Central heating system choice

[polycage]

Just having an extension built on my 3-bed semi and will replace the boiler with a new one. A friend has suggested that I get a dedicated water heater and a seperate 30000 btu boiler to use just for the heating. The heating boiler would be left on all the time with an electronic thermostat lowering the temp at night and during the daytime. He reckons this will be cheaper as the boiler will never really be used to heat the whole house from "cold", hence only 30000 btu boiler.

Anyone have any thoughts on this?

 

[doitall]

Nice

 

[polycage]

Do you think it will be cheaper to run? The price compared to a good combi boiler doesn't seem too much more. Labour will be more but that's no big deal.

 

[doitall]

NO I don't, If he means what I think

And don't have a combi can either.

Get yourself a nice unvented cylinder with immersion heater backup, and a condensing system boiler.

 

[polycage]

I've got a fan flu conventionbal system now but need to remove the cylinder out of the bathroom to fit a shower. Why would the original idea be cost more to run? My mate says the heating boiler would never be working above 30000 btu.

 

[Panjandrum]

Would this be any better than a single boiler system with room and cylinder stats and separately timed CH and HW?

 

[doitall]

First what does your mate call a dedicated water heater.

Could be a kettle, or an electric shower or even a second boiler.

And what authority does her base his opinion on.

 

[polycage]

He's recommending a seperate boiler just for water. He told me to look at the Baxi/Maine range. He used to work for Satchwell as an engineer all over the world and found this system to be more efficient. Just seems a bit odd to me. Not that I'm educated in this kind of stuff.

 

[doitall]

In a commercial estabishment where hot water takes priority, but in a domestic house the mans talking out his hat

Ok so modern boilers are as reliable as a skoda with no wheels and a back up hot water supply is a very good investment.

 

[Panjandrum]

Cheaper? Does he mean cheaper to install or cheaper to run?
There's an intuition that not ever having to heat from cold saves fuel costs. But that doesn't square with the law that says that heat loss depends on the temperature difference - so you loose more £s for longer if you keep the heat going, even at a lower temperature.
On the other hand, if you have a huge installation, the capital costs of a system capable of bringing the whole ten floors from overnight cold to satisfactory working temperature might well work out to be less economic than a less-powerful system keeping the temperature going all night. Bring on an economist and an accountant.

 

[ChrisR]

He reckons this will be cheaper as the boiler will never really be used to heat the whole house from "cold",

Drivel.
You only allow 10 - 20% extra to the steady-state building requirements to allow for heating up. 30k is likely to be inadequate for an extended 3 bed semi in very cold weather. These days we plan for -2 or colder.

It isn't cheaper to install 2 boilers than one is it!!!

If a modern boiler needs to produce less heat than its full capabilities it turns itself down and burns less gas. The efficiency difference between than and having a smaller boiler running flat out aren't worth talking about.

I agree with Panjandrum.

If you want to go for a combi for space reasons, having an electric shower somewhere isn't a bad idea.

 

[ArtfulBodger]

I think he means a water heater like a Main Mersey rather than a combi for the hot water side. These have always struck me as very simple and quite good fwiw

 

[polycage]

Sounds a bit clearer now. He did have a huge house so it may have worked in his.

Another reason for the seperate water heater as opposed to a combi was the pressure drop problem, ie, whilst having a shower and someone else turns on a tap downstairs or similar. How can I combat this with a combi setup? I had a Valiant a few years ago and it was a nightmare. Are modern boilers better at this?

Thanks for all your help guys. Your opinions are valued.

 

[kevplumb]

if you have a water heater you will get the same prob

only way to stop that is a cylinder

vented/unvented

 

[polycage]

Are there combis that are better then others when it comes to pressure loss? I really need the space that the cylinder is taking.