Guides

Plain-language answers to the home-energy questions people actually search. Each guide links to a calculator that shows its work.

Wall vs Attic Insulation: Where Should You Add R-Value First?

In almost every house the attic comes first. It is the cheapest, most accessible place to add R-value. Here is why, and when walls matter.

Is Adding Attic Insulation Worth It? R-Value and Payback

Adding attic insulation is usually worth it if your attic is under about R-30, with payback in a few years. Here is how R-value and payback actually work.

What Size Generator for a Refrigerator and Furnace?

A fridge, a gas furnace blower, and some lights usually run on a 3,500 to 5,000 watt generator once you account for startup surge. Here is the math.

What Size Generator Do I Need to Run My House?

Most homes need a 5,000 to 7,500 watt generator for essentials, or 10,000 watts and up to run nearly everything. Here is how to land on your number.

How Much Does Central Air Conditioning Cost to Run?

A typical 3 ton central AC pulls about 3,000 to 3,500 watts and costs roughly 50 to 60 cents per hour, around 90 to 180 dollars a month in peak summer.

How Much Does It Cost to Run a Space Heater?

A 1,500 watt space heater costs about 25 cents per hour at the U.S. average electricity rate, roughly 2 dollars a day and 60 dollars a month for typical use.

Is My Furnace Oversized? The Signs of Short Cycling

Yes, you can tell if your furnace is oversized. Watch for short run cycles, frequent on and off, hot and cold swings, uneven rooms, and higher bills.

How Many Watts Does a Refrigerator Use?

A typical home refrigerator draws about 100 to 250 running watts and 700 to 1,200 watts at startup. Here is what that costs to run and how to find your own number.

What Size Mini-Split Do I Need for One Room?

For one room, figure about 20 BTU per square foot of cooling, so a 400 sq ft room lands near a 9,000 BTU head. Here is the table and the adjustments.

What Size Air Conditioner Do I Need? (Tons by Square Foot)

A quick rule of thumb is about 20 BTU per square foot, so a 1,500 sq ft home needs roughly 2.5 tons. Here is how to size it right and avoid going too big.

What Size Furnace Do I Need for a 1,500 Sq Ft House?

A 1,500 sq ft home usually needs a furnace in the 45,000 to 90,000 BTU range, depending on climate and insulation. Here is how to land on your number.

How Many BTUs Do I Need to Heat a Garage?

A typical 2-car garage of about 400 to 600 sq ft usually needs 30,000 to 60,000 BTU, depending on climate and insulation. Here is how to land on your number.

What Size Furnace Do I Need for a 2,000 Sq Ft House?

A 2,000 sq ft home usually needs a furnace in the 60,000 to 120,000 BTU range, set mostly by climate and insulation. Here is how to find your number.