MHRV and boost button

[JamieM]

 

Our electrician has hesitations about putting a boost switch for the MHRV in bathrooms and suggested using a pull cord.  I mentioned to our MHRV supplier and got told that a boost switch with 240v or 10v could be installed within the bathroom as long as its retractable.

 

I’m going to mention to my electrician but could anyone explain what this means to me (in layman’s terms as I’m an idiot sometimes).

 

Thanks

 

Jamie

[ProDave]

I think a lot depends on the particular mvhr unit, whether any built in switching function is 240V or some lower voltage.

 

Also do you jut want a boost on / off switch or a timer?

 

Personally I am just going to install one of those Horstman immersion heater boost timer switches outside each bathroom, and one in the kitchen. You press the button one or more times to select the boost time that you want it to stay on for. These will collectively switch a relay that will switch the volt free contacts of my particular mvhr unit.
 

[Temp]

I'm not sure what "retractable" refers to but..

 

In my experience Electricians are generally nervous about putting anything mains powered in a bathroom. Sometimes they are reluctant to do so even when the regulations allow. Typically they prefer wall mounted light switches to be outside but accept pull switches for things like lights and fans inside.

 

As far as I can tell you can put a mains powered switch, appliance or thermostat in a bathroom provided..

 

a) It's in the right "zone" and

b) It's installed in accordance with the manufacturers instructions.

 

The latter is frequently the problem - many switches, appliances and thermostats are not approved by the manufacturer for use in humid locations so you are precluded from installing them in a bathroom.

 

In short - if you can find an MHRV boost switch that the maker says can be installed in a humid location then it should be ok.  

 

 

 

 

 

[Temp]

According to this...

https://www.amazon.co.uk/Schneider-Electric-Screwless-Retractive-Stainless-x/dp/B003NVKJMM/ref=sr_1_1?ie=UTF8&qid=1485361485&sr=8-1&keywords=retractive+light+switch

 

Quote

A retractive switch automatically returns to its rest position once pressed and provides a momentary electrical signal, not a continuous signal as in a normal switch.

 

Most people call those momentary switches. I don't see how that helps you meet the regulations for switches in bathrooms. My guess is that your MHRV system needs a momentary switch to trigger boost mode and that this has nothing to do with the regulations.

 

 

 

Edited January 25, 2017 by Temp

[joe90]

I had not thought of a boost button for mine but thought the humidistat within the unit would suffice?

or are you thinking of a boost as well?

Edited January 25, 2017 by joe90
Edit

[dogman]

Have you looked at a roof mounted pir to switch it to boost when you enter. Most work on a N/C or N/O low voltage circut

[Temp]

I've had a quick look online and I can't find a nice looking momentary rocker/pushbutton mains switch that's approved for use in a humid area. There are lots of IP65 rated switches intended for outside use but they don't look very pretty. 

 

This looks like the sort of momentary/retractable pull switch your electrician is talking about..

 https://www.tlc-direct.co.uk/Products/MK3190.html?ad_position=1o3&source=adwords&ad_id=45425533757&placement=&kw=&network=g&matchtype=&ad_type=pla&product_id=MK3190&product_partition_id=174047728387&test=finalurl_v2&gclid=Cj0KEQiAtqHEBRCNrdC6rYq9_oYBEiQAejvRl9q0kfiwts0prSeS5t2X-n0PtC0iK-Ov9BnaU6ItxO0aAiM38P8HAQ

 

I expect you can also get them with a white cord.

 

 

 

[Temp]

Just remembered that there are some switches designed to be hidden behind tiles...

http://www.taptilecontrols.com/

http://www.sensor.co.uk/switches/bathroom_switch/

 

You would need to check if these are available with momentary/retractable outputs.

 

[Jeremy Harris]

47 minutes ago, dogman said:

Have you looked at a roof mounted pir to switch it to boost when you enter. Most work on a N/C or N/O low voltage circut

 

 

These work well, with one slight reservation.  I fitted one around ten years ago in the ceiling of the bathroom of our old house, to switch the extractor fan on.  I had a standard switched double gang13A socket in the loft, immediately above, so it was a doddle to fit the PIR sensor in the bathroom ceiling and wire it to the SELV transformer that powered the fan over the shower, at the other end of the bathroom.  I disabled the PIR light sensor (it was one with a time delay but no light sensitivity adjustment by putting a bit of black paint over the LDR - safe and easy to do, and hidden when the thing is reassembled).  This made it operate day or night, whenever anyone enters the bathroom, and has been very effective at keeping the bathroom free of condensation.

 

The slight reservation is that it puts the fan on in the middle of the night, if someone pays the bathroom a nocturnal visit, and the fan then stays on for the duration of the timer.  As it happens, with both the bathroom door and our bedroom door closed we can't really hear the fan, but with MVHR you may well hear a bit of noise from the bedroom supply terminal if it's on full boost in the middle of the night.

 

Our MVHR is virtually silent normally, and there's no audible sound from the bedroom vents when it's running in normal ventilation mode, but there is a tiny bit of noise from them when it's on full boost.  Whether or not that's enough to be a nuisance I don't yet know.

 

Perhaps a PIR in series with an external time switch might do the job?  That could be set so that the PIR isn't powered up at night, so can't operate the boost.

Edited January 25, 2017 by JSHarris

[joe90]

Good point Jeremy, perhaps in mine I will use the RH sensor to clear condensation and an emergency " curry" button in case of air pollution if needed.?

[dogman]

I have  ventaxia pir controllers that have a built in timer. As @JSHarris We do have a slight increase in noise but our controller has 2 aux inputs so i have one set at about half speed when entering bathrooms and one for boost that is full speed via boost switch

 

[JamieM]

3 hours ago, ProDave said:

Also do you jut want a boost on / off switch or a timer?

Yes, it's a timer so click it and it stays on for a set amount of time (say 15mins)

 

3 hours ago, joe90 said:

 

I had not thought of a boost button for mine but thought the humidistat within the unit would suffice?

 

Boost is too get rid of nasty smells. Probably do no harm to turn it on before a shower too as it may take a few minutes for the automatic humidistat to come on)

[Fallingditch]

So that's a slightly different use case - manually operated switch which works in parallel with a humidistat.

 

I am not an electrcian and I am certainly not familiar regulations - but there is a £50 product from Danlers: "exterior time lag switch" EXTLSW. IP 66 rated and they state "also suitable for damp areas indoors'. Adjustable 2-20 minutes. Even comes with an orange button. A bit industrial looking though.