Max gas load for U6 gas meter.

[frustrateduser]

In short, can anyone tell me what max load of a U6 meter is, is it 65KW or 6m3/hr.
I am looking at two boilers at 30kw and 24kw, plus one gas cook at 9kw, total usage is 63KW/hr which is within the 65KW.
However, if I look at the gas flow rate, 30kw boiler at 3.4m3/hr and 24 KW at 2.59m3/hr. Just two boilers already reach 6m3/hr. Does that mean I need to have a U16 meter in order to have a gas cook.
Many thanks,

 

[BLOD]

U6 has a maximum throughput of 6m3/hr

 

[frustrateduser]

U6 has a maximum throughput of 6m3/hr

Many thanks, BLOD.
However, I understand that the way to convert KW to hours gas rate is to multiply 0.094. So for 6m3/hr equivlant to 64KW. If I didn't ring up the boiler manufacturer to ask for their gas hourly flow rate, I could just calculate two boiler 30kw+24Kw=54KW x 0.094=5 m3/hr plus 9Kw cookx 0.094=0.84m3/hr. The total would be within 6m3/hr.

If you are to issue a Gas Safe Certificate for a landlord, what would you do, do you just calculate the load or check the individual boiler manual?

 

[kirkgas]

you need to take diversity of use into account as well, below is an extract form BS 6400-1 which 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/m
3 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

so using your figures and this table you have 30 + (24 x 0.8) + (9 x 0.6)
30 + 19.2 + 5.4 = 54.6 x 0.094 = 5.13m3/hr

 

[frustrateduser]

Hi, Kirkgas, many thanks for replying. To be honest, I am lost here. Can you give me an example.
I have been liaising with our gas supplier as well as the southern gas network regarding the upgrade. The hoops you have to jump through to get meter changed is unbelievable. No wonder all the new build are no longer using gas.

 

[Orry Clayton]

Kirkgas given you the answer here;

so using your figures and this table you have 30 + (24 x 0.8) + (9 x 0.6)
30 + 19.2 + 5.4 = 54.6 x 0.094 = 5.13m3/hr

Kirk, what is the reason the first boiler (30kw) isn't multiplied by 0.8 also? As I'm still training and jobs are usually on small domestic, so would be nice to know.

 

[diamondgas]

In short, can anyone tell me what max load of a U6 meter is, is it 65KW or 6m3/hr.
I am looking at two boilers at 30kw and 24kw, plus one gas cook at 9kw, total usage is 63KW/hr which is within the 65KW.
However, if I look at the gas flow rate, 30kw boiler at 3.4m3/hr and 24 KW at 2.59m3/hr. Just two boilers already reach 6m3/hr. Does that mean I need to have a U16 meter in order to have a gas cook.
Many thanks,

It's got something to do with net and gross frustrateduser regards the values ... The boiler rating is net but gas consumption is gross ...!

Gas consumption is calculated using a calorific value of
38.7 MJ/m3 (1038 Btu/ft3) gross, or 34.9 MJ/m3 (935 Btu/ft3) nett

I think that's how it works I'd get the supplier to put a U16 meter in

 

[Nostrum]

I'm sure i've heard the meters are capable of pushing through nearer 7m3 even though they are badged for 6?


I'd try it on the U6 first, as i'm sure there will be a charge for a U16 upgrade.

 

[topdog]

To determine the size of the gas meter we require to know the maximum gas flow rate of the Installation.
This can be calculated by using the Manufacturers stated GROSS heat input,
therefore where the manufacturer states a NET figure we require to multiply this by 1.11 (Natural Gas)

Since it is unlikely that all appliances will be on 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.
e.g
1st Combi Boiler 30kw gross x 0.8 = 24.
2nd Combi Boiler 24kw gross x 0.8 = 24.
cooker 9kw gross x 0.6 = 5.4
Total = 53.4 kw

53.4 x 3.6=192.24 Divided by CV of 38.76 MJ/m3 =4.960 m3/hr. If your figures Above are GROSS.

If your figures above are NET: then multiply by 1.11 = 4.960 x 1.11=5.51 m3/hr but still you are within 6 m3/hr of U6 meter but have no room for any expansion.

As I'am a Trainee, Could the experience Gas Engineers tell me if this is correct as I would like to Know if we have been told correct.
as I will be sitting my ACS soon or is there another easier way to do it.
Many Thanks for any suggestions, I would appreciate this.
Paul Wolfe
(topdog)

 

[villa_tom]

you need to take diversity of use into account as well, below is an extract form BS 6400-1 which 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/m
3 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

so using your figures and this table you have 30 + (24 x 0.8) + (9 x 0.6)
30 + 19.2 + 5.4 = 54.6 x 0.094 = 5.13m3/hr

Reading this just made a tiny part of my brain explode :-(

 

[kirkgas]

Kirkgas given you the answer here;



Kirk, what is the reason the first boiler (30kw) isn't multiplied by 0.8 also? As I'm still training and jobs are usually on small domestic, so would be nice to know.

the table gives the first boiler (not a combi as a diversity of 1) must be due to the hot water being heated, but TBH the OP hasnt told us whether the 30kw is a combi or not

 

[kirkgas]

To determine the size of the gas meter we require to know the maximum gas flow rate of the Installation.
This can be calculated by using the Manufacturers stated GROSS heat input,
therefore where the manufacturer states a NET figure we require to multiply this by 1.11 (Natural Gas)

Since it is unlikely that all appliances will be on 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.
e.g
1st Combi Boiler 30kw gross x 0.8 = 24.
2nd Combi Boiler 24kw gross x 0.8 = 24.
cooker 9kw gross x 0.6 = 5.4
Total = 53.4 kw

53.4 x 3.6=192.24 Divided by CV of 38.76 MJ/m3 =4.960 m3/hr. If your figures Above are GROSS.

If your figures above are NET: then multiply by 1.11 = 4.960 x 1.11=5.51 m3/hr but still you are within 6 m3/hr of U6 meter but have no room for any expansion.

As I'am a Trainee, Could the experience Gas Engineers tell me if this is correct as I would like to Know if we have been told correct.
as I will be sitting my ACS soon or is there another easier way to do it.
Many Thanks for any suggestions, I would appreciate this.
Paul Wolfe
(topdog)

topdog this looks ok apart from your calculation for 24kw boiler, you have listed "x 0.8" which is correct but you haven't done the calc and lsited the answer as 24kw

 

[kirkgas]

To determine the size of the gas meter we require to know the maximum gas flow rate of the Installation.
This can be calculated by using the Manufacturers stated GROSS heat input,
therefore where the manufacturer states a NET figure we require to multiply this by 1.11 (Natural Gas)

Since it is unlikely that all appliances will be on 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.
e.g
1st Combi Boiler 30kw gross x 0.8 = 24.
2nd Combi Boiler 24kw gross x 0.8 = 24.
cooker 9kw gross x 0.6 = 5.4
Total = 53.4 kw

53.4 x 3.6=192.24 Divided by CV of 38.76 MJ/m3 =4.960 m3/hr. If your figures Above are GROSS.

If your figures above are NET: then multiply by 1.11 = 4.960 x 1.11=5.51 m3/hr but still you are within 6 m3/hr of U6 meter but have no room for any expansion.

As I'am a Trainee, Could the experience Gas Engineers tell me if this is correct as I would like to Know if we have been told correct.
as I will be sitting my ACS soon or is there another easier way to do it.
Many Thanks for any suggestions, I would appreciate this.
Paul Wolfe
(topdog)

re an easier way, i multiply the max HI by 0.094 to give me the gas rate required, you still need to do the diversity calc (see my earlier post on this, ive given an example at the bottom using the OP's appliances

 

[frustrateduser]

Many thanks for all your reply.
Apparently the meter can push through more than 6m3/hr, but I am told that new boilers are very sensitive unlike old ones, if the pressure drops to certain level, they will automatically shut down. So during peak hours or extremely cold weather, the boilers might not function properlyy. Also I am told that I will fail the Gas Safe Certificate check. But then again British Gas engineer said the max they would allow is 6.3m3/hr. Very confusing!

We are looking at two system boilers with an unvented cylinder not combi boilers, I don't know whether this makes any difference. The house currently has two vented boilers 18years old at 30kw and 24kw, a gas cook and a gas fire. Originally we were looking at them being replaced by two 30kw but concerned about the load.

 

[frustrateduser]

hi, Kirkgas, actually my question is related to your calcuation. You calculate the gas load by using the total KW x 0.094 with diversity factor. But if you use manufacturer's gas flow rate, they are higher than the caluation. Worcester told me the gas flow rate for 30kw system boiler is 3.4 m3/hr, but if you calculate by 30Kw x 0.094 = 2.82 m3/hr which is lower. Which one should I use to work out the max load?

 

[tamz]

It depends on the calorific value of the gas in your area. The amount of gas required to give 30kw of energy varies (quite a bit) throughout the uk. You can usually find what yours is on your gas bill.

 

[John_]

Interesting thread!!

 

[Orry Clayton]

It depends on the calorific value of the gas in your area. The amount of gas required to give 30kw of energy varies (quite a bit) throughout the uk. You can usually find what yours is on your gas bill.

Be nice if there was a website, where you could type in your postcode and it tell you your CV.

 

[tamz]

Unfortunately it is quite hard to find out what the cv is in different parts of the country.
This page gives you an idea up to 2010 (you can change the dates)

Compare Gas and Electricity prices and save up to £200 on your home energy bills

 

[diamondgas]

You'll not get it wrong by putting a U16 in but may by leaving a U6 ... I thing I'd be asking the suppliers to put a larger meter in Justified by your calculations being borderline for a U6 should you be asked ..... IMHO

 

[Bernie2]

It may be of interest. But prior to about 1970 we used Town Gas in the UK. It was manufactured usually from coal or oil. The amount of heat each cubic foot of gas contained could be altered either up or down, so long as it never fell below a government set minimum level. They watered it down using steam if it was too rich. Usually coal or oil had a higher CV than that sent out. And coal or oil was expensive to use, so bulking it out to reduce the CV was money saving. Its why on old systems you have water drain off pockets.

The Natural Gas we have now can vary as Tamz says and that shows once again that using set formulas without checking are only a guide, the CV can change depending what is in the gas.

 

[GrahamM]

Your two boilers, fire and cooker will almost certainly be over the output of a 6 m³/h meter after calculating diversity.
Exact make/model of all your appliances or exact kw figures and wither gross or net will facilitate a more precise calculation.
But, I believe you will almost certainly require a bigger meter.

 

[midge]

As a U16/U25 installer I get this all the time. Just make sure the installation is suitable first. If its in a meter box, semi-concealed or medium pressure its not going to be straight forward (or cheap).

I turned up at a place recently that was being converted into a cafe and was due to open that afternoon. It has a built in meter box. (They didn't open that afternoon).

 

[frustrateduser]

Your two boilers, fire and cooker will almost certainly be over the output of a 6 m³/h meter after calculating diversity.
Exact make/model of all your appliances or exact kw figures and wither gross or net will facilitate a more precise calculation.
But, I believe you will almost certainly require a bigger meter.

Graham M. many thanks for your reply.
We intend to use two Worcester boilers one Greenstar 30CDI (30KW) the other Greenstar 24i system (24kw). Worcester told me the gas flow rates for both are 3.4m3/hr and 2.59m3/hr. I don't know whether they are gross or net. I can ask again. The gas cook is 9KW. don't know the flow rate. The boilers are not connected, they serve different zone, i.e one serve Ground floor and second floor, the other serve first floor and hot water. I don't know whether diversity can still apply in this circumstance.

Will the above information sufficient to do the precise calculation.

 

[frustrateduser]

As a U16/U25 installer I get this all the time. Just make sure the installation is suitable first. If its in a meter box, semi-concealed or medium pressure its not going to be straight forward (or cheap).

I turned up at a place recently that was being converted into a cafe and was due to open that afternoon. It has a built in meter box. (They didn't open that afternoon).

Midge, you are absolutely right. Change to U16 is neither straightforward nor cheap, we are low pressure, but have a built in U6 which is recessed into the wall whilst U16 can only be installed flush with the wall. So the gas supplier can't just change the meter, We have to have the southern gas network to change the meter position before the gas supplier can change the meter. The network has tested the capacity and told us that the max load is 77kw. but as nowdays U16 tend to have a 2inch plastic pipe, they want to upgrade the pipework, which means that they will dig up the road to relay the pipe to connect to the main. Further complication, their drawings don't show where the main is. I will get the quotation from gas network next week. I imagine it will be anything between 5-10k. Gas supplier has already quoted £900 just for chaning the meter.

 

[GrahamM]

Many thanks for all your reply.
Apparently the meter can push through more than 6m3/hr, but I am told that new boilers are very sensitive unlike old ones, if the pressure drops to certain level, they will automatically shut down. So during peak hours or extremely cold weather, the boilers might not function properlyy. Also I am told that I will fail the Gas Safe Certificate check. But then again British Gas engineer said the max they would allow is 6.3m3/hr. Very confusing!

We are looking at two system boilers with an unvented cylinder not combi boilers, I don't know whether this makes any difference. The house currently has two vented boilers 18years old at 30kw and 24kw, a gas cook and a gas fire. Originally we were looking at them being replaced by two 30kw but concerned about the load.

Graham M. many thanks for your reply.
We intend to use two Worcester boilers one Greenstar 30CDI (30KW) the other Greenstar 24i system (24kw). Worcester told me the gas flow rates for both are 3.4m3/hr and 2.59m3/hr. I don't know whether they are gross or net. I can ask again. The gas cook is 9KW. don't know the flow rate. The boilers are not connected, they serve different zone, i.e one serve Ground floor and second floor, the other serve first floor and hot water. I don't know whether diversity can still apply in this circumstance.

Will the above information sufficient to do the precise calculation.

You mention gas fire in previous post. Is this to be taken into account?

With your 2 boilers and cooker it looks like you will have a total flow rate in region of 6.3 m³/h.
Unfortunately it is just over the 6 m³/h capacity for your standard meter, although by very little.

 

[frustrateduser]

You mention gas fire in previous post. Is this to be taken into account?

With your 2 boilers and cooker it looks like you will have a total flow rate in region of 6.3 m³/h.
Unfortunately it is just over the 6 m³/h capacity for your standard meter, although by very little.

Yes the house has a gas fire at the moment. We bought the house 2 months ago and didn't realize the problem. The reason I am looking so closely on the max load is to avoid changing the meter given how difficult it is. We are going to change the gas fire to electric one to save the capacity foe others. I am even looking at heat & loss calculation to see whether 2 new 24kw boilers can replace the old 30kw and 24kw as the new ones has 90% efficiency whilst old one only has 75%. maybe the money saved dor changing meter can be used to insulate the property better.

Graham when you say our load is in the region of 6.3m3/hr did you use the manufacturer gas flow rate or use the 0.094 conversion rate?

 

[Orry Clayton]

We are looking at two system boilers with an unvented cylinder not combi boilers, I don't know whether this makes any difference. The house currently has two vented boilers 18years old at 30kw and 24kw, a gas cook and a gas fire. Originally we were looking at them being replaced by two 30kw but concerned about the load.

If you are changing from vented to unvented, would a single 40kw work just as well?

 

[kirkgas]

The manufacturer will quote you has flow assuming diversity of 1. As that will draw more gas, using diversity calcs looked ok for U6

 

[frustrateduser]

The manufacturer will quote you has flow assuming diversity of 1. As that will draw more gas, using diversity calcs looked ok for U6

Thanks Kirkgas. But when I looked at your diversity table, diveristy factor is 1 if it is central heating appliance. The two boilers are system boilers and zone to serve different area. One for ground, second floor heating. The other for first floor and hot water. Can I still use 0.8 factor for the second boiler?

 

[GrahamM]

No. Can only use 0.8 factor for combi.

 

[phpaul]

the gas transporters work with a 65kw rule of thumb . with only being a little over why not down size one boiler a little . what method did u use to workout the power u need whole house or room by room?
just as a wee story had a massive house with 22 rads and 3 floors =3x heating zones and a solar cylinder (sans solar).
i sized the house with the whole house method and worked out i needed 2 boilers 45kw ish i think. the customer said no cuz his last place had a 35kw and 35 was what he wanted 2years and some bad winters later his house it fine throu the awful weather we have had.

 

[DaveTidy]

The local CV of your gas is generally on the household gas bill, normally under the 'Ccalculating the cost of the gas used' bit. It is still there as i've just checked one just in case you need it in the future.

 

[R1CKY]

Thought I'd drag up an old topic instead of a new one. Just read about the diversity factor above, am I right in saying that if there are only two appliances, the diversity factor is 1 for both appliances?

I'm pricing a job in which a customer wants an additional combi boiler fitted to the extension (don't ask!) The existing boiler has a gross heat input of 31.5Kw and the new one for the extension has a gross heat input of 37.7Kw. Obviously if the diversity factor is 1 for two appliances, it'll have a requirement of 69.2Kw, which is too high. The guy at Gas Safe Technical told me the max is 63Kw for a U6.

 

[lame plumber]

just had a quick look and surely the most important thing to do would be as mentioned a proper analysis of heat loss calcs for the property to acertain the exact heating reqirements. Its then possible to probably reduce the boiler output needed, especially if additional insulation etc is being installed. Running one properly zoned boiler has got to be better than two, and cheaper in gas costs in the long term.