Bathroom fan heater


Postby ithomas860 » Mon Feb 07, 2011 10:07 am

Hi Folks

I have an unheated shower room that I want to install a fan heater in. Can I run a feed for this from the ceiling mounted power switch for the electric shower? The shower is 8KW fed from a 32A RCB. The rating of the Fan heater is 1000/2000W. If it is possible/recommended what size cable should I use? this would be in trunking running along ceiling.

If this is not possible any suggested solutions?

Thanks

Ian
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Postby ericmark » Tue Feb 08, 2011 3:34 am

8kw at 230v = 34.8A clearly you can’t power an electric heater at the same time as the shower.
Second problem is Part P building regulations and cost of registering work with LABC.
If the house has water central heating this would be the best way forward.
An 8kw shower is more like drizzle than a shower and if you do have hot water central heating then shower feed by water heated by the central heating must be best way forward.
With combi boilers direct feed but with storage tanks for hot water the power shower is the way forward.
Years ago we had some really dangerous heaters used in bathrooms. However today regulations will only allow us to use a heater designed for use in a bathroom. The normal method is the towel rail. Under floor heating is also used but again has to be type allowed in bathrooms.
The problem with a fan heater is often we need ventilation and opening a window with a fan blowing the air around can make the room too cold so maybe not best option.
At 2kw one should not connect direct to ring main. But lower wattages for example the 850W load of a towel rail or tubular heater could be connected to the ring main.
The switches to switch it on and off if in the bathroom also will need to be of a type designed for use in the bathroom.
And of course now everything in a Bathroom needs RCD protection.
Because DIY is so expensive with LABC charges I would get an electrician to look at the problem and give a quote for his remedy. No point in doing loads of work if in the end it will work out cheaper to get a registered electrician to do the work for you.
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Postby ithomas860 » Tue Feb 08, 2011 8:53 am

Thanks for the reply ericsmark. Sadly the house does not have a combi boiler so the power shower option is definitely out. The type of fan heater I was considering was rated for installation in a bathroom but if the shower circuit wont take the load, thats the end of that. I cant rip the house apart to get it a dedicated supply up to the shower room. What are your views on changing the rcd to a higher rating ? If the cable is suitable of course. Ultimately I will be calling in a pro for the job but just want to make sure I know all the options available to me.

I like the towel rail idea fed from the ring main (installed as per regs of course) so will have a look at those as well.

Thanks again
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Postby lazza » Thu Feb 10, 2011 11:00 pm

you still cannot run heater off shower even if you change RCD.
Have you got central heating in adjacent rooms ? there may be pipes running under or near shower room you could put a towel rad in to work off the C/H
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Postby ericmark » Sat Feb 12, 2011 3:07 am

Cable sizes jump from 6mm to 10mm then 16mm and the 6mm cable is often rated at 32A hence why so many showers are just 8kW so they can run off a 6mm cable.

Likely therefore even if you wanted to that you would be unable to up-rate the MCB or RCBO to a larger unit.

The RCB does not limit current it is only to protect for earth leakage and is selected to be able to switch a specified current for example 63A, 80A or 100A but does not trip when there is an over current. It may however burn out or go on fire.

The MCB does limit current and has two current limiting parts. The thermal bit works as it says on the device i.e. a B32 will trip at 32A but it will take some time for it to trip. The B in front of the number shows it will trip at 5 times the 32A with the magnetic part so at 160A it will trip within 0.1 seconds. A C type is 10 times and a D type is 20 times. It is because it needs such a high current to trip with a short circuit that electricians need to measure the earth loop impedance to ensure with a short circuit the device will trip with the magnetic part within the 0.1 seconds.

The RCBO combines the MCB and RCD together in one unit.

Most showers even if feed with a heavy cable 10mm or 16mm rely on the MCB in the consumer unit to disconnect them should there be a fault so to replace the B32 MCB with a larger one even if the cable permitted it would mean the shower is not protected correctly so the cable would have to feed a local sub main and a second mini consumer unit before it's supply could be split to feed two items.

So in real terms using the shower cable is not going to be possible.
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