The power of the suction motor is one of the most important aspects regarding the performance of a vacuum cleaner. It is the suction motor which takes the electrical power from the power source and converts it into mechanical power in the form of suction with air flow. Rating the motor for its ability to produce suction with air flow is one of the most misrepresented and misunderstood aspects of vacuum cleaner technology. This confusion has been accentuated by many manufacturers in their attempt to make their products appear superior to others. One company which does a huge amount of advertising even claims its brand "vacuum cleaner doesn't loose its suction - ever." However, a major consumer magazine states that its cleaning ability is only mediocre to start with. This article is intended to assist you in cutting through the confusion of power ratings and to help you understand how these ratings apply to actual cleaning effectiveness.
For over thirty years the most common power rating used for suction motors in canister and power team type vacuum cleaners was Peak Horse Power (PHP) while upright types were usually rated by Amperage (amps) drawn from the power source. Over the past few years the peak horse power rating has largely been replaced with amperage ratings or Wattage (watts) ratings on many canister and power team types. Some manufacturers are using a different rating called Air Watts in an effort to rate the output power of the vacuum cleaner instead of the input power drawn from the power source. The actual Sealed Suction produced by the suction motor as rated in inches of water lift is a very good indication of the performance of the motor. Air Flow in Cubic Feet per Minute (CFM) is sometimes rated as well. The ability to efficiently convert the input power to output power varies substantially in the vacuum cleaner industry.
Amperage Ratings
The amperage rating shows the maximum amount of electrical current which normally flows through the vacuum cleaner's electrical system. This is the sum of the amounts flowing through the suction motor, power nozzle motor, light bulb and electronic components. The suction motor accounts for most of the current flow while the power nozzle motor typically has 1.5 amps flowing through it. A rating of 12 amps is the maximum permitted for any appliance which plugs into a standard household electrical outlet. If you see a rating larger than twelve on a vacuum cleaner, it is probably a Cleaning Performance Rating, not Amps! The amperage rating by itself is not a power rating but is part of the formula for computing the input power of the motor as described in the section about Wattage. Since the voltage in a standard household electrical outlet is always the same, amperage can be easily used when comparing the input power of various motors.
Peak Horse Power
Peak Horse Power is an exaggerated rating of the output of a vacuum cleaner suction motor. Most motors used in power tools are rated in actual Horse Power in which one horse power equals 746 watts. Horsepower can also be derived from the formula in which one horse power equals 550 foot-pounds of work per second. The rating for Peak Horse Power is found by taking the suction motor without its fans and adding as much load as possible without burning it out and then measuring the horse power using the formula which is based on torque per second. This results in a rating that is many times higher than the actual horse power of the motor. Keep in mind also that this motor rating does not take into account the number of fans which the motor is driving. An example of this is that a 4.0 PHP motor with two fans produces about 33% more suction than a 4.0 PHP motor with only one fan.
Around 1975 the Vacuum Cleaner Manufacturers Association established a power rating based on the motor power as measured in its normal operating range. This resulted in a much more realistic power rating in the range of 0.7 to 1.25 horse power. For a short time some manufacturers showed both horse power rating but today the VCMA rating has vanished since it is so much lower than the peak horse power rating. The peak horse power rating have mostly dissapeared as well in recent years.
Wattage
Wattage ratings are obtained by multiplying the Amperage drawn from the power source by the Voltage (typically 103 to 120 volts) of the power source. It is a measure of the input power of the motor. Wattage ratings seem to be used by some manufacturers to make it harder and more confusing when trying to compare their products to the competing ones which use Amperage Ratings.
Air Watts
Some manufactures have been using the Air Watts specification in an effort to rate the output power of the vacuum cleaner instead of its input power. This rating is mostly used for rating the power unit in a central vacuum system. It is based on suction with air flow at the unit itself so it is affected by the suction produced by the suction motor as well as the internal resistance to air flow. The suction and air flow are measured with the air flow being restricted by a two inch opening. The formula for Air Watts is as follows: (Air Flow * Vacuum)/8.5 = Air Watts. The Air flow is in Cubic Feet per Minute (CFM) and the Vacuum is in Inches of Water Lift. Care should be taken to not confuse this suction with air flow rating with the sealed suction rating (no air flow) which is about four times higher.
Keep in mind that the air watts rating does not necessarily reflect the actual air flow in the complete system in normal use. In addition to the resistance within the power unit, there is resistance caused by air turbulence in the hose and tubing, restriction where the cleaning nozzle contacts the floor, as well as increased resistance within the filtering system as the unit fills with dirt. Therefore it is important to compare the Sealed Suction along with the air watts when comparing canisters, power teams, and central vacuum systems.
Sealed Suction
The sealed suction of a vacuum cleaner as rated in inches of water lift is a good indication of how well it will perform, especially when comparing systems with higher resistance to the air flow. The air flow is proportional to the amount of suction produced by the motor and inversely proportional to the total resistance to air flow within the complete system. Therefore, if everything else is equal, the more suction produced by the motor, the better the performance of the system. The sealed suction rating is somewhat greater than the suction normally produced when operating with air flow. It indicates the maximum suction which can be produced by the motor as described in the section about the load on the suction motor. Since the sealed suction rating is measured with absolutely no air flow, it is not affected by the resistance to air flow within the system. If there are no leaks within the system, the sealed suction as measured on a gauge will be the same at the cleaning nozzle as it is at the suction motor. Even if the filter system is extremely restrictive, the sealed suction will not be affected by it. Alternately, when air flow is present, the actual suction will decrease as resistance to the air flow increases between the suction motor and the point where it is measured.
Air Flow
You will sometimes see the Air Flow in Cubic Feet Per Minute (CFM) rated for a vacuum cleaner. While the air flow rating is not a direct rating of the power of the suction motor, it is affected by its suction. The air flow rating is typically obtained by measuring the air flow through the power unit with the restriction of a 2" opening simulating resistance to air flow. The air flow is proportional to the amount of suction produced by the motor and inversely proportional to the total resistance to air flow within the complete system. There are many variables which affect the actual air flow in a system which are not reflected in the air flow rating. In addition to the resistance within the power unit, there is resistance caused by air turbulence in the hose and tubing, restriction where the cleaning nozzle contacts the floor, as well as increased resistance within the filtering system as the unit fills with dirt. Therefore it is important to compare the sealed suction along with the air flow when comparing canisters, power teams, and central vacuum systems.
Air flow through a system is a very important performance aspect in that it, coupled with agitation from brushing and beating action, does the work of picking up the dirt. Unfortunately, due to the many variations in the resistance to air flow which are not considered when rating the air flow, it may not be a very good measure of system performance with normal use.
Summary
The ability to efficiently convert the input power to output power varies substantially in the vacuum cleaner industry. It is often assumed that the greater the input power the greater the cleaning effectiveness but this is not always the case. The number of fans in a suction motor can affect actual vacuum cleaner performance. Some central vacuum systems like the Hayden SuperVacs actually have three fans pulling in series to provide plenty of suction to pull the air through the long tubing runs. However, some newer motor designs, like the Miele Vortex Motor used in all their vacuums, produce high suction and air flow amounts with only one fan. To learn more about motor and fan designs and how they affect vacuum cleaner performance and durability, see our articles on Suction Motor Design & Operation and Fan or Impeller Types & Performance.
The power of the suction motor is an important aspect to consider when comparing various vacuum cleaners but it isn't the only critical performance factor. Other important performance aspects of the vacuum cleaner system are the Effects of Brushing Action, the Air Flow through the System, the Filtration Efficiency - HEPA, ULPA, etc. and the Dustbag Performance and Filtration Efficiency.
It is the velocity of the air flow where the nozzle contacts the surface being cleaned, coupled with agitation from brushing and beating action, that determines how well the dirt is picked up. The portion of power applied to produce air flow verses that applied to the agitation varies with different vacuum cleaner styles and manufacturers.
When choosing a vacuum cleaner, you also want to learn about Identifying Durable Designs & Construction and how to Match Your Tasks and Cleaning Style. A knowledgeable sales person like those at Ristenbatt Vacuum Cleaner Service can help you determine which vacuum cleaner will be the best for your particular cleaning needs and preferences.
Next Vacuum Performance Aspect: Air Flow Through the Vacuum Cleaner System