COMBI OUTPUT QUESTION

[pasty-man]

Can someone advise me on this please!
Im looking at purchasing a combi boiler for a 2 bedroom house. Im particularly looking for a good DHW flow rate for a thermostatic mixer shower.
Having looked around at boilers available I feel drawn towards a Vaillant turbomax plus 828 maybe even the 837 but the question is.....

My central heating requirements are only about 28,000 btu's/hour (8.2kw)
but the boilers im looking at have a spec of CH output range of 35,500 - 95,500 btu's.
Will this be a problem??
Will I require any TRV's (or would this be to 'restricting' for the heating system. If this is the case is a roomstat in the living room the option.

Would it be pointless looking at a condensing combi in this scenario?
Im sure ive read that for true efficiency your requirements should be round about the max output!?

 

[IanDB]

Im sure ive read that for true efficiency your requirements should be round about the max output!?

You're right on that point. The boiler won't work efficiently if it's trying to pump too much energy into a small system, I believe it will keep starting up and shutting down. This is then compounded once the TRVs kick in as they will reduce the flow even further.

All new systems are fitted with TRVs. They allow you to control the temperature of each radiator (i.e. not either boiling hot or stone cold)- particularly useful in bedrooms. You can get away without them if you balance your system properly but they serve a purpose.

Sorry, but I can't be much help on boiler selection, Vaillant appear to be farirly reliable though.

 

[pasty-man]

Sounds about right but can anyone explain this to me...
I consider the house to be a particularly average 2 bedroom with average heating requirements. Is it that out of the ordinary to want a higher hot water flow rate but not as great heating output??
The only option I can see is to go for a little model of some description, but this is only going to give a just acceptable hot water flow rate?
I really want the best flow rate I can achieve, can anyone comment if/how I can use a high output combi to achieve?

 

[DP]

I would fit a bogstandard combi and an UV cylinder. No combi will touch this setup. AND you have facility to heat water when the boiler chucks it (and it will- on a Friday). Fill a bath in arounf two minutes and shower that will drown you. Combi could supply water to kitchen.

 

[pasty-man]

Great!! getting somewhere.
Could you suggest a Vaillant model in this scenario?

 

[DP]

Does not have to be a Vaillant. Vaillants are not what they use to be. Some swear by Vaillants, Worcesters or their favourites. Have fitted these (by the book) and had trouble with them as well. Mostly repair boilers so can suggest Vokera as a make that is reasonable for spares when the boilers does break down.

Look at 80,000 BTU boiler. Flame will downsize to load. Vokera Linea range fires at 75% rate for first 15 minutes. If heat load not satisfied (unlikely to be a problem for you), it will go to full rate.

If you are going the uncondensing route, do hurry as these boilers are be 'sold off' in anticipation of condensing only sales.

If going the condensing route, I would only look at stainless steel heat exchanger boilers.

 

[pasty-man]

Thanks very much for your advice so far!!
Thats me almost 'advised'....
Last thing though, the thermostatic mixer I beleive requires relatively equal pressures from hot and cold so would I be ok do you think with something like a vantage unvented cylinder which delivers 15 l/m @ 60 degrees and my mains flow coming at approx (jug measured) 20 l/m?

 

[pasty-man]

ps
why not a vented system?

 

[DP]

Vantage is dedicated to Vaillant.

UV systems will give you balanced feed.

Above can only be fitted by those who hold the UV ticket. Very dangerous in hands of untrained.

Vented? I give up

 

[pasty-man]

Im done.
Its late.
I see the light.
Thanks DP for your wisdom.
Now I go source.

Hey thanks again, consider that your good deed of the day helping fellow man and all........