Gas Boiler Consumption calculation

Morkin

Hi Folks,

We've a Ferroli gas boiler (2 years old) in a detached house in an estate supplied by piped Calor Gas (so not the same as Bord gas in supply type or cost).

We received a bill today for January of 550 euro. The boiler is on between 5 an 6 hours a day and before I give Calor a bell I want to calculate the hourly consumption of the boiler when on to max. temp. just to give me a sanity check.

We also have a gas hob used daily but this shouldn't affect things too much.

Can someone give me such a formula and also whether or not a bill of this size is normal (Calor prices are up over 50% in last year).

Thanks,

M.

10-10-20

I don't think it's as easy as that.
Heat created = energy used.
Unless the boiler is running inefficiently, you'll have to look at additional insulation and a lowering of the temperature in the residence.

311

You'll need the calorific value of the gas your using.
Also.
Measure the units your using if you have any way of doing that. I'm not familiar with calor installations ,but I presume if your billed ,you have a meter.

Reyman

If that 550 Euros is for one month at 5-6 hours running a day you have something seriously wrong.

I can't see how it could be more than 100-150 Euros for a month assuming the normal 7-8 radiators are on

youtheman

Two things you need to know:
The heat input to your boiler. Mine is 25 kw (kilowatts). There will be a data plate on your boiler with this information.
The price of gas, used to be sold as Volume but now sold in Volume and Energy (kwH kilowatt hours is an energy term). If you only know the volume them you have to know the calorifice value to convert to energy. But if they tell you the energy value then you're sorted.

Take mine for example.
Boiler is 25 kw
Last bill is 195.15 euros (ex VAT) for 4328 KWH.

So 4328/25 = 173.12 hours (at full rating).
195.15/173.12 = 1.13 euros (ex VAT) per hour at full rating

So if you were paying the same as me in energy, your bill should be 30 days x 5 hours/per day x 1.13 euros per hour = 170 euros.

Looks like you're being screwed.

311

You cannot compare one persons supply with another ,there are different calorific values for gases.

You might be getting charged a high rate for a lower calorific value.

youtheman

Yes you can. That is why you look for the Energy Term (kwh). This incorporates the calorific value in the equation.

311

youtheman wrote: »

Yes you can. That is why you look for the Energy Term (kwh). This incorporates the calorific value in the equation.

So whats the average rating for a 12+ Kw gas boiler ?

youtheman

Your boiler data plate should have two important figures:
Heat Input
Heat Output
So for example if it has a heat Input of 25 kw and a heat output of 24 kw this means that is is 24/25 or 96 % efficiency.

So if you run it at full load for one hour it will use 25 kwh, two hours its 50 kwh, and so on.

As I said before Natural gas was originally sold in volume terms as the calorific value was constant. Then we laid an interconnector to Europe and we are getting a mixuture of gas from all over the world. So they then starter to sell it in energy terms. The producer measures the volume, and the calorific value, and converts it into an energy term. So Joe Bloggs in Cork could be burning gas from the Kinsale Head Gas Field, and Mary in Dublin gas from Russia. They don't give a damn about the calorific value as this has been eliminated when they converted volume to energy.

My example was 1.13 per hour for a 25 kw boiler, a 12 kw boiler will be approximately half that.

Am I making sense?.

311

Your confusing me with someone who doesn't use one of these


Everyday to rate gas appliances and check for leaks

youtheman

Had another look at me Bord Gais bill. Its 4.509 cent per kilowatt hour (kwh).

So a 12 kw boiler will be 54 cent per hour (plus VAT).

youtheman

Your picture is a manometer which measures pressure. Still don't get your point.

311

youtheman wrote: »

Your picture is a manometer which measures pressure. Still don't get your point.

Sorry I'm lost

youtheman

I tried my best. Better leave it there so.

311

Morkin wrote: »

Hi Folks,

We've a Ferroli gas boiler (2 years old) in a detached house in an estate supplied by piped Calor Gas (so not the same as Bord gas in supply type or cost).

We received a bill today for January of 550 euro. The boiler is on between 5 an 6 hours a day and before I give Calor a bell I want to calculate the hourly consumption of the boiler when on to max. temp. just to give me a sanity check.

We also have a gas hob used daily but this shouldn't affect things too much.

Can someone give me such a formula and also whether or not a bill of this size is normal (Calor prices are up over 50% in last year).

Thanks,

M.

Sorry Morkin , make sure your boiler is properly rated.

10-10-20

Just to put my spoke in here.... the maths supplied by youtheman above will only provide you with the maximum output of the boiler per time period (hour/day...).
If you have a newer boiler and a room thermostat, it will modulate and power-down over the course of a run-period, so unless you know, through measurement, what gas has been consumed you can't determine the actual usage in €€!

Hence I replied to say "it's not as easy as that"...

Morkin

Thanks for the replies so far - some more info.

The estate has a tank and each house has a meter and bills arrive with units of cubic meters of LPG with a current unit price of 2.25 euro ex. vat per unit.

I've a pending request on how I get from there to the kwh value I'm used to seeing in Bord Gais (natural gas) bills.

The boiler is an Optimax 25 and the spec sheet (outcrop attached) says 25.2kW as the max heating power and a max flow rate for LPG of 1.96kg/hr. So i'm assuming it's a 25Kw boiler but am confused by the kg/h spec.

I'm going to monitor the meter with boiler set to max for 1 hour and see what it says but I'd like the backup of some old fashioned sums as well.

As always, input appreciated.

Rgds,

M.

youtheman

The following is taken from the Calorgas FAQ web site:
Q : What is the calorific value of LPG?
A : Butane = 7.8 kWH/Litre (of liquid)Propane = 7.1 kWH/Litre (of liquid)

* The price you quoted didn’t make sense when I did the figures so I rang Calorgas and they quoted me a price of 66.56 cent per litre (not sure if it’s Butane or Propane), ex.VAT.

So (cent/litre)/(khw/litre) = cent/kwh
So 66.56/7.8 = 8.53 cent per kwh for Butane (I’m assuming it’s Butane, Propane will be slightly dearer to the ration of 7.8/7.1).

As per my previous example Bord Gais are charging me 4.509 cent per Kilowat Hour. This is the cost of a unit of energy, and will be independent what type of a house you have, air temp, calorific value, etc. You’re comparing ‘apples with apples’.

If you run your 25 kw boiler at 5 hour per day AT FULL LOAD it will cost you 25 x 5 x 8.53 = €10.66 per day.

So Calorgas appears to be twice the cost of Natural Gas in Energy Terms.

As per previous comments, if it’s on for 5 hours then it will be unlikely to be on full load for this duration, but the above calculation at least gives you a ‘worst case’ scenario.

* 66.56 cent litre is €665.6 per cubic metre, so the €2.25 you quoted seem ridiculously low. If the price they quoted me over the phone is wrong, then all my calculations and assumptions above are also wrong.

Morkin

Thanks for the info.

The latest bill I received shows a unit price of 2.2151 ext VAT where units are cubic meters. I've a pending email query to Calor on what the conversion ratio is.

Just did a reading myself on the meter and it's used 90 units in the last eleven days - at that rate it's costing almost 21 euro per day to head a 2000sq. ft. house (5 - 6 hours per day at about 3/4 on the dial on front of boiler).

There is no apparent leak as the meter stays steady when boiler is off and there is no smell. I'm going to see what the hourly consumption is tonight.

Calor themselves have said that it should be about half what it currently is and are sending the local supervisor out next week.

I'll keep this updated for any who are interested.

M.

Morkin

Just came across the following:

http://forum.onlineconversion.com/showthread.php?t=7127

which says the 1 cubic meter of propane as liquid is between 277 and 270 litres of propane as gas.

Taking 7.1 kWH/Litre (of liquid) and a cubic meter unit price of 2.2151 ex VAT

I'm getting 270x7.1 = 1925 kWH/m~ and the kWH price is 2.2151/1925 = .115c?

You're right youtheman - makes no sense unless I'm getting messed up by litres of gas versus litres of liquid. The bill doesn;t say if they are talking about cubic metres of gas or liquid but do state the following in small print:

Bulk road tankers are equipped to read in litres correct at 16 degrees C. for what that's worth.

M.

311

Morkin ,your boiler has a modulating gas valve. From 7KW-25KW.

The best time to take a reading is about 20 minutes after you've turned on the system from cold ,i.e first thing in the morning.

Make sure all the thermostats on the walls and in the hotpress are turned up all the way.
Take a reading at the meter for 15 minutes.
Obviously multiplying by four gives you an hour .

Taking a reading like this ,will give you a much better idea of your usage.

youtheman

Morkin,

The amount of 'matter' in a liquid depends on the volume. The amount of matter in a gas depends on the volume AND the pressure (cause it's compressible). The conversion factor you quoted does not state what the pressure is (it might be atmospheric). So you can't use it.

If you're talking to Calor gas you want only one piece of information "what is the cost of a kilowat hour of gas ". You don't have to worry about whether it's liquid volume, gas volume, pressure, calorific value etc.

You know you boiler is rated at 25 kw MAX. If you know what the cost of fuel is in kilowat hours then you can calculate what the MAX cost will be. You can then use a 'rule of thumb' to estimate the actual cost.

JamesM

Your most economical move would be to spend about Euro3000.00 and get in a kerosene boiler. I am afraid that "Gas in a tank" is the least economical heating system available - or so I'm told
Jim.

Morkin

Thanks to all once again.

I've had the boiler on over the w/e with the thermo on the front set to ~3/4 and both zone thermos in the house at ~24C and I've checked the meter after each hour. Consumption is ~.8 (cubic meters) per hour which at current prices is €1.77 ex VAT.

Looks like an oil boiler and tank will pay me back in a few years.

So 1) any suggestions on a good one and 2) are the figures on the SEI site accurate and 3) is oil my only viable alternative for paying for itself in a reasonable timeframe?

Thanks,

M.

PS - Why the eff do Calor meter in cubic meters and not provide a simple conversion or if there isn't an simple answer then make some effort to aid comparison (other than just a kWh figure that one takes in good faith)

Morkin

Got the following,

The conversion you require is 1 cubic metre of Propane Vapour at 37mbar
or standard pressure = 3.652 litres of propane liquid.
1 litre of propane liquid = 7.1 kW

Then 1 cubic meter gives 25.9292 kW (at std press.) and my boiler is 25kWh max so very roughly one hour of boiler at max is one unit of propane.

I'm now confused as to how I've used 90 units in the 11 days between my last reading and doing my own reading on foot of the huge bill for January.

Anyhow, currently pricing an oil boiler replacement.

Thanks folks,

M.

simon_24

hi everybody,

i'm after recently getting a bill myself in the post from calor gas for 3 months - €689 for 2 and a half months!! I was disgusted, especially as no other bill has ever been this big, and I live in a 3 bed semi! Has anyone any ideas on how this could be, only using the gas for 6-7 hours over 24hr, according to them my average consumption is 3.6cubic meters a day; does anyone know any other cheap economical ways of heating said house?