How much gas does/can a combi boiler use? (running off tank)

[sidekickdmr]

Simple question, and hopefully a simple answer, if you had an insulated building, say 500-800 SQft, with wet under floor heating, wet towel rads and bathroom and kitchen hot taps being run from a new worcester bosch combi boiler, roughtly how much gas would it use?

Lets assume a couple living there full time, but also have a log burner in the lounge for heat.

I understand this will change vastly summer to winter so can we assume winter, as a worst case senario.

I’m looking to run it off calor tanks, probably 2x 19kg bottles with a auto switchover regulator like this:

https://www.amazon.co.uk/dp/B005C9VVFM/ref=wl_it_d...

I’ve no idea if 19Kg's of gas would last a day or a month.

Thanks

[megaphone]

Modern sited caravans run like this. I know a friend who has one using the bigger 49kg? tanks. He said it eats gas in the winter, a tank lasts 3-4 weeks.

The average natural gas usage for a house is 14,500 KwH. Maybe you can work it out from there.? https://www.londongases.co.uk/blog/how-do-i-know-h...

[V8RX7]

Really depends on the insulation - as you are aware a super insulated house with solar gain needs virtually no heat.

A static caravan with very poor insulation gets through a 47kg bottle within a month in winter.

The gas bottle prices are horrific (per kg of gas) for the smaller bottles.

A 19kg bottle will run my wife's gas hob for almost a year

Edited by V8RX7 on Tuesday 13th December 19:10

[dirkgently]

A 19kg cylinder will have a take off rate of about 1.3kg/h or about 18kW, too little for most combi boilers. You need a 47kg cylinder.

[dsl2]

Ideally you'd want a minimum of a pair of 47Kg bottles to stop them freezing up when under peak gas take off demand, as for usage running our highly insulated temporary accommodation above an oak framed garage of approx 90 sq mtrs with underfloor heating / towel rail / gas hob with Mrs at home all day & running at 23 degrees we've used four 47kgs since April until mid October.

Usage will go up considerably running this internal temps throughout winter no doubt!

[sidekickdmr]

I know 47KGs would be better, but access to the building is bad so it will involve carrying them, any way of making the 19KGs work/flow more? or a smaller boiler with less usage/flow?



Taking this back to the drawing board completely for a min.

I know mains gas is cheaper than mains electric, how would I compare the cost of bottled gas compared to using electric?

I could either install an electric boiler and still use wet UFH etc, or use electric heating and electric water heater for taps.

Is there a simple equation? like one KWH of heating uses X amount of electric or X amount of gas?

[Jambo85]

Someone here seems to have done the hard work for you:

http://www.confusedaboutenergy.co.uk/index.php/dom...

It shows that Propane cylinders of the sizes you are talking about should be about 25% cheaper than electricity. Mains gas or bulk LPG (which I assume means having a substantial permanent tank) is more like 70% cheaper than electricity.

[dsl2]

19kg's will do the same job as 47kg's, just run out quicker!

As long as you use a pigtail to join a couple of bottles together to reduce the gas boil off as mentioned previously it will work just as well, no reason why if you have the space not to pig tail 4 together & use an OPSO auto change over unit to switch automatically between the pairings when one runs out.

All these parts available from your local main gas agent

[V8RX7]

I just googled as I have carried 47kg bottles and remember they were heavy... 97kg !

I would add that I found it impossible to buy LPG fittings etc locally and I can highly recommend BES with next day delivery

https://www.bes.co.uk/index.asp

[abzmike]

We moved into our house a couple of years ago, built in 2011 in Aberdeenshire. Four beds and seemingly pretty well insulated. No mains gas, and the chap who built the place seemed to cut a few corners so we have a combi, for central heating and hot water, no underfloor heating, just normal radiators, running off 47kg bottles. We do have a pretty chunky log burner that heats the lounge great once it gets going.

Bottles are currently £60 each delivered - I have a trolley to move them from the end of the drive where they get dropped by the Calor guy, but they are a bit of a grapple to move around and change.. This time of year we last 2 weeks if we are very careful, in the really cold weather a good bit less. In summer we hardly used the heating, so a bottle lasts 6 weeks or more. Getting a bulk tank installed is a possibility, the challenge is finding an accessible spot far enough from the house.

I think our boiler is pretty feeble, but to be fair could probably use a service. I'll mention it to the plumber who is coming any day to fix the pressure tank atop our mains water pump that burst one very cold night last week - but that's another story.

[Paul Drawmer]

Years ago our house was heated by LPG. It was a very inefficient house - big stone place with little insulation, feeding a combi and a gas fired Aga. We had 2 pairs of 47kG cyls with an auto change over.

Pretty soon swapped to a bulk LPG tank, it saved a lot over the cost and inconvenience of the cylinder swapping.