Do I need new cable for 12kw???

[Alfa1steve]

Hi all,

I am thinking about buying a thema flow combi boiler to replace my immersion heater and night storage heaters.

The boiler will be housed where the current water tank is and it currently has 2 immersion heaters rated at 3 kw each one on economy 7 the other as a booster.

The information from the combi is:

Electrical supply off peak

Boiler power rating 12kw
Rated voltage single phase 240v
Rated current is 52 a

24 hr normal domestic supply

Power consuption of controls 190 watts
Rated voltage single phase 240v
Rated current is 3 a

If any one can be of any help at all this would be appreciated

 

[RF Lighting]

Yes definatley.

You will need a much larger cable installing, and possibly some upgrading or replacement work to your fusebox, and you might even need your main incomming supply to your property increasing.

 

[flameport]

It will require a new circuit.

Before you make an expensive error:
how many storage heaters do you have?
what size are the existing storage heaters?
do these storage heaters provide enough heat for your home?

 

[Alfa1steve]

Thanks for the reply

To answer the first post how would I know that my mains power into the house needs increasing???

To answer the second post I have 2 storage heaters each rated at 3kw, yes they heat the flat fine but sick of guessing what the weather will be like the next day and terrible water pressure and I can't add a mixer shower. Why would installing one of these be an expensive error?

 

[ericmark]

I am sure you can read the instructions the same as me and see it needs a 52A supply which should have a 63A isolator and have at least a 16mm feed cable for the off peak supply and is only for houses with the full 100A DNO fuse fitted.

So with such a large supply it will likely be feed directly from a DNO supply and will not be feed from the standard consumer unit. Only the 3A control supply will come from the consumer unit.

With a 52A supply the installer will have to carefully consider the route and if there is a problem with the cable temperature then he may use even thicker cable.

How it is connected will depend on tariff but quickly looking at the instructions is does not show a separate supply for on peak boost and it calls the off peak supply "Interrupted off peak supply" so I can't see any method to get a boost during peak times.

238kgs of water should hold a fair bit of energy around 25kwh and that is of course for the 14 hours when you have no power going in so average of 4kw always available. (Longest off time 6 hours)

But this sort of job is not DIY. It will be installed by I would hope people who know what they are doing. So really don't understand the question?

 

[riveralt]

Thanks for the reply

To answer the first post how would I know that my mains power into the house needs increasing???

For a boiler this size the manufacturers usually insist on the service fuse of 100Amps per single phase. You need to check what the manufacturers recommend and what size service fuse you have.

This should have be picked up by the installers when they came to give you an estimate.

 

[RF Lighting]

Despite this being a domestic job, you really need to invest in the services of a commercial electrician, who will be more familiar with working with the heavier duty switch gear and large supply / cable required for this boiler.

 

[Alfa1steve]

Hi guys
Please don't think I would attempt to install this myself, I'm an aircraft engineer not a spark lol

The only reason I am asking these questions is to try and find out how much hassle this is going to be if you know what I mean

 

[ericmark]

Thanks for the reply

To answer the first post how would I know that my mains power into the house needs increasing???

To answer the second post I have 2 storage heaters each rated at 3kw, yes they heat the flat fine but sick of guessing what the weather will be like the next day and terrible water pressure and I can't add a mixer shower. Why would installing one of these be an expensive error?

Sorry answered while I was writing reply. The size is ample to replace the original two radiators and yes I agree the wet system does give more control. The considerations are first of course the weight 405kg is not light and the place it is installed needs to be able to support that weight. Second is tariff it is designed for Economy 10 for wet systems which has a number of on times unlike the old Economy 7 system. And third you need a 100A supply to flat. The flat could be feed with anything from 60A to 100A and the only people who can tell you what the supply is are the suppliers (DNO) this is not the same as billing agent.

As to what cable needs installing that would depend on where the heater is. (Not sure why we call them boilers as we don't want them to boil water?) The cable will get warm. And so it must me routed where it can cool. But we are obliged to follow manufactures instructions so it will be at least 16 mm sq csa. Some houses only have that size cable feeding whole house. Since you already have electric heating likely the supply will be big enough but worth giving the DNO a ring to check.

 

[flameport]

This type of heating can easily be a very expensive mistake, as they are only suitable for very small, extremely well insulated properties.

In your case, if the 2 storage heaters are enough, then the heat output from this proposed system is probably sufficient. However you will need to get the E10 tariff or equivalent, which provides several heating periods throughout the day (10 hours in total) rather than E7 which is only overnight for 7 hours.

The manufacturers state that the largest size of 330 litres can store 38kWh of energy.
Your existing storage heaters can store about 42 kWh (2 x 3kw x 7 hours to fully charge). Then there is the extra for your existing hot water system.

Other things you need to know about this type of heating appliance:
- Despite some manufacturers claiming they are maintenance free and last for ever, they do break in all kinds of ways.
- When they go wrong, they are usually very expensive to repair.
- When it breaks, you have NO heating or hot water at all.
- They are not cheap to run, since all electric heating is far more expensive than other fuels.

 

[Taylortwocities]

You do also realise that the night storage rads will have to go and radiators and associated pipework installed?

You will need two immersion feeds and the 50+amp main feed.

I have installed a couple of these systems (Electromax) and they were very expensive for the customer to run. The real cost comes if you want to be warm outside the cheap rate periods. Other issues are with timing of use of immersions etc etc to be in sync with the off peak times.