Adding isolator switch to a single room heat exchanger fan

[Fishwalker]

Hi,

We had a new single room heat exchanger fan installed by our electrician last weekend but it went faulty the same night. We think the pull cord switch that takes it from trickle to boost somehow failed as it turned to boost from trickle by itself and won't switch back. It is a basic pull cord only. No humidistat or timer.

Our Sparky didn't install an isolator switch though, even though the manual says the following:

"The Fan should be provided with a local isolator switch capable of disconnecting all poles, having a contact separation of at least 3mm. Ensure that the mains supply (Voltage, Frequency, and Phase) complies with the rating label."

My sparky is away now for a week and we are stuck with our broken fan turned on constant boost mode, only able to be turned off at the fuse box. It is on the 6amp ceiling light circuit but is not timed so is on without the light. The supplier has today sent a replacement fan so we could change it over ourselves.

My other half says he can confidently do this and install an isolator switch next to the fan. It is located in our kitchen at least 2ft/600mm above the sink in an old vent hole. Is he allowed to do this himself or does it need to be a qualified electrician?

Also does anyone know whether when you hold your hand under a heat exchanger fan, whether it should feel cold near the wall, directly under it?
I thought it was supposed to be bringing warmish air back into the kitchen but not sure how it's supposed to work as the manual and website doesn't say what is normal and what is not.

[url]http://www.vent-axia.com/product/lo-carbon-tempra-selv-t.html [/url]

 

[ericmark]

Unfortunately the link does not works seems the Vent-Axia site is down. I am assuming your talking about a heat recovery unit?

There is no requirement to notify a replacement but clearly person doing the work must have the skill.

314.1 Every installation shall be divided into circuits, as necessary, to:
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit.

Not to fit an isolator so that you will lose lighting should it become faulty clearly does not comply. Even with an isolator it could be claimed it did not comply but one has to use a little common sense.

Since a heat recovery unit both pumps air in and out it should not cause a depression and there should be no drafts. The whole idea is that open flue fires can be safely used with a heat recovery unit where with a simple extractor it could draw flue gasses into the room.

Clearly these units need so ducting removing air from cooker hood and replacing it to opposite side of the room. Also the outside vents needs some distance between them.

Some thing seems wrong. You talk about only one hole there must be two one in and one out.

May be it's not a heat recovery unit but an air conditioner?

 

[ericmark]

Interesting web site now works the instructions state

When the Fan is used to remove air from a room containing a fuel-burning appliance,
precautions must be taken to avoid back-flow of gases into the room from the open flue of gas or other appliance. Ensure that the air replacement is adequate for both the fan and the fuel-burning appliance.

It would seem unlike all other heat recovery units I have seen it has a single fan which blows air out of the room and relies on the rooms being sealed enough to drag air back into the room through the heat exchanger rather than any other point.

The unit

blows air from the front of the unit horizontally but allows return air to enter from below and exit from below the unit.

This is the first I have seen which does no require a large box and I am impressed. It would seem adding an isolator should be simple.

There are some mistakes in the fitting instructions SELV = separated extra low voltage not safety extra low voltage for example. Use of 24 volt seems a little odd as where SELV is required it often stipulates 12 volt.

But the main problem is the room needs to be sealed for the unit with a single fan to work. Simply leaving the door open to rest of house could mean replacement air does not enter through the heat exchanger.

Having multi units would work as you would ensure the house is always at a lower pressure than outside.

The question is of course are there any open flues? When I first read open flue I thought of the open fire but this is not what "Open Flue" means. An open flue is where the combustion air is taken from inside the house. In other words anything which is not a balanced flue is an open flue.

The gas cooker has no flue so this is the exception.

Some appliances may help the process. A ducted tumble drier will also cause a depression in the house so draw in more air through the heat exchanger as will any other extractor fan in the house.

But my house the internal doors are simply not well enough fitted and I also have vents in the velux windows which would mean this unit in my house would not works very well.

 

[Fishwalker]

Hmmm the Vent Axia website was down last night I think. I couldn't get on either. The page again is http://www.vent-axia.com/range/lo-carbon-tempra.html

It has a little video explaining how the heat recovery process works.

Our house is old and drafty (1904 terrace) We have an ill fitting cat flap for one but the room adjoining the kitchen is pretty air tight e.g. double glazed with a chimney balloon up the fairly large period chimney.

The switch will go after the light fitting in the 6amp circuit so the light is controlled separately. It is just that currently you have to turn the whole downstairs circuit off at the fuse box to stop the fan with the isolator switch.

But check this out!

We have the replacement fan from Amazon that came really quick and we haven't uninstalled the faulty one yet. But today, I turned on the lights at the fuse box and the fan came on boost as per and for fun I thought I'd pull the cord and low and behold... it went to trickle mode!!!!!! It is still on trickle now! So I am wondering if we should keep it now or swap it for the replacement new one we have. It seems a bit rubbish that it is has been faulty for 5 days with the pul cord doing nothing though so I think it's best to swap it. It just doesn't instill faith in the pull cord system for the future but I'll have to see I guess.

 

[Fishwalker]

Oh, by the way, we have no gas appliances in our house. Our cooker is fully electric and the gas pipe capped off, as is the fire in the next room. ONly the boiler is gas and that's upstairs in the bathroom with its own vents.