Is it worth over speccing a combi?

[sbrewster2]

I have a 2 bed flat (1 bathroom) with 5 radiators.

Washing machine and dishwasher are cold feed only, so the only real DHW requirements are for the bathroom (and the kitchen sink, but that doesn't get used much!).

Is it worth specifying something like a Worcester Bosch Greenstar 40 HE Plus or Baxi 133 HE Plus just to get a good shower and a quicker fill on the bath?

Is this just overkill? Is there likely be other limiting factors such as mains pressure/flow, internal pipework etc?

Can I just assume that the higher the DHW flow of the boiler then better shower I'll get?

I don't mind spending extra for a really high ouput boiler if it's going to give me a really good flow at the shower/bath.

Any help greatly appreciated.

 

[Dukie1977]

Check your incoming flow rate from the mains first, you wont get a better flow rate than this from your boiler.

Rich

 

[Agile]

For most people a 30 kW boiler is totally adequate for normal showers.

A higher power boiler will fill a bath quicker or allow a little water to be used in the kitchen.

Be aware that any cold water useage will have to be included in the incoming flow rate requirement. The supply pipe might have to be upgraded, thats ofter about £1200.

Your CORGI installer should be able to advise you on all these topics and measure the flow rate into the property.

Tony

 

[corgiman]

well put Tony

if you must have a combi gett the biggest meanest get that you can afford

 

[sbrewster2]

Thanks for the advice.

Unfortunately yes, I must have a combi (I'm short on space as it is).

If I get the biggest meanest combi I can afford, will it automatically regulate itself with regards to the CH? Someone on the Screwfix Plumbing forum warned that the boiler would be continually switching on/off during the night when running the CH.

 

[JohnD]

You can have oversized rads as well (with TRVs of course), this has the advantage that the rooms will heat up faster from cold, and also gives the boiler more water content to work on so avoiding short on/off cycles.

In my own house, I like to swap small singles with big doubles when redecorating, it's a convenient time to do it unless you have some other good reason to work on the CH.

 

[Agile]

One of the problems with boilers is that they only modulate to about 20% to 30% of the maximum.

This will create a greater amount of cycling as your heating is such a low loading.

Most boilers can be set to limit the maximum CH output. Manufacturers dont always encourage installers to set this because they so often mess it up. The energy efficiency regulations do ask for this to be done as it increases efficiency but few ever do it. Many dont even realise its necessary.

Tony

 

[sbrewster2]

Thanks again for all the advice, my plumber was quite impressed when I started mentioning all these things.

I think I'm gonna go for a big combi (WB 40 Cdi) and replace all the rads with doubles (with TRVs).

Hopefully it'll be really good showers and a nice warm flat for me from now on!!

Simon

 

[Monsoon]

Providing you get the flow rate from the mains then its got to be the way to go.

Ive purchased a reasonably spec'ed Vaiiant (yet to be fitted). It was a few hundred pounds more than the cheapies but given the fact that it will cost the same amount to have fitted plus as you say much better shower/bath filling performance plus the reported improved reliability plus 2 years warranty as opposed to 1 year on the cheapies etc etc ... then I think it's a pretty safe bet.

Additionally, a decent amount of power on a shower is certainly on the 'wish/want' lists of a lot of property buyers, so may give you an edge when you sell.

Good luck

 

[Agile]

""" I think I'm gonna go for a big combi (WB 40 Cdi) and replace all the rads with doubles (with TRVs). """

There is no point in replacing the rads. The heat loss is determined by the premises ( unless you open the windows. )

TRvs, whilst necessary only make it worse!

Tony

 

[JohnD]

? But if you have big rads, with a big water content, doesn't that mean the boiler has to blast for longer to get them all hot, then sit and have a rest while they cool down, thus reducing short cycling? I thought oversized rads were A Good Thing?