TOSS UP FOR WHAT BOILER FOR THIS FLOW RATE?

[zappastix]

Hi

Last week "dean7445" explained to me about how to work out what new boiler is best for the "flow rate".

I have added up all the current radiators, including additional radiators as there might be a change of
property layout upstairs.

That is I've added all BTU's and kW's

The reason for this post is to ask what boiler should I go for BECAUSE they are both close to the wire
regarding the flow rate - but one boiler output might struggle and the other fits comfortably.

So my flow rate is 12 litres per minute.

Total KW for all radiators = 36,044kW
Total BTU for all radiators = 123,062 BTU

Both of the following boilers are the same for Central heating output: 30kW

So I'll reduce the amount of radiators or BTU to go no higher than 30kW
(i.e. knock off over 600kW across the rads (down from 36,044kW) )


Here are the two boilers - which one would you go for.

I'd prefer to throw a small amount of money down the drain ever time its working,
if it means the boiler will not struggle OR be right on its limits every time is fires up.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Greenstar 29CDi Classic

Central heating output: 30kW
Domestic hot water flow rate: 12.3 litres per minute at 35 degree temperature rise
(provided adequate mains pressure is available)

Designed operational flow rate 11 litres per minutes at 40 degree temperature rise.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Greenstar 34CDi Classic

Central heating output: 30kW
Domestic hot water flow rate: 14.3 litres per minute at 35 degree temperature rise
(provided adequate mains pressure is available)

Designed operational flow rate 12 litres per minutes at 40 degree temperature rise.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


So I'm confused about;

Domestic hot water flow rate -VS- temperature rise -VS- designed operational flow rate


Many thanks in advance.

Stephen

 

[Dan Robinson]

I trust the crap they publish anyway.

Boilers are crap.

Their literature is even worse.

Had to service a Highflow this morning and the errors and omissions in the book was shocking.

. Installers Choice my arris..

 

[JohnD]

calculate the heat loss for the house.

For all we know, the radiators might be too big or too small (too small is worse).

There are numerous calculators. Try this one http://calculators.baxiknowhow.co.uk/boiler-sizing/

If the house has had improved insulation since it was built, heat loss will have reduced.

A house that needs 30kW of heat is very big and/or very old

If you have TRVs and do not live in a greenhouse it will be very rare for all your radiators to be full on at the same time anyway. Perhaps if you have been on holiday in winter and have just come home to a freezing house because you do not have a programmable stat.

Presumably the house only has one bath or shower.

 

[bolshy]

Oversize your radiators a bit, get a BAXI registered installer to put in a Duotec HE A 40kw combi in. You'll get a 7 year warranty, tried and tested technology. I've installed loads and never had a single problem with them. Don't get the Gas Adaptive model, make sure it's the HE A version.
Most hot water flow rates are quoted to raise incoming mains temp by 35 ° C.
In a large property, separate time and temperature controlled heating zones should be installed to save lots of money on heating bills.

 

[bolshy]

By the way, the Duotec 40 kW gives 16 l/pm at 35 ° C rise and 34 kW net input (condensing) into heating (36 kW gross).

 

[St0rmer66]

bolshy, only the 28kw version is available in LPG.

Always oversize for hot water, 35 degree rise is awful when the incoming main is at 5 degrees or less! 40 degree is better figure to use but usually hidden away in the instructions or completely omitted .

That said, is your water so terrible on the current 28kw Alpha? If so, as I mentioned in the other thread, a new boiler will give a better output despite also "only" being the same rating (less power loss from inefficiency).

 

[bolshy]

I must have missed where the OP wrote LPG :/

 

[bolshy]

I think you'll find standard Duotec combi for LPG goes up to 33 kW. The GA version has a 40kW model.

 

[St0rmer66]

I must have missed where the OP wrote LPG :/

It was in the last thread, so I think you're forgiven there .

I think you'll find standard Duotec combi for LPG goes up to 33 kW. The GA version has a 40kW model.

Not that I can find. Maybe since it became the "HE A" as opposed to "HE" they dropped it. Don't get me wrong, I like them... got a 40 HE A in my own house. But if he wants 30kW+ he might have to look elsewhere.

 

[holty]

Rinnai water heater tied in with a good heat only boiler with system kit or system boiler. Might be out of scope for some people, but will get a good water flow rate from the water heater without affecting ch. The rinnai twinflow was a great option but no longer available. Word is rinnai are field testing there own ch boiler with water heater. All this is obviously due to how much you want to spend. Viessmann 111 is not bad but bloody massive on the wall.

 

[dreadnoughtheating]

Two Heatline Capriz's.
one each for upstairs and downstairs, then when one packs up (applicable to any combi....), you've still got half the house heated and hot-water.

Never done it myself you understand, waiting for the other's to shoot this one down.

DH

 

[zappastix]

Hi

First chance to get back and wrap this post up.

Just thought I'd add what the final outcome is going to be for those
that have followed other posts connected to this one - purely to help
anyone else who might find themselves in a similar situation.

I have included this post to the others posts connected.

I looked in to other boilers that others recommended.

I also checked other web sites with Boiler Installers recommendations
who on balance rated Worcester Bosch Greenstar **CDi Classic
as the boiler to go with.

Briefly a while back I did a flow rate test - 10 seconds gave me two litres.

So this equated to 12 litres per minute.

The boiler to be replaced was an Alpha 28CB.
The 12 litres per minute would have matched the Alpha.

I nearly went for Greenstar 29CDi Classic LPG - because that was the nearest
to the Alpha . . . . BUT I thought I best double check flow rate again.

This time I did a FULL 60 SECONDS and this resulted in exactly 14 litres per minute.

I really don't understand this discrepancy, (12 vs 14) but this is what it came out as.

So I phoned Worcester Bosch main help line - the woman didn't have a clue what I was asking
about and put me through to Technical dept.

The guy said the two boilers that I thought would be okay the
Greenstar 34CDi Classic OR Greenstar 38CDi Classic were both okay with 14/lpm

He said he'd go for the "38CDi" because it delivers 14 litres per minutes at 40 degrees.

And because it's not more than around £150 I'm going to go for the Greenstar 38CDi Classic LPG

I asked about an installer, he said if you use a local Gas Safe guy I wouldn't receive 7 years
(8 with fitted filter) parts & labour guarantee BUT I would get 5 years parts & labour guarantee.


For those interested Greenstar info;

Greenstar 34CDi Classic

Central heating output: 30kW
Domestic hot water flow rate: 14.3 litres per minute at 35 degree temperature rise
(provided adequate mains pressure is available)
Designed operational flow rate 12 litres per minutes at 40 degree temperature rise.


Greenstar 38CDi Classic

Central heating output: 30kW
Domestic hot water flow rate: 16.4 litres per minute at 35 degree temperature rise
(provided adequate mains pressure is available)
Designed operational flow rate 14 litres per minutes at 40 degree temperature rise.

Many thanks again - I couldn't have got here eventually without helpful snippets here and there.

Stephen

 

[Agile]

Briefly a while back I did a flow rate test - 10 seconds gave me two litres.

So this equated to 12 litres per minute.

The boiler to be replaced was an Alpha 28CB.
The 12 litres per minute would have matched the Alpha.

This time I did a FULL 60 SECONDS and this resulted in exactly 14 litres per minute.

Stephen

Oh dear!

You don't seem to realise that to properly check the flow rate before fitting a combi you must find the dynamic flow rate. In litres per minute at a chosen pressure, usually 1.0 bar. See the FAQ for an explanation.

In a house with 36 kW of rads ( and you should NOT reduce the size of rads! ) I am surprised that you want to fit a combi boiler. They only supply one hot outlet at a time.

So it seems you have a large house and must heat every one of the perhaps 15 rooms but only want to take one bath/shower at a time.

If there is only two people living there then you can turn off the heating in unoccupied rooms.

Worcester are not the only boiler manufacturer!

Many would recommend other makes!

Tony

 

[JohnD]

We still don't know if 30kW has been calculated as heat loss of the house. The radiator sizes may be incorrect.