Annual heat loss kw vs. likely running costs - oil or gas?

[gordonspants]

We have an annual heatloss figure performed by our plumber, on a house with no mains gas - it has previously been heated by oil.
With our annual heat loss btu or kw figure, how easy is it to convert that to an annual kw per hour figure, so we can compare likely gas costs with likely oil costs?
Eg 300,000 Btu or 83 Kw would equate to roughly how many kwh of gas or litres of oil?
Then we can decide whether getting gas to the property is worthwhile in the short term, or will aid the sale - house is being restored to be sold in the next couple of years.
Many thanks for any advice

 

[big-all]

a kw off gas is around 3-5p[75-90% efficient] suspect its half the price off oil

 

[gordonspants]

So if our heat loss calc for radiator and boiler sizing is 83kw - house is old and big - how much will we spend per year heating it?
Is it as simple as 83000 x 3 pence?

 

[D_Hailsham]

We have an annual heatloss figure performed by our plumber

Are you sure it is an annual heat loss that he has given you? This would imply that he can predict how the outside temperature will change during the year.

Heating installations are always sized for the worst-case, e.g. an outside temperature of -1C or -3C. Maybe the installer has given you this figure.

 

[big-all]

much easier to find out how much heat you get from your oil and convert that to pence per kw

you also have standing charges with gas like electric or higher rate first units that = around £10 a month

 

[gordonspants]

Sorry, my mistake, this isn't annual loss, it's the figure you need to use to heat the house - ie rad sizing.
Big house - 3m ceilings, sash windows, one room alone is 17000 btu - one K2 rad in there might not do the job
But how do we get to an estimate of annual usage?
House has been semi-derelict for 40 years, only two or three rooms being in use and heated (elec portable heaters!!) - so any previous bills are useless.
It's impossible to use gshp as the heatloss is so horrendous, insulating walls is out as it's ornate lime render outside and similar fancy cornicing inside, and it has original sash windows that could be secondary glazed but would not make a huge difference. Loft is the only place we can insulate.
A stark choice between oil - not cheap to run - or gas - not cheap to install as we need a run of about 70 metres. Or electricity - and that is out straight away based on cost. Two big boilers will be needed whether gas or oil.
What I need to know is a rough annual running cost or kwH (<- note Hour in bold!) figure, if at all possible.
Then a decision can be made to go with gas or oil.
Can you assume 83kw X so many hours a day X so many months a year + a nominal amount for hot water? Or is there a better way to get to the figures?

 

[D_Hailsham]

Sorry, my mistake, this isn't annual loss, it's the figure you need to use to heat the house - ie rad sizing.
Big house - 3m ceilings, sash windows, one room alone is 17000 btu - one K2 rad in there might not do the job

It might be a good idea to compare the figure you have been given with that produced by the Whole House Boiler Size Calculator. From what you say each parameter will have to be set to the worst case, ie, solid walls, wood framed single glazed windows etc. You will probably need to measure the total window area as they tended to be more generous in the past.

 

[gordonspants]

Hi, have had a go at the whole house boiler calc using approx size and it gives a touch over 100kw.
But, how many kwh will the house consume in 12 months - is there any way to work that out?

 

[iwaters]

Estimating energy usage is quite a complex procedure as there are many factors. The acceptable methodology in the UK is called SAP. It takes into account the heat loss of the building fabric (and thus the heat transfer using average temperatures), infiltration and air changes, hot water demand and heating system effiency etc.

On an existing dwelling a number of factors are assumed because they can't be ascertained without an invasive inspection. Many factors such as heating patterns and temperatures are also assumed as the purpose of it is to compare dwellings like for like and so doesn't take into account how the dwelling is used. It is therefore not completely accurate.

I write software for this calculation for a living and it is complex stuff. If you are seriously interested in this question you will need someone to come and do an assessment. BREDEM is the original energy use model that SAP is based on and this is more tailored towards how the building is used and not just its fabric performance. You might find it hard to find someone who still offers this service.

 

[mickyg]

Your just gonna have to do some guessing. Here's a nice guess........
average uk household consumes around 16000kwh of gas a year, average uk house is at a guess around about the 16kw mark in heat loss. so you could say 1000kwh per kw a year. As i say its a wild guess, but at about £2500(3p/kwh) for gas use per year, i reckon thats not far wrong for 80kw.

 

[gordonspants]

Your just gonna have to do some guessing. Here's a nice guess........
average uk household consumes around 16000kwh of gas a year, average uk house is at a guess around about the 16kw mark in heat loss. so you could say 1000kwh per kw a year. As i say its a wild guess, but at about £2500(3p/kwh) for gas use per year, i reckon thats not far wrong for 80kw.

Sounds about right.
So, 83kw would be around 83000 kwh. Ouch.
Gas at 3p would be £2500.
Oil, at 65p + vat per litre each litre giving 11 kwh according to the internet would be just over £5000.
Ouch again.
Gas supply quote so far is just over £20k, so we need to do some sums.

Many thanks all

 

[big-all]

dig your own trench and save about half the connection charge assuming its on your land

 

[Malc]

Heating oil is 10.35 kWh / litre on top of that you need to allow for say 84% efficiency for a good non condensing oil boiler or 93% for a good condensing, giving 8.7 kWh/l or 9.6kWh/l. Oil is around 60p/l ex VAT. Gas is lot cheaper. In fact E7 night rate is cheaper than oil.

If your plumber has worked out the sizing he should have worked out the total house loss for a -1C outside temperature, then added an allowance for hot water heating and a some in hand to give a boiler size. What you want is the house loss. Then look up the degree days figure for where you live. With that you can work out a rough sum where a year is equivalent to N days at -1C and as you know the heat loss per day you can work out a rough annual consumption.

 

[iwaters]

When do you need to decide? If you want I can do some SAP calculations for you and override some of the defaults (No. occupants, potetinal heating patterns etc.) and do a couple of calcs with an oil boiler and one with gas.

It wont be completely accurate but should give some rough ideas as to cost. There is quite a bit of information I would need from you so if you are happy to collect that I am happy to do the calcs.

Let me know and I will send you the list of information required.

 

[D_Hailsham]

Hi, have had a go at the whole house boiler calc using approx size and it gives a touch over 100kw.

100kW!!! That's a small mansion or factory, not a house.

There's something wrong with the calculations. Can you post the data you entered?