Moving storage heaters

Postby Shanklinman » Wed Apr 14, 2010 7:52 pm

Last year we moved to this flat which is heated by 3 storage heaters. A 3.4 kw in the living/dining room, a 3.4 kw in the hall, and a 2.55 kw in a bedroom. We suffered very bad condensation this winter and suspect the cause is due to these being badly positioned as they are almost next to each other in the centre of the flat. Only doors separate them.

What I would like to do myself is to move the 2.5 kw from the bedroom to the living room, but in a different position, and dispose of the very old 3.4 kw. I want to extend the wiring from the existing point along the living room wall, enclosed in self adhesive plastic trunking and add a new switch. Hopefully that is straight forward.

Additionally, I would like to dispose of the 3.4 kw in the hall and again using the original wall switch, run an extention in the same way to the dining area, (off the lounge), and fit a new 1.7 kw to that end of the room. However, from this same hall switch I would also like to run a second separate cable along the hall wall to a better location and fit another 1.7 kw heater (total 3.4 kw). I have read somewhere this is acceptable under the wiring regulations, but other people insist it is one heater to each switch.

With the 3rd remaining point in the bedroom, I would like to do the same and fit a new 1.7 storage heater under the window, plus a second one 1.7 in the next bedroom.

I would really like to know if this plan will meet the wiring regulations, and whether I can do it, or must it be done by an electrician.

Many thanks in advance for any advice you can give.

Posts: 3
Joined: Wed Apr 14, 2010 6:34 pm


Simply Build It

Postby ericmark » Thu Apr 15, 2010 8:46 pm

When a storage heater switches on it take max current until pre-set temp is reached which means there is no diversity.

With 3.4Kw you are looking at 14.78 amp i.e. over 13 amp so only way to fuse or protect is in the consumer unit which will likely have 16 amp MCB or fuse and radials to each heater so likely you can't put two heaters on one supply.

Around 16A can do loads of damage and even fire if there are any poor connections although you could join cables it would need to be very good job.

Likely a cooker outlet would give the connection JB required but again often no RCD and if cables are buried it would now need a RCD again over 3kw so the RCD FCU would not work.

With that current the ELI becomes very important and before extending cables you need to check what it is already and if you can extend without exceeding the permitted loop resistance.

If for example a heater is supplied with a 1.5mm cable at approx 0.029 ohms per meter with a 16D MCB allowing 0.72 ohms of which 0.35 ohms are used by supply that limits one to 13 meters. This could be easy exceeded. Unlikely a 16D MCB would be used and also unlikely 1.5mm cable but you can't guess it needs to be measured and for this reason I would suggest this is not a DIY job.

Since you are considering renewing the heaters over 3Kw very likely you can protect with a RCD FCU where old supply ends and then extend and it is unlikely that this would not comply but "Unlikely" is not really good enough and to be sure you will need £750 worth of test gear.
Posts: 1374
Joined: Fri Oct 02, 2009 8:49 pm
Location: Mold, North Wales.

Postby Shanklinman » Sat Apr 17, 2010 6:58 am

Thank you ericmark for your very helpful reply.

I have checked and the 4 radials come from 2 separate fuse boxes and it is 2.5mm cabling. Each has 20 amp glass cartridge fuses. I think the first double fuse box was original, as the radials are buried in the internal walls. (Brick and plaster). The other pair was presumably added later as they are surface mounted.

You have made me realise what seemed a simple job, of not increasing the load on each radial, is not straight-forward at all. As we can't cope with the winter condensation, we will have to try and get a local electrician in to deal with the problems you have kindly high-lighted for me.

Out of interest, I wasn't certain whether your answer is saying 2 heaters connected to one radial can meet the wiring regs. or if it was the technical reasons you gave that precluded it.

Many thanks again for your advice

Posts: 3
Joined: Wed Apr 14, 2010 6:34 pm

Postby ericmark » Sat Apr 17, 2010 11:42 am

Correctly configured one could run many heaters off one radial. The cable would need to be big enough and the heaters would need local fusing.

The latter is the problem as in the UK we can get fused connection units "FCU" for up to 13A without a problem but over 13A their size becomes a problem as they are designed for commercial not domestic.

So under 3KW you could pair them up but then we look at cable size. 2.5mm cable does not have a single amp rating but it varies according to the temperature the cable can handle and the way it is cooled.

Clipped direct to a cold stone wall and with cable able to run at 90 degs then one could be looking at 33A however with 70 degs cable running through a stud wall with insulation in wall the rating could be 13.5A for same size cable.

Flex has a current ratting as rules for use of flex say it must be visible for whole of run so is always in free air. So 2.5mm flex is 25A cable on single phase but that does not apply to fixed cables.

Personally I would think position of heaters should not effect condensation. The real problem is air changes. In old houses with open fires the fire would ensure loads of air (Drafts) was drawn into the room heated and disposed of up the chimney. The introduction of central heating not only heated all rooms but stopped the air flow. To an extent this is good as no drafts but it also means where plants, and people are in the rooms we get loads of moisture which will precipitate onto any cold surface. Single glazing with small holes at the bottom leading outside could remove this water but then we started to double glaze as well.

So today we have Three methods in general use.
1) Fit vents and increase air changes.
2) Install a special cold surface to collect the water
3) Absorb the moisture in special transportable material then expel it again.
The first can use heat exchanges so as not to cost too much to re-heat new air but a Vent-Axia 3-Room Heat Recovery unit for screwfix costs £700 however it is likely to be best option.
The second two are the two methods used by dehumidifiers.

In my house I have a air pump which takes the warm air from the kitchen and then warms it even more to absorb even more water then blows it out of the house through a pipe. More technician description would be tumble dryer. Seems odd I know but most houses have either fans in their bathrooms or kitchens which do ensure some air changes.

The other type of tumble drier which puts water into a bucket works in same way as dehumidifier and again would remove water not only from cloths but also the room without putting used air outside so are dearer to run in summer but cheaper in winter although this is not shown in economy data.

What ever method you use it will cost. Of course one must also look at water entering from outside. My washing machine developed a drip. About one every 5 minutes. This water then went under my floor. Until it built up enough so walking on the laminate floor caused water to come up through joins as we walked on the floor we were unaware there was anything wrong. The same happened with our shower. Leak between controller and shower head was allowing water to build up between the stud walls.

Until my daughter came home we were not using the shower long enough for the water not to be evaporated again and we noted damp on window sill but did not realise this was due to a leak. With daughter taking more showers the water started to build up until the ceiling could not hold it any more and it bellowed and cracked depositing the water on carpet below.

New ceiling and carpet later with leak cured we realise this was why the bed room was damp. At least now no longer a problem. Even though there was an office between bathroom and bedroom. Brick ties upside down can also cause this type of problem in that case cavity wall insulation can often cure it as it seals the walls.

Of course I could be completely wrong but I would be looking else where first.
Posts: 1374
Joined: Fri Oct 02, 2009 8:49 pm
Location: Mold, North Wales.

Postby Shanklinman » Sun Apr 18, 2010 1:26 pm

Many thanks again for reply, and I do appreciate your comments about the condensation problems.

The reason I thought I should deal with the storage heaters first, was because the two 3.4 kw heaters are extremely old, and as I mentioned before, are located in the centre of the flat, a long way from the external walls. Our lounge faces south east, and the dining room area faces north west. Similarly, the 2 bedrooms face south east. As a result, the external walls being very cold this winter, condensation seemed almost permanent on both sides of the buildings external windows and walls.

I reasoned that lack of proper ventilation would be the primary cause, but with more heaters, more strategically placed against the external walls where the condensation was the worst, would considerably curtail it, but not necessarily cure it. Also, being in a block of flats, I cannot make changes to the structure that will improve the ventilation. Normally, this is a very mild area in winter time, but this winter was exceptional, and opening windows to reduce condensation wasn't possible as often as would be normal. I do think with all the heating being in the centre of the flat made things much worse.

I will take professional advice following your good advice, and your additional comments on condensation I will keep in mind. I do hope the changes to the heating first will make the flat a great deal more comfortable in the first instance, and then I will hopefully be able to do whatever else is needed to eradicate the condensation remaining.
Posts: 3
Joined: Wed Apr 14, 2010 6:34 pm

Postby ericmark » Sun Apr 18, 2010 10:06 pm

Never had a problem in my flat. But likely it was because it was in Hong Kong. Electric bills in summer were huge. Winter was OK though. Sorry no real help that I can offer.
Posts: 1374
Joined: Fri Oct 02, 2009 8:49 pm
Location: Mold, North Wales.

Display posts from previous
Sort by
Order by


  • Related Topics