Your Home: Calculating Potential Energy Savings With the Home Heating Index
This is about taking a miles-per-gallon approach to calculating Home Heating Performance and Potential Home Energy Savings. I will cover the Home Heating Index formula that will allow you to evaluate your Energy Performance and Energy Saving Potential. By using this formula, you will have an indication of how much energy you may be able to save and how cost- effective those energy saving measures would be.
I compare this to calculating the miles-per-gallon of a vehicle. Raise your hand if you carry a small calculator in your car for figuring out miles-per-gallon. The calculator I use is one of the first solar powered calculators to hit the market. No battery backup, if I’m going to figure out how many miles-per-gallon my car got on the last tank of gas, I have to wait and fill up in the daylight.
Along with evaluating your rides energy performance, I also believe most everyone is interested in evaluating their homes energy performance. Is your home a 1 ton, four wheel drive, lifted pickup with oversize tires or is your home a three banger that came to America on a boat? Of course, a homes performance differs from a cars performance in one very important way, your home can’t be seen spinning out of a parking lot trying to impress the girls.
A home has to look good, but when it comes to performance, the less energy used the better. I have heard of people replacing their car engine with a larger, more powerful model and then bragging about all the fuel it consumes, but I have not heard of someone leaving the doors and windows open on their home and then bragging about their high electric bill.
Similar to miles-per-gallon in a car, a homes fuel consumption can be measured so judgment can be made concerning the benefit of installing energy efficient measures. When we’re talking about a home, instead of using miles-per-gallon, let’s use something the housing industry uses, let’s call it the Home Heating Index. The Heating Index provides a means of comparing homes of different size and different climates, and determining the cost-effectiveness of energy saving measures.
Home Energy Use
In heating climates where heating degree days ( use the furnace a lot ) out-number cooling degree days ( use the air conditioner a lot ), the calculation is called the Home Heating Index. And then, in a similar manner, when cooling degree days outnumber heating degree days, it’s called the Home Cooling Index.
Today, I am going to demonstrate just the Home Heating Index. The heating index has proven to be more beneficial and more accurate than the cooling index. Besides, it’s cold outside and time to be concerned about heating. ( Except for you folks in the far South, I will cover the Home Cooling Index another time.)
So, before proceeding with the adventures of climbing into the attic, exploring the underfloor, investigating appliance efficiency, and all the other things that takes place during an energy audit, you should pull out your favorite solar calculator and compute the Home Heating Index. With the Home Heating Index, you can usually correctly guess whether or not there is insulation in the attic space and if there is, whether more should be added.
Calculating The Home Heating Index:
The Home Heating Index is a calculation using Btu’s, square footage of living space, and heating degree days. This calculation can be completed whether the homes heating system is electric, gas, propane, wood, oil or candles.
The Home Heating Index for a wood heated home is a little more involved because Btu’s is calculated per cord per species. I think I will leave the wood burning for a time after I get a new calculator.
Let’s calculate the Home heating Index for a home with electric heat. This would include electric furnace, space and wall heaters, heat pump, radiant ceiling heat or floor heat, etc. For this calculation, we will assume this home has an electric water heater.
Step 1: Data from Electric Bill
Power Bill Energy Consumption
Grab your electric bill and look at the number of kilowatt hours your home used for the month of October. On my example home, the home used 1,640 kWh for the month. Now, look at the bar graph and select the month where electrical usage was the smallest. This is the month where your heating and cooling needs were the least, estimate the kilowatt hours used during this month. On my example home, during the month of September, about 680 kilowatt hours were used. This figure represents the electricity used for water heating, cooking, lights etc – everything other than heating and air conditioning.
Subtract 680 from 1,640 – the difference is 960 kWh. This is the energy used for heating during the month of October.
Step 2: Find the number of heated square feet in your home.
My example home is a two story home. There is 920 sq ft on the first floor and 800 sq ft on the second floor. Total sq ft = 1,720.
Might have to get out the old measuring tape, remember, square feet is length times the width.
Measure Your Home
Step 3: Determine the degree heating days for your location for the month of October.
Go to http://www.degreedays.net.
In the box labeled “weather station ID” type in your zip code and click on Station Search. A box will drop down, select the weather station nearest your home.
For Degree Day Type choose “Heating” and for Temperature Units choose either “Celsius” or “Fahrenheit”.
Leave the base temperature at 65 degrees and go ahead and check the box to include “Base Temperatures Nearby”.
For the Breakdown selection, choose “Monthly” and for the Period Covered, Choose “Last Twelve Months.”
Now your ready to click on “Generate Degree Days”.
At the top of your screen, a new box will appear that has a dotted wheel spinning around that indicates the Degree Heating days are being calculated. Wait until the wheel stops and the box says, “Your Degree Days Are Ready”, and then click on “Download Now”.
Open the chart that has been downloaded and choose the number of degree days for the month of October. For my sample home, the degree days are 344.
Step 4: Convert kilowatt hours into Btu’s.
The equation uses Btu’s, so we need to convert kWh into Btu’s. The following chart will allow us to make the conversion. If your working with natural gas or propane, those conversion numbers are given also.
1. One kilowatt hour of electricity equals 3,412 Btu’s.
2. One therm of natural gas equals 100,000 Btu’s
3. One gallon of propane equals about 91,450 Btu’
My example home used 960 kWh hours for heating which converts to: 960 times 3,412 equals 3,275,520 Btu’s.
Step 5: Plug the data into the Home Heating Index equation.
Length x width
To use the data we have collected to determine the Home Heating Index, the first thing we want to do is multiply the square feet by the heating degree days. Again, for my sample home, I would multiply 1,720 square feet by 344 heating degree days. Multiplied together they equal 591,680.
Now we need to divide the Btu’s by the 591,680. That would be 3,275,520 Btu’s divided by 591,680 to provide a Home Heating Index of 5.53. To evaluate the Home Heating Index number of 5.53, we use the following chart for fossil fuel heated homes and adjust the chart slightly lower for electrical heated homes.
Home Heating Index between 0 and 2; Airtight, super insulated, 90+ heating efficiency, Heat-recovery ventilator, small window area and high window r-value.
Between 2 and 4; Well insulated, low air leakage, efficient heating system, home labeled super good cents in USA or R-2000 in Canada.
Between 4 and 8; Better than average home with good insulation. Relative low air leakage, and better than average heating efficiency.
Between 8 and 13; Average home with average insulation, average air leakage, and average heating efficiency.
Between 13 and 18; Worse than average home, with little insulation, high air leakage, and worse than average heating efficiency.
Between 18 and 22+; Older homes with poor insulation, abundant air leakage, and very inefficient heating system.
(Home Heating Index Chart from Residential Energy by John Krigger)
By using the chart, we can see that my example home, with a Home Heating Index of 5.53, is not a high efficient home and not an energy hog. It is a better than average home that could benefit from additional insulation, additional air sealing and could benefit from a higher efficiency heating system. We can also look for additional energy savings through higher efficiency appliances and efficient lighting.
By using the Home Energy Index score, we can see that some additional weatherization retrofits can reduce energy consumption and be cost effective. If a home had a score of 1.5, it probably would not be cost effective to undertake weatherization retrofits. However, if the home had a score of 15, the home could benefit greatly from energy saving measures, both weatherization and higher efficiency appliances and those retrofits would certainly be cost-effective.
Unfortunately, the Home Heating Index is a little more difficult to calculate than miles-per-gallon of a vehicle. The implications, however, are even more important. Chances are you can’t do much to increase the miles-per-gallon of your favorite car, but the same is not true of your home, the chances are very good that you can increase the homes energy efficiency and save a lot of money that you can use to buy gas for the car.
Thanks for stopping by, hope to see you soon, but I won’t leave the light on for you…