Gas boiler KW question

[steved101]

Just a quickie - when a boiler says it has a heat input (or output) of say 18-21 KW ... what does this mean... is it the amount of gas it uses ????

 

[D_Hailsham]

Just a quickie - when a boiler says it has a heat input (or output) of say 18-21 KW ... what does this mean... is it the amount of gas it uses ????

There will be two figures given: heat input; heat output.

The input is what the boiler actually consumes, as measured by your gas meter and charged on your bill.

The output is the amount of heat which is used to heat the water. The difference between the two figures is the heat lost inside the boiler - warming the casing, escaping up the flue etc.

The ratio output/input gives the efficiency of the boiler.

 

[steved101]

Thanks for helping me D_Hailsham, much appreciated.

Is the heat input (gross/net) the amount of gas burned per hour then?

 

[D_Hailsham]

Is the heat input (gross/net) the amount of gas burned per hour then?

No, it's the amount of energy used per second. A watt is a hybrid unit - it is a short hand way of saying one Joule per second. A Joule is a measure of energy.

So a 10kW boiler is using up 10,000 joules of energy every second.

A kilowatt-hour is 3,600,000 joules.

Look at you gas bill and you will see the formula used to convert your consumption (cubic metres or cubic feet) into kilowatt-hours. The gas companies charge by the kilowatt-hour.

 

[Agile]

Thanks for helping me D_Hailsham, much appreciated.

Is the heat input (gross/net) the amount of gas burned per hour then?

Its simpler to answer that the xx kW rating of the boiler is the rate at which power is being used.

In one hour the boiler will then use xx kW/h which is then the energy used in one hour.

Tony

 

[thegasassessor]

Just a quickie - when a boiler says it has a heat input (or output) of say 18-21 KW ... what does this mean... is it the amount of gas it uses ????

Just joined forum so apologies for late response but i don't like incorrect answers.

18-21kw would indicate the appliance is range rated to operate between 18-21kw. This means the engineer would determine what he wanted the appliance to be set at based on how many bathrooms/rads floors and heat losses in the property [Part L building reg's].

When the appliance is set at let's say 18kw the engineer would calculate the ventilation based upon the HIGHEST available setting of the appliance, so 21kw - 7kw x 5cm2 [if open flued].

Now the manufacturers instructions would quote either Gross or Net in the technical section or it would be on the data badge on the appliance. If it's quoted as net and you wish to convert to Gross you would x by 1.1. To do the opposite of converting Gross to Net you would divide by 1.1.
This is written on page 14 of BS5440-2 - 2009 section 6.3.1.

The difference between heat input and heat output is simple, let me try and explain.
The heat input is the Gas coming in from the meter which is calculated after doing the m3hr to kw which could lets say be a Gas fire rated at 6kw [this fire would use 6kw of Gas]. From an engineers perspective he has to design the pipework to supply sufficient Gas to provide 6kw of Gas and check his work afterwards hoping there is no more than 1mb drop from the meter to the appliance [if pipe undersized the kw will not be achieved and should be investigated]
The fire should quote a heat output which is how much 'useful heat' is actually obtained into the room, so lets say the heat output is 3kw and the input is 6kw then it has an efficiency of 50% or for every £1.00 you spend on Gas 50p is going up the chimney wasted!! The appliance manufacturer may bring the efficiency up by testing in a lab and through better heat exchanger design a higher efficiency which is usually reflected in the cost.
Hope this helps other confused people.

Come to me for your ACS.

 

[Agile]

You may end up regretting registering for this forum!

So EXACTLY how would the engineer measure the pressure loss from meter to boiler?

If using a water gauge then how accurately can that be read?

Taking that figure into account, then what is the accuracy of his pressure loss measurement?

You should register for the CC part of this site where the more interesting discussions go on.

Tony

 

[Dan Robinson]

 

[bazdaman]

I look forward to some hearty combustion chamber discussions with you and some of our more forward users!

 

[kidgreen61]

Just a quickie - when a boiler says it has a heat input (or output) of say 18-21 KW ... what does this mean... is it the amount of gas it uses ????

Just joined forum so apologies for late response but i don't like incorrect answers.

18-21kw would indicate the appliance is range rated to operate between 18-21kw. This means the engineer would determine what he wanted the appliance to be set at based on how many bathrooms/rads floors and heat losses in the property [Part L building reg's].

When the appliance is set at let's say 18kw the engineer would calculate the ventilation based upon the HIGHEST available setting of the appliance, so 21kw - 7kw x 5cm2 [if open flued].

Now the manufacturers instructions would quote either Gross or Net in the technical section or it would be on the data badge on the appliance. If it's quoted as net and you wish to convert to Gross you would x by 1.1. To do the opposite of converting Gross to Net you would divide by 1.1.
This is written on page 14 of BS5440-2 - 2009 section 6.3.1.

The difference between heat input and heat output is simple, let me try and explain.
The heat input is the Gas coming in from the meter which is calculated after doing the m3hr to kw which could lets say be a Gas fire rated at 6kw [this fire would use 6kw of Gas]. From an engineers perspective he has to design the pipework to supply sufficient Gas to provide 6kw of Gas and check his work afterwards hoping there is no more than 1mb drop from the meter to the appliance [if pipe undersized the kw will not be achieved and should be investigated]
The fire should quote a heat output which is how much 'useful heat' is actually obtained into the room, so lets say the heat output is 3kw and the input is 6kw then it has an efficiency of 50% or for every £1.00 you spend on Gas 50p is going up the chimney wasted!! The appliance manufacturer may bring the efficiency up by testing in a lab and through better heat exchanger design a higher efficiency which is usually reflected in the cost.
Hope this helps other confused people.

Come to me for your ACS.

WTF, I'll resit my ACS elsewhere, thankyou

 

[spudkey]

Proves what a joke the acs system and most assesment centers are

 

[Agile]

I look forward to some hearty combustion chamber discussions with you and some of our more forward users!

I looked over my shoulder when I read that!

 

[misterdubya]

Just a quickie - when a boiler says it has a heat input (or output) of say 18-21 KW ... what does this mean... is it the amount of gas it uses ????

Just joined forum so apologies for late response but i don't like incorrect answers.

18-21kw would indicate the appliance is range rated to operate between 18-21kw. This means the engineer would determine what he wanted the appliance to be set at based on how many bathrooms/rads floors and heat losses in the property [Part L building reg's].

When the appliance is set at let's say 18kw the engineer would calculate the ventilation based upon the HIGHEST available setting of the appliance, so 21kw - 7kw x 5cm2 [if open flued].

Now the manufacturers instructions would quote either Gross or Net in the technical section or it would be on the data badge on the appliance. If it's quoted as net and you wish to convert to Gross you would x by 1.1. To do the opposite of converting Gross to Net you would divide by 1.1.
This is written on page 14 of BS5440-2 - 2009 section 6.3.1.

The difference between heat input and heat output is simple, let me try and explain.
The heat input is the Gas coming in from the meter which is calculated after doing the m3hr to kw which could lets say be a Gas fire rated at 6kw [this fire would use 6kw of Gas]. From an engineers perspective he has to design the pipework to supply sufficient Gas to provide 6kw of Gas and check his work afterwards hoping there is no more than 1mb drop from the meter to the appliance [if pipe undersized the kw will not be achieved and should be investigated]
The fire should quote a heat output which is how much 'useful heat' is actually obtained into the room, so lets say the heat output is 3kw and the input is 6kw then it has an efficiency of 50% or for every £1.00 you spend on Gas 50p is going up the chimney wasted!! The appliance manufacturer may bring the efficiency up by testing in a lab and through better heat exchanger design a higher efficiency which is usually reflected in the cost.
Hope this helps other confused people.

Come to me for your ACS.

Are you related to Joe-90 or Drivel?

 

[ianmcd]

WOW what a great first post good luck on here matey

 

[bazdaman]

I looked over my shoulder when I read that!

Your definatley one of them Tony