Max gas load for U6 gas 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.

 

[R1CKY]

Oh believe me, if I was designing it, there wouldn't be another boiler, but the customer has a spare Baxi Duotec 33HE lying around that he wants to fit in his extension which has a bathroom and 3 rads!! Looks like he can't have the boiler in there anyway, which suits me as the gas run would be a nightmare!!

 

[lame plumber]

run away............

 

[tamz]

Diversity can be a strange one.
One or 2 appliances you shouldn't apply diversity so your 2 boilers at 69.2kw would need approx 6.39m3/hr

However add a 7kw hob and you would have (assuming they are both combis) 69.2 x 0.8 = 55.36kw, 7kw hob x 0.6 = 4.2kw total 59.56kw = 5.5m3/hr so they are fine!

The wierd and wonderful rules of gas :lol:

 

[R1CKY]

That is exactly the situation I'm in! If I fit a hob, I could run all three appliances and be within the regs!