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* These tools are provided for educational purposes, only. Each home’s needs are unique, and there is no replacement for the advice of a trained technician.

Recent Blog Posts

In all this life, a little rain must fall.

Or so the song says. But what do you do when the rain lasts for a few weeks, the way it does in Richmond in the spring? Since we get a lot of questions from [...]

Consumer Checklist for Buying a Heat Pump

For most families, A Heat Pump is a major purchasing decision. The process of making this purchase can be stressful, confusing and difficult. So, to alleviate some of this stress, I wanted to create a [...]

Open Season on Dust Bunnies

In 1987, L. Jung with the Oak Ridge National Laboratory published a paper for the United States Department of energy (link: .pdf opens in new window) about the importance of air filters in refrigerant based [...]


(coming soon)

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Tools and Checklists

Your score was 0out of 15.

Any contractor scoring above a 12 is worth considering.

Time For Service Checklist

Your score is 0out of 25.

If your score was higher than 10, you should contact an HVAC professional to have a system diagnostic, and/or have your ducts cleaned.

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Frequently Asked HVAC Questions (FAQ)

Trane’s explanation is perhaps the most clear. “System efficiency is measured in SEER, which stands for Seasonal Energy Efficiency Ratio. Similar to miles per gallon in a car, SEER is a measure of the overall efficiency of a complete heating and cooling system on a seasonal basis. The higher the SEER, the greater the system’s energy efficiency[…].” This means that the higher the number, the more efficient your system is, and thus, you spend less to operate at a comfortable level.
All Heat Pumps in climates that get below 35 degrees need a supplemental heating source. This is generally accomplished by adding an electric heating coil to the unit. The added heating coil is also referred to as second-stage, emergency or back-up heat since it will kick in on cold days to help heat your home. Emergency Heat is when you use this secondary heat source without the use of your heat pump.
The short answer is, it depends. When various government agencies post these numbers, they generally are referring to an average. They also always include a statement about each home being different, and each home’s filter needs (even houses right next to each other) can be vastly different. To be on the safe side, you should CHECK your filter, at least once a month. The good news is that this is a simple visual check, and not terribly difficult to do. When dust builds up enough to restrict airflow, simply replace it.
The most frequently at fault things to check, first, are:

  1. Check that the unit is turned on.
  2. Check that the fuses, disconnects and breakers are turned on.
  3. Make sure the thermostat is set correctly.
  4. Check for any strange noises or smells.
The air temperature your system can create depends on the temperature of the air going into it. Generally speaking, the air coming out of the register should be 15°-20° below the temperature outside. Thus, if it’s 100 degrees outside, your system might only blow air at 80 or 85 degrees.

This is a gross oversimplification, though:

  • Assumes your unit is operating at it’s best efficiency
  • Assumes your unit has been recently serviced (or is fairly new)
  • Your unit is undamaged
  • Does not take into consideration variables like
    • humidity
    • whether the unit is in shade or direct sunlight
    • whether there are obstructions like plants around your outdoor unit
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Common HVAC Terms

The hourly ventilation rate divided by the volume of a space. For perfectly mixed air or laminar flow spaces, this is equal to the number of times per hour that the volume the space is exchanged by mechanical and natural ventilation. Also called air change rate or air exchange rate. Abbreviated ACH or ac/hr.
A central unit consisting of a blower, heating and cooling elements, filter racks or chamber, dampers, humidifier, and other central equipment in direct contact with the airflow. This does not include the ductwork through the building. Abbreviated AH or AHU.
Any of several units of energy (heat) in the HVAC industry, each slightly more than 1 kJ. One BTU is the energy required to raise one pound of water one degree Fahrenheit, but the many different types of BTU are based on different interpretations of this “definition”. In the United States the power of HVAC systems (the rate of cooling and dehumidifying or heating) is sometimes expressed in BTU/hour instead of watts. Abbreviated BTU or Btu.
A mechanical device for moving air or other gases.
A device that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This cooled liquid flows through pipes in a building and passes through coils in air handlers, fan-coil units, or other systems, cooling and usually dehumidifying the air in the building. Chillers are of two types; air-cooled or water-cooled. Air-cooled chillers are usually outside and consist of condenser coils cooled by fan-driven air. Water-cooled chillers are usually inside a building, and heat from these chillers is carried by recirculating water to a heat sink such as an outdoor cooling tower.
Equipment that performs heat transfer to air when mounted inside an air handling unit or ductwork. It is heated or cooled by electrical means or by circulating liquid or steam within it.
A component in the basic refrigeration cycle that ejects or removes heat from the system. The condenser is the hot side of an air conditioner or heat pump. Condensers are heat exchangers, and can transfer heat to air or to an intermediate fluid (such as water or an aqueous solution of ethylene glycol) to carry heat to a distant sink, such as ground (earth sink), a body of water, or air (as with cooling towers).
A system designed to provide a constant air flow. This term is applied to HVAC systems that have variable supply-air temperature but constant air flow rates. Most residential forced-air systems are small CAV systems with on/off control. Abbreviated CAV.
A device that controls the operation of part or all of a system. It may simply turn a device on and off, or it may more subtly modulate the set point of components. Most controllers are automatic but have user input such as temperature set points, e.g. a thermostat. Controls may be analog or digital.
A plate or gate placed in a duct to control air flow by increasing friction in the duct.
(Also delta T) a reference to a temperature difference. It is used to describe the difference in temperature of a heating or cooling medium as it enters and as it leaves a system.
Specialized housing that carries air flow to specific points in a room.
A dehumidifier is the equipment that extracts and removes humidity from the air. It works by cooling air to the point where water turns to liquid from vapor form and then the liquid is removed.
A diffuser is placed over ductwork, and it separates air with vanes going in differing directions. It evenly distributes air flow in the desired directions.
Dry bulb temperature is the temperature of air measured by a thermometer which is freely exposed to the air while it is shielded from radiation and moisture. It is usually thought of as air temperature, and it is the true thermodynamic temperature. It is a measurement of heat intensity independently of humidity and a dry bulb thermometer is used to measure it.
A component in the basic refrigeration cycle that absorbs or adds heat to the system. Evaporators can be used to absorb heat from air or from a liquid. The evaporator is the cold side of an air conditioner or heat pump.
A small terminal unit that is often composed of only a blower and a heating and/or cooling coil, as is often used in hotels, condominiums, or apartments. Abbreviated FCU.
A transfer of fluid volume per unit time.
Used to move fresh air. Abbreviated FAF.
An opening through which outside air is drawn into the building. This may be to replace air in the building that has been exhausted by the ventilation system, or to provide fresh air for combustion of fuel. Abbreviated FAI.
A component of an HVAC system that adds heat to air or an intermediate fluid by burning fuel (natural gas, oil, propane, butane, or other flammable substances) in a heat exchanger.
A gas furnace heat exchanger is responsible for the transfer of heat from inside the furnace into the air outside the furnace. The duct system then transfers this exchanged air to different rooms in the building or space.
A facing across a duct opening, often rectangular in shape, containing multiple parallel slots through which air may be delivered or withdrawn from a ventilated space. The grille directs the air flow in a particular direction and prevents the passage of large items.
A heating coil is the part of the system that conducts heat. It allows electricity to act as fire.
Terms for the amount of cooling (heat gain) or heating (heat loss) needed to maintain desired temperatures and humidities in controlled air. Regardless of how well-insulated and sealed a building is, buildings gain heat from sunlight, conduction through the walls, and internal heat sources such as people and electrical equipment. Buildings lose heat through conduction during cold weather. Engineers use heat load calculations to determine the HVAC needs of the space being cooled or heated.
A heat pump is a compressor that cycles hot or cold air. It is a device that is designed to move thermal energy in the opposite direction of heat flow by absorbing heat from a cold space which is released to a warmer space.
A liquid or gas used to transfer heat between two heat exchangers. An intermediate fluid is used when the hot and cold fluids are too bulky (such as air) or difficult to handle (such as halocarbon refrigerant) to directly transfer the heat.
1.  Components made of multiple smaller blades, sometimes adjustable, placed in ducts or duct entries to control the volume of air flow. When used inside of ducts, their function is similar to that of a damper, but they can be manufactured to fit larger openings than a single-piece damper.
2.  Blades in a rectangular frame placed in doors or walls to permit the movement of air.
A measure of the air temperature outside a building. The temperature and humidity of air inside and outside the building are used in enthalpy calculations to determine when outside air can be used for free heating or cooling. Abbreviated OAT.
An enclosed space inside a building or other structure, used for airflow. Often refers to the space between a dropped ceiling and the structural ceiling, or a raised floor and the hard floor. Distinct from ductwork as a plenum is part of the structure itself. Cable and piping within a plenum must be properly rated for its fire and smoke indices. See also: plenum chamber
A split system is the combination of an outdoor unit and an indoor unit. This is the most common type of system.
General term used to refer to the set or a subset of components that perform a specific HVAC function within a building.
An individual space or group of neighboring indoor spaces that the HVAC designer expects will have similar thermal loads. Building codes may require zoning to save energy in commercial buildings. Zones are defined in the building to reduce the number of HVAC subsystems, and thus initial cost. For example, for perimeter offices, rather than one zone for each office, all offices facing west can be combined into one zone. Small residences typically have only one conditioned thermal zone, plus unconditioned spaces such as garages, attics, and crawlspaces, and basements.
A thermostat is a system that monitors and regulates a heating or cooling system. It can be used to set the desired temperature at which it keeps the environment either heated or cooled.
A two-stage air conditioner is designed to operate on high and low settings during different weather conditions and seasons. The high setting is used during extreme weather, and the low setting is used during moderate weather. This type of air conditioner produces a balanced temperature and is in use for a longer period of time.
A thermostatic expansion valve is a piece of equipment that meters the flow of liquid refrigerant into the evaporator while measuring the vapor refrigerant leaving the evaporator. It thereby controls the superheating at the outlet of the evaporator.
An HVAC system that has a stable supply-air temperature, and varies the air flow rate to meet the temperature requirements. Compared to constant air volume systems, these systems conserve energy through lower fan speeds during times of lower temperature control demand. Most new commercial buildings have VAV systems. VAVs may be bypass type or pressure dependent. Pressure dependent type VAVs save energy while both types help in maintaining temperature of the zone that it feeds. Abbreviated VAV.
A zoning system sections a building or a space into zones which are controlled independently of each other. This is beneficial when different areas or rooms of a building have different temperatures as well as when the desired temperatures in different rooms are different. While temperature is usually controlled by different thermostats, some installations are done with dual-zone thermostats, allowing control of both zones from the same thermostat unit.
High Efficiency Particulate Absorbing filter. Like all filters, a HEPA filter traps particulates suspended in the air. HEPA filters are generally more efficient than standard filters, but also tend to cost more.