Sizing electric boiler

[silver50]

Is the point in using an electric boiler to heat water as well as it providing central heating so as water will get heated when the central heating is on, therefore surely giving some kind of saving over having the two completely separate. Of course it would only work like this when the two are asked to heat at the same time?

I need to choose sizes and don't feel oversizing the boiler is necessarily a good idea. My central heating requirement is going to be around only 3.5Kw worth. Going for a 6kw boiler seems then like it might be fine, stepping up to a 9kw one for example, seems like probably too big and maybe costlier to run.

Input appreciated. It'll just be getting used on a single rate electricity tariff. Thanks

 

[Ted777]

Do you have a separate hot water tank?

 

[flameport]

My central heating requirement is going to be around only 3.5Kw worth.

If it's that low, why bother with a wet central heating system at all?

 

[silver50]

Going to be a new unvented cylinder installed.

Indeed been a bit tricky to decide whether to just go for some electric radiators but I like the idea of still having "central heating"

I'm going to delete bathroom wet radiator due to install issues (not wanting to rip up floor- just going to have a 500w towel rail electric element and I could do without a hall radiator. just a one bedroom flat. Two radiators needed for kitchen and living area 50/50 spaces and one for a small bedroom

 

[PullerGas]

Is the point in using an electric boiler to heat water as well as it providing central heating so as water will get heated when the central heating is on, therefore surely giving some kind of saving over having the two completely separate. Of course it would only work like this when the two are asked to heat at the same time?

I need to choose sizes and don't feel oversizing the boiler is necessarily a good idea. My central heating requirement is going to be around only 3.5Kw worth. Going for a 6kw boiler seems then like it might be fine, stepping up to a 9kw one for example, seems like probably too big and maybe costlier to run.

Input appreciated. It'll just be getting used on a single rate electricity tariff. Thanks

Perhaps a 'storage' type electric boiler would be best silver50. The tariff is critical really.
http://www.mcdonald-engineers.com/products/Electric-wet-central-heating-system

 

[Ted777]

I would get a wet central heating if I didn't have access to gas. I've had storage heaters in the past and I hated them, trying to second guess if I'm going to be hot or cold tomorrow was a pain.

 

[silver50]

Thanks for that. Never seen those before. I can see your thinking, it really does heat one lot of water but you'd pretty much need constant very hot water at the ready. I wonder how much they are..

The electric flow boiler is of course good to provide instant CH, and if used to heat water, it can do it quite quickly. It's picturing how well it flows the CH and heats water at the same time i'm not sure about. People do run the flow boiler separate from their water heating (immersion in cylinder) but it appears to be best to have the flow boiler heating the water if you were starting afresh with new cylinder too.

I'm trying to fully understand the benefit in the boiler heating the water too (and from there gauge size of boiler). Perhaps it is only a small advantage really, this being if both water and CH on at same time.

 

[PullerGas]

Most of the storage type electric boilers heat the tank on a cheap rate tariff, depending on supplier it can be very economic. Scottish Power did have a great tariff for storage Combi electric boilers.

It depends also if you are letting the property & you're not overly concerned about running costs.
The same goes for installation costs; a wee 'flow through' type boiler & E7 cylinder will be cheapest to install.

 

[silver50]

Flat is just for renting but quite upmarket wee place, so that's one of the reasons for wanting wet central heating.

I ended up with the flow boiler and a direct UV cylinder elsewhere (so both separate) but my electrician always felt it would've been better to have had the flow boiler heating the water too. He seems to be right but I'm trying to see what the advantage really is?

Will just be on a single tariff

 

[PullerGas]

Flat is just for renting but quite upmarket wee place, so that's one of the reasons for wanting wet central heating.

I ended up with the flow boiler and a direct UV cylinder elsewhere (so both separate) but my electrician always felt it would've been better to have had the flow boiler heating the water too. He seems to be right but I'm trying to see what the advantage really is?

Will just be on a single tariff

If it's a 'selling' feature, why not look into getting a dual/cheaper tariff. It's amazing how people like using cheap tariff for washing machines etc in a family home.

I'd say an E7 type direct cylinder would be cheaper to install & run than having an indirect cylinder from a flow through boiler. Plus you avoid zone valves etc.

 

[silver50]

It's really really tricky to decide exactly what's best. My father did quite a few sums on it before we fitted the above leccy system elsewhere and felt a good general tariff just about equalled off peak because the peak times were so much more. Of course actual storage heaters will be a bit more cost effective on off peak

This is why I ideally want to just install something practical but not get too big a boiler so as the cost isn't crazy. It shoudn't be too bad in such a small flat I hope

 

[flameport]

I'm trying to fully understand the benefit in the boiler heating the water to

If it's a larger boiler, the cylinder can be heated more quickly - an immersion is usually only 3kW, so with say a 9kW boiler it would be much quicker to heat the water.

I've had storage heaters in the past and I hated them,

Other types of electric heater are available.

 

[silver50]

Yes. I see the advantages of using a bigger boiler, but am a bit worried it's power consumption would end up higher if you did choose 9 over 6.

Should it not actually be any more costly in the end ?

 

[stem]

Electricity is 100% efficient. All of the energy that goes in, also comes out as heat. There are no flue losses.

As boilers are internally regulated, the temperature of the water leaving the boiler is kept constant by controlling the heating elements accordingly. So to illustrate, if a property required 3kWh of heat, then a 6kW boiler will be operating for 50% of the time to provide that. In the same situation, a 9kW boiler will only operate for 33.3% of the time, so despite having a larger consumption when it is running, it will be running for less time, and the electricity consumed will be the same.

During the summer, using an electric boiler would use more energy than heating the hot water directly with an immersion heater. This is because when the cylinder is up to temperature and the system shuts down, the boiler and associated pipework will still be full of hot water. This heat will then be lost to the atmosphere and wasted. However, it won't be very much, and it wouldn't be a problem in the winter as it would go towards heating the property anyway.

Unfortunately electricity costs about 5 times the cost of mains gas, so isn't cost effective for most wet systems which tend to be 10kW plus, but in this case as yours is so tiny it would be more viable.

 

[PullerGas]

Not many places in & around Edinburger don't have Nat Gas.
Believe me I know, I regularly work in the shyte hole of a city.