1. Hot Water Usage Per Day. Input the value that you got from the water usage calculator or estimate it yourself.
2. Kerosene or LPG or Natural Gas.
The reason there are three calculators is because LPG gives off less heat than Kerosene per litre and Natural gas is charged per kWh.
3. Boiler efficiency.
If you don’t know just click on Boiler efficiency options and use the dropdown arrow as a guideline.
If you have an old Gas Oil boiler the efficiency ranges from 55-70% depending on its age and service history
If you have an Kerosene boiler the efficiency ranges from 60-70% depending on its age and service history.
If you have an gas fired LPG or Natural Gas boiler the efficiency ranges from 65-75% depending on its age and service history.
If you are not sure and bought into the house then choose the lowest value.
As an example, I bought into a house with a Waterford Stanley Super 80 cooker in the kitchen which has an efficiency rating of 54.9%
Assumptions: a litre of heating oil (kerosene 28 sec) burnt at 100% efficiency will release approximately 10.18KW of heat
a litre of heating (LPG) burnt at 100% efficiency will release approximately 7.15KW of heat
a litre of heating Gas OIL burnt at 100% efficiency will release approximately 10.55KW of heat
The calculations are based on raising your hot water temperature from your input starting temperature to 60˚C.
The calculator is not taking into account latent heat in your hot water tank, in other words
it is raising the temperature from your input starting temperature to 60˚C
If you are using Gas Oil use the kerosene button above as the heat values are within 0.4KW
4. Starting Temperature.
This will vary depending on your water source, water mains, well, ground temperature, header tank, etc.
So just stick a thermometer under the kitchen cold tap after running it for a few minutes or if you have clear access to your
cold water storage tank(header tank) measure the temperature there.
It will vary from winter to summer.
As an example, I am on a well and have a constant 9˚C, if you are on water mains just add a few degrees.
5. How many days per year do you use the burner v.s. immersion ?
The immersion is used usually in the summer say 6 months and the boiler over the winter say 6 months.
The times will vary depending on whether you live in Donegal or Wexford.
Note if you are using Natural Gas you probably don't use the immersion to heat your water so just put
zero in the immersion days and 365 in the boiler days. You can change this assumption if you wish.
6. Cost per litre or kWh.
Check your last bill and input the cost per litre or kWh.
In Feb. 2011 it was 82 cent (inc.Vat) per litre for kerosene so input 0.82.
Cost of Natural Gas is measured in kWh and was 5.5 cent (inc.Vat) per kWh so input 0.055
Don't forget to add vat. at 13.5% to your unit charge if you are checking your bill.
8. Quote for solar system less grant
When inputting your solar system installation quote subtract the grant amount if applicable.
If you are borrowing the money for the installation add the cost of the loan to your quote amount.
Try this online loan calculator to work out your cost of credit.
7. Fuel inflation estimate pa. This is very difficult to predict especially in these turbulent times.
Since 1947 to 2009 the price of a barrel of oil has risen on average by 8.28% pa.
So as a starting point put in 10% inflation. You can change this value.
But over the last 10 years it has risen at 38% pa.
The cost of 1000 litres of Kerosene was 430 euro in March 2009 and is 820 euro Feb. 2011 almost a 200% increase in two years.
So to work out your ROI the biggest variable will be fuel cost.
9. Solar efficiency or return.
This can vary for many reasons, panel orientation, shading, weather, etc. If you have to place panels facing east or west
or two panels one east and one west this will affect the efficiency. By efficiency in this case is the percentage of your
water that will be heated by the solar installation.
I have suggested between 50% to 70% but you can change this if you wish.