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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorSimonD
    • CommentTimeFeb 7th 2022
    As some of you may be aware, I've designed whole house natural ventilation for my house. It's been working fine and in the temporary kitchen, we've had no issues with excess moisture or smells. However, there's a distinct possibility building control is going to ask for some kind of mechanical extract for the new kitchen.

    Now, I'm keeping things simple in the new kitchen and not installing any wall cabinets and I also have a curved vaulted ceiling. I've been looking at a variety of cooker hoods that might fit in with the design, but there's something that doesn't resonate very well in the designs for me. Historically I always been underwhelmed by domestic cooker hoods as I find them generally noisy and ineffective. Also, if I opt for an externally ducted version, I'll be chucking a high volume of air out of the house and will also need to open additional vents around the house to balance the extract. We do a lot of cooking and baking so our last cooker hood was on so much of the time and that gets irritating.

    Instead, I've begun to consider a couple of different single room, wall installed and balanced MVHR units, both of which can provide the min. extract rate for kitchens. There are the potential units:


    The advantage with these is that they are significantly quieter than normal cooker hoods, less intrusive into the environment. Despite rubbing up againstmy own design principles, they could also provide a simple backup should the whole house natural ventilation ever need an extra helping hand. They also don't cost much more than some of the cookers hoods I've been looking at and by the time I've bought all the ducting/accessories etc. there's not much in it at all.

    Thoughts and experiences. Is there anything I'm missing other than fit a cheap quiet extractor fan with 30 or 60l/s extract rate and be done with it?
    • CommentAuthorCWatters
    • CommentTimeFeb 7th 2022
    We have MVHR and a cooker extract to the outside. Doesn't really seem to cause any issues.
    • CommentAuthorRobL
    • CommentTimeFeb 7th 2022
    The difficulty with kitchens is the grease. There's eventually a manky deposit onto kitchen extract filters, and I reckon the fans are relatively robust. Where would the mank go if you used one of those units, and how would you clean it?

    The Prana looks very interesting by the way, with CO2 monitoring built in. I noticed it said it might freeze up in winter, and there is some special mode you can select to help it. Reminds me of a HR25 (similar 2 fan thing) we had ages ago - that would freeze up and make a horrible noise every winter - nothing for it but to turn it off in the coldest weather sadly.

    We have a kitchen extract to outside (where does the air come from?), and whole house MVHR. And we have a woodburner that doesn't get a lot of action. I did once tried to light the woodburner with the cooker extracter on.... I won't be doing that again!
    When I fry fish with garlic, I need 200m³/h of extraction, for 4 minutes each side. That's rather more than the Lunos can do. The other 23.87 hours each day, I need only a few m³/h of ventilation, say 5.

    I think the heat loss during the short running period is negligible, and it is poor design to try to specify a 200m³/h fan to run at 5m³/h for 99.44% of its lifetime. So a separate extractor suits me best.

    Key things are to get a positive shutoff when the extractor isn't running, so warm air doesn't escape through rattly backflow shutters. Extract from immediately above the cooker, so smells and steam are captured at source not dispersed around the room. Low noise, so the chef can talk to the front-of-house staff. Hood height set so you don't bang your head on it. Several speeds, depending what's cooking tonight.
    • CommentAuthorrevor
    • CommentTimeFeb 8th 2022
    We have a ceiling set extractor in recirc mode and we have a boost switch for the MVHR near the cooker hob . The exhaust from the extractor is about 1.5m from the MVHR intake and it works well. I wanted to minimise the openings in my walls one of the reasons reason for doing what we did and any leakage from the fan to outside when not running. There does seem to be a fashion for low set hoods a tall person bangs their head against them and if smells escape around the sides then they end up on the ceiling. A flush to ceiling fan will eventually extract the air congregating at ceiling level.
    • CommentTimeFeb 8th 2022 edited
    Posted By: revorThere does seem to be a fashion for low set hoods a tall person bangs their head against them
    I never understand the very common fashion for hoods set horizontally above the hob so tall people can bang their heads as you say, and also short people can't reach the switches. We have both in our house. Building regs are partly to blame I think because of the stated minimum height above the hob, but there is a get out if you read carefully. We have an AEG hood that has a triangular cross-section and is mounted behind the hob, a whole 75 mm above it. There are other similar models by other brands. Being close to the hob also makes it easier to be sure the airflow is going where you want it.

    Our hood is recirculating but we hardly ever use it and it hasn't got greasy so far. The main MVHR extract is in the middle of the ceiling and that has a filter that we do clean every three/six months. We don't fry a lot though and we use very little oil when we do.

    edit: You can also get hoods that retract into the worktop of course, and I think I've seen some that retract into the ceiling.
    • CommentTimeFeb 8th 2022
    Building Regs Part F seem to be a bit confused at the moment. AFAICT there's a new version about to come into force but it refers to the Domestic Ventilation Compliance Guide from ten years ago that in turn refers to diagrams in the AD that no longer exist. The new AD no longer mentions passive stack ventilation, whilst the compliance guide does etc etc. So it seems to me that BC reaction is likely to all depend on how persuasive you are and how knowledgeable you appear.

    The Prano ventilator seems like it normally runs at a much faster rate than you will need. The Lunos one looks to have a choice of more sensible rates, but I've only glanced at them both.
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