Do you understand your energy bill? How do you know what you paid for electric versus gas? You can determine a lot about a home from the past 12 months of utility data. Most utilities provide access to this information online, take a couple minutes now to find out if yours does. The information is usually delivered as a spreadsheet or a similar common format.
Lets go through a monthly energy bill and calculate out what value to use when comparing our before and after measurements. Understanding how much we pay for energy and how costs are calculated will help us determine if we are saving energy, money or both. This exercise is for the average single family home without solar. We will post another article on how to calculate out what you are paying if you have solar.
First we need to determine what is on our energy bill. My utility provides both my gas and electric. I have a separate vendor for my water and sewer. Since I only have my gas and electric on one bill it makes it pretty simple to calculate out my costs. It will be up to you to analyze your bills and separate out any fees/taxes related to other services provided by your utility.
For this example we are going to analyze my energy bill for July 2022. My total charges were $155.50, $6.96 for 3 therms of gas, $77.93 for 351 kWh Electric delivery, and $70.61 for the same 351 kWh Community Choice Aggregator Electric Generation. I am going to keep this as simple as possible and use straight arithmetic. Get out your abacus and count with me:
- Natural Gas: $6.96 / 3 Therms= $2.32 per Therm
- Electric : $148.54 / 351 kWh = $0.42 per kWh
So I am going to use $0.42 per kWh for my electricity costs and $2.32 per Therm for my gas costs in my examples throughout this site. On my energy bill my average cost is listed as $0.39 per kWh which is not counting some of the fees, we will do a deeper dive on what goes into your energy costs but this should be enough to start calculating how much an improvement may save and if it is worth the investment.
The home in this example was originally built in 1959 and is undergoing a series of energy upgrades spurred by years of deferred maintenance by the previous owner. It is 1350 square feet 3 bedroom 2 bath home with a tankless gas water heater and a ductless one ton heat pump. The plumbing system has been completely replaced from the farthest outlet to the street. The home has an advanced roof and recently upgraded electrical and gas system.
To figure out my energy intensity per square foot we first need to convert our gas and electric quantities into a similar unit. I use a simple converter online to convert my gas use in therms to kilo-Watt-hours= 1 thrm = 29.329 kWh so our three therms of gas use converts to 88 kWh. Add this 88 to our 351 to get 439 kWh. Divide this by our square footage to get an energy use intensity of 0.33 kWh/Sq Ft. Converting this to BTU’s per square foot we get 1126 BTU’s/Sq Ft.
