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electrical meter

How to calculate electric energy cost of common household items

Electricity from the utility company is delivered to your house and connects to a meter that measures the amount of electricity used. The electricity is sent through the meter and routed to the service panel which split the electricity into the circuits throughout the house to power the appliances, lights and wall outlets.

Each month the utility company collects this usage information from the meter to determine how much electricity to charge you for. Electrical power is measured in watts and is charged by the kilowatt-hour. Kilowatt-hour is simply how many 1000′s of watts are consumed per hour.

Let’s review all the terms you need to know to understand electrical cost.

Kilowatt is watts in units of 1000 (1 kilowatt = 1000 watts).

Watts (wattage) are calculated by multiplying the voltage by the current.  (Voltage x Current = Watts)

Kilowatt-hour (kWh) is how many 1000 watts are consumed in a one hour period.

Utility Rate is the cost per unit of electricity, measured per kWh (kilowatt-hour).


Calculating Electrical Energy Cost

To calculate energy cost the “kilowatts” are multiplied by “time in hours” x “utility rate”. The average utility rate for electricity in southern Iowa seems to range between 11 -14 cents per kWh. I’ll use 12 cents for the calculations.

Just a quick note on time, since the rate is based on hours, converting minutes to hours may be required for calculation purposes (Total usage time in minutes/60 = hours). For example: 45 minutes would equal .75 hours.


Let’s look at two examples for calculating energy cost:

Example 1 – 60 watt light bulb

The power consumed by the light bulb is 60 watts, or .06 kilowatts. Using the utility rate of 12 cents per kwh, each hour of use will cost slightly under 1 cent ($.0072) If the light bulb is on for 10 hours per day then the cost per day is 7 cents for that single bulb (.06kw x $.12 x 10 hours = $.07).  Considering how many light bulbs operate in a household it’s easy to see how the lighting cost per month can add up to a few dollars.

For example: I have 6 recessed 65-watt light bulbs in the kitchen that were on today for 16 hours – I like to hang out in the kitchen. The total wattage for all the light bulbs is 390 watts, or .39 kW. At 12 cents per kilowatt-hour, my cost for lighting the kitchen today is $.75. If that were a typical day, then my projected monthly cost would be $22.50.  Time to rethink leaving the lights on!


Example 2 – Space heater

The typical wattage of a space heater is 1500 watts. In kilowatts that equals 1.5 kW. Using the 12 cent kWh energy rate, the cost per hour for the heater is 18 cents. That doesn’t seem like much until you consider how that adds up over time.

Hours per day

Cost per day

Cost per Month

5 hours



10 hours



15 hours



20 hours




Use the below calculator to estimate electrical cost for your devices.


Calculating Amperage

Sometimes you need to know the ampere draw of a device, especially for determining the correct circuit size. If you know the wattage then you can determine ampere draw by dividing the wattage by the voltage.  For example, the 1500 watt heater plugged into a 120 volt circuit will draw 12.5 amps (1500/120 = 12.5).


If you would like assistance with determining the energy cost or ampere draw of various devices in your house, please contact us. We are happy to help.


Thank You,

David McGill
James McGill

Article written by Tim McGill, editor @ Tree Branch Publishing.

Dirty vs. Clean Air Filter

Why it’s important to replace your furnace air filter regularly.

Myth #1 – The main purpose of the furnace air filter is to keep the air clean in the home.

Myth #2 – You should buy the best filter available.

Both of these statements are false, or at minimum, only partially true.

First and foremost the purpose of a furnace filter is to protect the furnace from damage caused by dust, lint, or foreign objects that find a way into the airstream. Without filtering, these particles may cause damage to the furnace or, at a minimum, reduce the overall furnace efficiency; which will cost you more in energy. Filtering prevents dust and other particles from collecting on the heat exchanger causing excess heat inside the furnace; clogging up the air conditioning coil which reduces the air flow to the house and causes the blower to work harder; or collecting on the fan blade or blower motor causing it to overheat or have electrical damage. Repair of any of these items is expensive and can be avoided by ensuring a filter is in place and receives regular maintenance.

A secondary purpose of the air filter for many households is to improve the air quality by filtering out dust and other small particles, such as pollen.  However, the furnace is not designed as an air quality device so you may not be getting the benefits from a premium air filter that you are led to believe you’re getting. More on that topic in another article; this article is focused on the primary purpose of protecting the furnace.


A clogged filter may cause damage to your furnace.

Dirty vs. Clean Air Filter

Dirty vs. Clean Air Filter

So we established that a filter is needed to protect the furnace, however that same filter may actually cause damage if not maintained. When the air filter gets clogged with dust and other particles, the air flow through the filter is restricted and damage to the furnace and AC unit is likely.

  • Blower (fan) motor failure is common. The restricted air flow causes the blower motor to work harder. This reduces the life of the motor and may cause it to fail, i.e. burn-up. The “burn-up” simply means the motor overheats, which often results in permanent damage to the internal electrical windings or other components. Replacing a blower motor is a common repair and can cost $200 – $500 in parts and labor.
  • In summer months, restricted air flow through the AC cooling coils inside the furnace unit may cause the unit to drop below freezing temperature and “ice up”. When ice forms on the fins of the coil inside the furnace compartment, then the outside air unit must work harder; this may damage the compressor. When the ice melts inside the furnace compartment, the water may cause damage to electrical components or over longer periods of time cause metal to rust and deteriorate. In the best case scenario the iced-up coil can be fixed with a service call. If other components are damaged, then significantly higher repair costs can be expected.

If that’s not reason enough to maintain your air filter, consider the extra energy cost due to reduced efficiency when the air flow is restricted.

The good news is that these costly repairs can often be avoided by replacing, or cleaning if reusable type, your air filter on regular basis.  How often depends on the type of filter, the usage of the furnace, and the conditions in the home or business. More on how frequently to maintain your air filter is discussed later, first let’s talk about the different types of filters.


What type of air filter do I need?

While there are many different types and grades of filters available, most are effective at filtering larger particles, which is the primary concern for protecting the furnace. Refer to your furnace owner’s manual for the manufacturer’s recommendations for type and size of filter to use. The original furnace manufacturer is the best source of information on the type of filter to use as each furnace is designed for a given air flow and using the proper filter will help maintain that air flow. If you are not sure what your manufacturer recommends then contact us. We will evaluate your system and suggest a filter that will meet your needs.

As a general rule, for newer model furnaces the pleated filters work well at trapping the airborne particles. However, for an older style furnace, the pleated filters may be too restrictive on the air flow and thus a woven fiberglass filter is a better choice.


How often do I need to maintain the filter?

How often depends on the type of filter, the usage of the furnace, and the conditions in the home or business.

  • A higher efficiency filter will need replaced more often since they are better at trapping particles and tend to clog up faster.
  • During peak operating months the filter may need replaced more frequently than during months of lower usage. Remember to check your filter during summer months as well.
  • The environmental conditions of the home or business may require changing the filters more often. This is often true during a remodeling project when dust is more prevalent, or if you are sensitive to allergens.
  • Pet owners should consider changing filters more often as pet hair will tend to collect on the filter and cause it to clog up.

A general rule is check the filter monthly and replace (or clean if reusable) if needed.



If you need assistance with replacing your furnace filter, please contact us and we’ll be happy to send a service technician to you.

Thank you,

David McGill and James McGill

Article written by Tim McGill,editor @ Tree Branch Publishing.

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Licensed Contractor for HVAC and Refrigeration

Licensed by Iowa Plumbing & Mechanical Systems Board as required by Iowa Code.

Member of Refrigeration Service Engineer Society (RSES)

Licensed Electrical Contractor

Licensed by Iowa Department of Public Health - State Fire Marshal Division.

David McGill - Master Electrician
James McGill - Master Electrician

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Bonded and Insured according to requirements of Iowa Plumbing & Mechanical Systems Board.

Insured per requirements of Iowa Department of Public Health - 2 million

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When possible we like to support our local businesses.

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Lockridge - Centerville
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