I had four Unidare night store heaters fitted in my home 4 years ago. For the first years they worked very well. No problems.
This winter a fine black dust has emanated from them and coated every surface in my home. Walls, floors ceilings, soft furnishings, cupboards etc. every surface is black. I have tried to clean the black off the walls and it is impossible to clean. The supplier fitted new bricks two weeks ago, but this has made no diffeence and the black dust continues to emanate from the heaters. The supplier is going to redecorate and supply new heaters, but I want to know the cause. Is the black dust toxic? I have been breathing it in for weeks. Will it happen again when the new heaters are fitted?

J. M., February 2010

Its from the heaters!! I have two Dimplex heaters, they are vile. Soot showing actually at the vents at the side. I do not burn candles, use air fresheners, I open windows, but my whole flat is covered in black dust...carpets, curtains, everythings. It IS the heaters. They are dangerous to health, I have suffered immensely this year with chest problems because they have been on for far longer than usual due to the extreme cold. No gas in the apartments unfortunately so not a lot of choice, but these things are dangerous so don't try to say they aren't! I am now being tested for asthma!!!

Ann Deaves, April 2013

I found this... (it may be significant - or perhaps not)

There is a black "soot" coming from my radiant heater
it goes up the walls above where the heaters are installed and on the windowes and curtains, and this "black soot" is not easy to clean or wash out of fabrics. There were new heaters when i moved into my condo 4 years ago and i am constantly repainting my walls because i cannot wash or remove this "black soot". What would cause thsi broblem

Black soot appearing above and around electric baseboard heaters is caused by burnt hydrocarbons in the air.
The Heating element draws the cool room air from the bottom and over the element. Any excess hydrocarbons in the air become burned and are deposited on the surrounding surfaces from the warm heated air flowing up out of the heater.

The Heater is not the cause of these hydrocarbons. They come from the home / enviornment.

Some cause.
Smoking, burning Candles releases waxy hydrocarbons, carpet cleaning solutions, spray type air fresheners.

Black waxy sooty deposits are usually from burning candles.

http://www.fixya.com/support/t1535561-black_soot_coming_from_radiant_heater

Peccavi, February 2010