSomewhere

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#3357374 25-Mar-2025 22:58

Internal heat sources are typically a tiny fraction of external heat sources unless you're a commercial kitchen, a server room, or have very high human occupancy.

Apartments have a higher ratio of internal to external heat load, not because the internal load is higher, but because the external load is lower. You only have 1-2 faces exposed to outside air/insolation, rather than 4-5 on a typical house. Considered as a whole building, it's a surface area to volume ratio (square-cube law) problem.

The fundamental assumption here is that people want cooling below ambient. That implies AC at least some of the time. The moment you do that, ventilation begins raising the temperature, not lowering it.

Handle9

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#3357377 26-Mar-2025 00:46

tweake:

however doing vents on high rise buildings comes with challenges as each level is at a different pressure.

Not at all. That is why it's a requirement to do an air balance.

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#3357378 26-Mar-2025 00:48

gzt:

k1w1k1d: A properly designed and built house with insulation should not overheat.

Many apartment style dwellings are specified and built with recirculating rangehoods. Hopeless. There is no external vent. Heat returns to the living space.

That has 3/16 of nothing to do with overheating. Recirculating rangehoods can cause air quality problems, they don't cause overheating.

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#3357390 26-Mar-2025 07:58

SomeoneSomewhere: Apartments have a higher ratio of internal to external heat load, not because the internal load is higher, but because the external load is lower. You only have 1-2 faces exposed to outside air/insolation, rather than 4-5 on a typical house. Considered as a whole building, it's a surface area to volume ratio (square-cube law) problem.

Apartments are typically much smaller than a dwelling. Recirculating rangehood, washing/dryer combo, dishwasher, shower, sometimes an oven. These are all heat sources. Internal heat generated per square meter is far higher. The multilevel town house style some developers want insulation values reduced from have similar problems and more opportunities for resolution either at design time or remedial work.

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#3357391 26-Mar-2025 08:03

Handle9:That has 3/16 of nothing to do with overheating. Recirculating rangehoods can cause air quality problems, they don't cause overheating.

You might reasonably argue a recirculating rangehood is not a heat source. The actual heat comes from the cooking elements. Other than that the effect is entirely the same.

The recirculating rangehood does not vent any heat outside the building envelope.

johno1234

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#3357394 26-Mar-2025 08:28

Be that as it may, the whole concept of a recirculating range hood strikes me as a crock. Bathrooms are required to have mechanical venting aren't they? Kitchens should be the same.

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#3357395 26-Mar-2025 08:29

gzt:

Handle9:That has 3/16 of nothing to do with overheating. Recirculating rangehoods can cause air quality problems, they don't cause overheating.

You might reasonably argue a recirculating rangehood is not a heat source. The actual heat comes from the cooking elements. Other than that the effect is entirely the same.

The recirculating rangehood does not vent any heat outside the building envelope.

How much heat do you think an extract rangehood actually removes from the space? It’s not a lot at all.

Rangehoods exist to remove cooking smells and fumes. They don’t exist to control the temperature of a space.

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#3357397 26-Mar-2025 08:51

johno1234:

Be that as it may, the whole concept of a recirculating range hood strikes me as a crock. Bathrooms are required to have mechanical venting aren't they? Kitchens should be the same.

Generally if you have opening windows in the bathroom the building code doesn’t require mechanical ventilation

tweake

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#3357429 26-Mar-2025 11:30

gzt:

The recirculating units do have filters. In my experience the main metal mesh filters did catch at least some proportion of vaporized cooking oils because those visibly built up in and around the washable filters. Some units have additional carbon filters on the output which will help a little. In all cases the filters can have no effect on heat by design. Heat is vented directly into the living space.

the filters only catch big stuff. all the fine stuff and gases stays in the air.

this is why passive house has gone away from recirc range hoods (well except nz where they still use them to cut costs).

richms

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#3357440 26-Mar-2025 12:44

The carbon ones will get loads of stuff, the problem is that its full almost immediately that you start using it and no-one ever changes them.

Richard rich.ms

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#3357455 26-Mar-2025 13:30

Handle9: How much heat do you think an extract rangehood actually removes from the space? It’s not a lot at all.

Lots and lots. An externally vented rangehood removes tons of heat. Essential in summer.

My rangehood externally vents in normal circumstances. There was a problem. I noticed the house was getting stupidly hot with the rangehood on. Later I noticed air was blowing out of it near the ceiling. On removing the cover I found no retainer was fitted to the motor/hose during installation and the vent hose was now detached from the motor. The unit was blowing all the heat out at ceiling level. Fixed the hose retainer. House temperature problem solved.

As a bonus in summer we run the rangehood when the oven is in use. It is surprisingly effective at keeping internal temperatures down by removing a proportion of the hot air generated by the oven and venting that externally.

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