Which boiler?

[alisyed1]

Hi there,

First post. I am currently in the process of deciding which boiler to have installed in my flat ( 4 bedrooms, 1 bathroom and 1 en-suite). The main bathroom has a bath and a thermostatic mixer bar. I haven't decided whether to install a thermostatic mixer or an electric shower in the en-suite yet. There are 9 radiators in the property with two of them being monstrous 2 metre long by 600 high double convectors.

The supply gas pipe from the meter to the current boiler is in 22mm pipe, the length of run is approximately 24 metres.

The cold water main is old copper pipe sizing of 21mm. Pressure was measured at just under 4 Bar with a flow rate just over 21 litres per minute. This was measured at the kitchen sink mixer tap.

The run from the boiler to the bathroom is also approximately 25 metres.

I don't have the space for an indirect un-vented cylinder or the mains flow rate required for it as suggested on this forum. So I am limited to large combi's.

My first two options were the Worcester Bosch 42cdi and the Vaillant ecoTEC plus 937. After spending some time reading through the forum, would the Veissman Vitodens 222-F be suitable for my installation.

I am trying to get the most efficient system I can get that can adequately supply the hot water requirements for four adults and two young boys.

Thanks.

 

[gassafe]

4 bar pressure with 21 litres per minute sounds okay for un-vented cylinder to me, it would probarly be my recommendation if there are 4 adults and 2 kids in the house also.
Although if your set on a combi then a Worcester Bosch all the way =]

 

[adrian816]

When I phoned different companies for advice before having a new central heating system installed one person told me " get a boiler with a stainless steel heat exchanger, they last longer ". I've got a Vaillant ecoTec combi and I'm very happy with it.

 

[REDSAW]

welcome to the forum

 

[Blackcatgas]

If youve got the space the 222f will be more than adequate for your needs,Ive fitted/look after 3 of them and there will be one being installed in BlackCatGas towers after xmas as iam really impressed with them.
It includes a 200 series combi boiler which is a peach of a boiler , it will make full use of your 20ltrs a minute flow rate, get the weather compensation control kit for extra savings, the new control unit is like an Ipod and very easy to use.
The boiler is quite expensive (but good value for the money when you consider what you are getting for your money).
It is very heavy (100kg) so make sure youve got some strong mates to get it up the stairs.
Iam a Viessmann aproved installer and I can go on a bit too much about thier products but the 222f really is an excellent piece of kit.

 

[Yorkshire Jim]

You may need to check your gas pipe between the meter and the appliance, as it may need an upgrade.

A Worcester Bosch 42CDi requires 4.4 cubic metres of gas per hour. You have mentioned that the length of your gas pipe is 24m of 22mm copper. If this is the linear length, I am going to use that as the actual pipe length and add on only 2x elbows for this exercise. This would take the equivalent length to 25m (2x elbows at 0.5m each).

Now to the proper number crunching:
An equivalent pipe length of 25m of 22mm copper tube (BS1057) will only deliver around 2.6 cubic metres per hour of gas with a 1mbar drop from end to end.

Bear with me:
This would mean that in theory, a 22mm copper pipe with an equivalent length of 25m would have a pressure drop of 2.5mbar.

So what does this mean? The boiler would probably appear to be running ok. The maximum heat output would be compromised. This would be more noticed in DHW mode when the boiler would be in full flame. As the boiler would not be reaching it's full output, the amount of hot produced would be lower than specified in the manual.

An unvented hot water cylinder would be a wiser option, as less energy is required to maintain the temperature of a large mass of water, than it is to heat up 18 litres per minute or so of water by 30°C coming in at 10 - 15°C.

Hope that helps.

 

[Yorkshire Jim]

You may need to check your gas pipe between the meter and the appliance, as it may need an upgrade.

A Worcester Bosch 42CDi requires 4.4 cubic metres of gas per hour. You have mentioned that the length of your gas pipe is 24m of 22mm copper. If this is the linear length, I am going to use that as the actual pipe length and add on only 2x elbows for this exercise. This would take the equivalent length to 25m (2x elbows at 0.5m each).

Now to the proper number crunching:
An equivalent pipe length of 25m of 22mm copper tube (BS1057) will only deliver around 2.6 cubic metres per hour of gas with a 1mbar drop from end to end.

Bear with me:
This would mean that in theory, a 22mm copper pipe with an equivalent length of 25m would have a pressure drop of 2.5mbar.

So what does this mean? The boiler would probably appear to be running ok. The maximum heat output would be compromised. This would be more noticed in DHW mode when the boiler would be in full flame. As the boiler would not be reaching it's full output, the amount of hot produced would be lower than specified in the manual.

An unvented hot water cylinder would be a wiser option, as less energy is required to maintain the temperature of a large mass of water, than it is to heat up 18 litres per minute or so of water by 30°C coming in at 10 - 15°C.

Hope that helps.