If the existing combi boiler is fine, which I assume it is. Just add another combi, then divide and rule. Moving the existing combi is not a big deal. Why spend a fortune on a new system boiler and unvented cylinder when a new combi supplementing the existing can do it.
Advice on combi boiler
- Thread starter low drains drifter
- Start date
Nice one, and the gas meter?
It's a shame that you don't make it clear to the punters that you're not a professional heating engineer as some may be taken in by your advice.
Could you tell us how many combi boilers can be run at once from a standard gas meter? Don't forget to factor any fires, hobs or cookers into your equations.
Nothing has changed since you used to recommend the 54kW ethos boilers has it????
Edit: I see Dan beat me too it
It is prats like Harrison that I suggested some form of demarcation of professional and Googlewomble when the forum had its face-lift 
And that's exactly why it should be made clear to the public that you don't have a clue
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Does diversity factor come in to play JH?
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Really?
Crack on.
Crack on.
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You ask razor if he can add, yet you claim 6m3/hr to be 62kw.
You then don't correctly understand diverisity because Google won't help you?
Diversity is applied with how many appliances?
The factor for a combi boiler is?
Have matron tuck you early, you need your sleep and don't forget to take your medication.
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Maybe JH can tell us diversity factors for the following...
Combi boiler.
System boiler.
Gas cooker/hob.
Gas fire.
I'm all ears and willing to learn , especially so from the cock sure googler JH.
Combi boiler.
System boiler.
Gas cooker/hob.
Gas fire.
I'm all ears and willing to learn , especially so from the cock sure googler JH.
Harrison couldn't give you the diversity of a bag of pick 'n mix let alone a gas installation.
The man is an idiot.
The man is an idiot.
Perhaps you can provide the diversity of a bag of pick and mix, or explain how any form of diversity can be applied to a bag of pick and mix.
Maybe some of Mr Harrison's opinion, advice and comments are wrong in which case you would be more effective in helping ( protecting ) DIYers by explaining the errors Mr Harrison has made rather than making derogatory comments about the person.
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You really have no idea.
Fancy a wager?????
If you can answer these correctly, i'll stick to drains, if you can't how about you stop with the bad advice?
The British standard for domestic low pressure gas meters is?
6m3/hr is how many KW?
Diversity is?
Diverisity is applied with how many appliances connected?
Diversity factor for a Combination boiler when being applied is?
When you know the answer to the above, answer the following..
Can3x24kw combis be ran from 1 6cu meter, if so why/why not?
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An extract form BS 6400-1 which actually tells you how to calculate the actual load
Annex A (normative) Sizing of meters
A.1 Diversity factor
A diversity factor is given to each type of appliance according to the normal degree of intermittence of use. Where there is only one or two appliances (e.g. combination boiler and cooker) the diversity factor shall have a value of one. Where there are more than two appliances the diversity factors listed in Table A.1 shall be used.
A.2 Meter size calculation
To calculate the size of meter required, multiply the maximum heat input of each appliance by its diversity factor, add these figures, convert to megajoules, and divide the total by the calorific value of the gas (typically 39 MJ/m3 for 2nd family gas). The following is an example of such a calculation.
Table A.1
Diversity factors of appliances for meter sizing
Appliance Diversity factor
We need to know the maximum gas flow rate of the installation. This can be calculated by using the makers stated GROSS heat input. Where the makers state a NET figure we have to multiply this by 1.11 (Natural Gas)
As it is unlikely that all appliances will be on full load at any one time, a diversity factor is applied where there is more than two appliances depending on each appliances level of use. Where there is only one or two appliances installed no diversity factor is applied with the gas consumption calculated on the total heat input of the installation. If only two combis are fitted then a diversity factor is not needed to be calculated.
e.g.:
53.4 x 3.6 = 192.24 Divided by CV of 38.76 MJ/m3 = 4.960 cu m/hr. If the appliance figures above are GROSS.
If the appliance figures above are NET then multiply by 1.11 = 4.960 x 1.11 = 5.51 cu m/hr. Well within a U6 meter's capacity with lots to spare. The meter has an overload and can pass more than 6 cu mtrs/hr. The diversity factor allows the stated limit of the meter to be exceeded, but on an intermittent not permanent basis. A U6 meter has an overload of 100%.
Such fun. The OP can cheaply and easily install an additional combi and even have a hob.
Annex A (normative) Sizing of meters
A.1 Diversity factor
A diversity factor is given to each type of appliance according to the normal degree of intermittence of use. Where there is only one or two appliances (e.g. combination boiler and cooker) the diversity factor shall have a value of one. Where there are more than two appliances the diversity factors listed in Table A.1 shall be used.
A.2 Meter size calculation
To calculate the size of meter required, multiply the maximum heat input of each appliance by its diversity factor, add these figures, convert to megajoules, and divide the total by the calorific value of the gas (typically 39 MJ/m3 for 2nd family gas). The following is an example of such a calculation.
Table A.1
Diversity factors of appliances for meter sizing
Appliance Diversity factor
Central heating appliances (other than combination boilers) 1.
Unit heaters 1.
Circulators 1.
Combination boilers 0.8.
Instantaneous water heaters 0.8.
Sink water heaters 0.6.
Room heaters 0.6.
Tumble dryers 0.6.
Hotplates 0.6.
Ovens 0.6.
Cookers 0.4.
Refrigerators 0
---------Unit heaters 1.
Circulators 1.
Combination boilers 0.8.
Instantaneous water heaters 0.8.
Sink water heaters 0.6.
Room heaters 0.6.
Tumble dryers 0.6.
Hotplates 0.6.
Ovens 0.6.
Cookers 0.4.
Refrigerators 0
We need to know the maximum gas flow rate of the installation. This can be calculated by using the makers stated GROSS heat input. Where the makers state a NET figure we have to multiply this by 1.11 (Natural Gas)
As it is unlikely that all appliances will be on full load at any one time, a diversity factor is applied where there is more than two appliances depending on each appliances level of use. Where there is only one or two appliances installed no diversity factor is applied with the gas consumption calculated on the total heat input of the installation. If only two combis are fitted then a diversity factor is not needed to be calculated.
e.g.:
- 1st Combi 30kW gross x 0.8 = 24.
- 2nd Combi 30kW gross x 0.8 = 24.
- hob 9kw gross x 0.6 = 5.4
53.4 x 3.6 = 192.24 Divided by CV of 38.76 MJ/m3 = 4.960 cu m/hr. If the appliance figures above are GROSS.
If the appliance figures above are NET then multiply by 1.11 = 4.960 x 1.11 = 5.51 cu m/hr. Well within a U6 meter's capacity with lots to spare. The meter has an overload and can pass more than 6 cu mtrs/hr. The diversity factor allows the stated limit of the meter to be exceeded, but on an intermittent not permanent basis. A U6 meter has an overload of 100%.
Such fun. The OP can cheaply and easily install an additional combi and even have a hob.
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