Heating, Ventilation and Cooling Terminology
- System Capacity
- System capacity is a measurement of the total amount of heat or cooling the furnace, heat pump or air conditioner can produce in one hour. This amount is reported in Btu/hr on the nameplate of the equipment.
- Btu, short for British Thermal Unit is a unit of heat energy. One Btu is the amount of heat needed to raise the temperature of one pound of water 1°F. To get a rough idea of how much heat energy this is, the heat given off by burning one wooden kitchen match is approximately one Btu.
- The AFUE, or Annualized Fuel Utilization Efficiency, is the ratio of the total useful heat the gas furnace delivers to the house to the heat value of the fuel it consumes.
- Heat Pump
- A heat pump is basically an air conditioner with a reversible valve that allows it to operate in reverse, removing heat from the house and shunting it outdoors in the summer, and removing heat from outdoor air and shunting it into the house in the winter. Because heat pumps do not actually create heat—they just move it from one place to another—heat pumps are more efficient than other forms of heating.
- Coefficient of Performance, COP, is the ratio of energy input to heating capacity. This is the instantaneous measurement of the heating performance of the heat pump. It is comparable to knowing how many miles per gallon of gasoline a car gets when it is going full speed. You can find the COP on the nameplate of the heat pump.
- The Heating Seasonal Performance Factor, HSPF, is an efficiency rating for heat pumps. It is a measure of the average number of Btu of heat delivered for every Watt-hour of electricity used by the heat pump over the heating season. It takes into account variations due to weather conditions over a season. HSPF is comparable to knowing how many miles per gallon of gasoline a car got, averaged over the entire year.
- Energy Efficiency Ratio, EER, is the instantaneous measurement of the cooling efficiency of an air conditioner or heat pump. The higher the EER for an air conditioner or heat pump, the more efficient it is.
- The Seasonal Energy Efficiency Ratio, SEER, measures the average cooling efficiency, over the entire cooling season for an air conditioner or heat pump.
- Programmable Thermostat
- A thermostat with the ability to record different temperature settings for different times for heating and/or cooling equipment. Programmable thermostats can be electronic, or mechanical. Here is a sample schedule for both heating and cooling.
Time Heating Temp. Cooling Temp. Wake up 6:00 am - 9:00 am 72°F 75°F Leave 9:00 am - 5:30 pm 50°F 80°F Evenings 5:30 pm - 11:00 pm 68°F 75°F Sleep 11:00 pm - 6:00 am 50°F or off 78°F or off
- ACH stands for Air Changes per Hour. It is the number of times in one hour that the air in a house is completely replaced with outside air.
- The transfer of heat through a solid material.
- The transfer of heat by air flow.
- The transfer of heat directly from one surface to another (whithout the intermediate air acting as a transfer mechanism).
- Insulation is a substance that resists the transfer of heat, generally by incorporating small pockets of air. Insulation is rated in terms of thermal resistance, called R-value, which indicates the resistance to heat flow. The higher the R-value, the greater the insulating effectiveness.The R-value of thermal insulation depends on the type of material, its thickness and density. An excellent website covering insulation is the Department of Energy's Insulation Fact Sheet, produced by Oak Ridge National Laboratory.
- Radiant barrier
- Radiant barriers are thin sheets of highly reflective material, like aluminum, which reduce heat transfer from thermal radiation across the air space between the roof and the attic floor. Radiant barrier do nothing to prevent heat transfer by conduction or convection. An excellent website covering radiant barriers is the Department of Energy's Radiant Barrier Fact Sheet, produced by Oak Ridge National Laboratory.
- U-Value is a measurement of heat flow. The lower the U-value the more slowly the material transfers heat in and out of a home.
- R-value is a measurement of heat resistance. It is the inverse of the U-value, so the higher the R-value the better the insulation resists heat transfer. Many factors can affect the R-value of insulation, including the type of insulation, and the age of the insulation. To determine the R-value of the insulation in a house, first determine the type of insulation present, whether that insulation is new, and measure the depth of the insulation in inches. Look the insulation up on the table below, and multiply the R-value per inch by the number of inches present in the house.
R-values of Various Insulation Types Insulation Type R-value / inch
R-value / inch
Flexible Batts Fiberglass 2.6 3.2 Rockwool 3.1 3.6 Loose-Fill Redwood Bark 1.0 1.0 Cellulose 3.2 3.5 Fiberglass 2.0 2.4 Rockwool 2.4 2.9 Perlite 2.3 2.7 Vermiculite 2.0 2.4 Rigid Foam Boards Polystyrene, large curd, molded 4.0 Polystyrene, small curd, extruded 5.0 Polyurethane 6.0 Polyisocyanurate 8.0 Foam-in-Place Insulation Urethane 6.0 Foam Roofing 8.0
- Fiberglass is the most familiar type of insulation. It is spun from molten glass, and is pure white in its virgin state. Additives and binders often color the fiberglass, with pink and yellow being the most common. Fiberglass comes in rolls, batts and as loose insulation which is blown into place.
- Dirty grey, although the color can range through green and brown as well. Rockwool looks like old wool with dark flecks, and you can often find what looks like sand or small pebbles underneath the insulation. Rockwool is spun, like fiberglass, from the slag from refining metals. The debris that settles underneath the insulation is remnants of the slag, and condensed droplets of metal.
- Cellulose insulation is made from wastepaper, such as used newspaper and boxes. It is shredded into small particles, and chemicals providing resistance to fire and insects are added. Cellulose insulation is dusty and brown, with flat particles, on which you can frequently find legible print.
- Perlite is a white gravelly, yet extremely light material. It is the same material found in garden centers and used as part of potting mixtures. Perlite is no longer used as an insulating material, except for the occasional do-it-yourselfer, although it is not uncommon to find it in existing houses.
- Vermiculite is made from expanded mica, a mineral. Vermiculite used as insulation is identical to the material found in garden centers. Like perlite, it is generally no longer used for insulation, although again, it can still be found in existing houses.
- Rigid Boards
- Rigid boards are fibrous materials or plastic foams pressed or extruded into board-like forms. These provide thermal and acoustical insulation, strength with low weight, and coverage with few heat loss paths.
Window Efficiency Terminology
- Multiple layers of glazing
- Each layer of additional glazing improves the efficiency of a window, as dead air between panes prevents conduction of heat. Proper spacing of panes prevents convection loops from occuring between the window panes, further reducing heat loss.
- Tinted glazing
- Tinted glass and tinted window films reduce the amount of the sun's heat entering the building. The shading coefficient (SC) of a window is the amount by which the window reduces heat gain. The lower the shading coefficient, the less solar heat is admitted. New glazings reduce the heat gained by a house without reducing visibility as much as older tinted glass and films. Visible light transmittance (VLT) is the measure of the amount of light that comes through the window. Select a window with a VLT of 0.60 or higher.
- Frame material
- Wood, vinyl or fiberglass frames conduct less heat than aluminum frames, increasing window efficiency.
- Thermal break
- A material that doesn't transmit heat well, such as plastic, sandwiched inside the metal parts of the frame. This reduces the heat being transferred through the frame.Thermal breaks can be used in the spacer between panes of glass in multi-pane windows as well as in the main body of the frame.
- Low-E glazing
- A special window coating that helps prevent the warmth inside a house from escaping through the glass in the winter (pyrolitic). A variation (solar control) is designed to block heat from the summer sun. Low-E coating can reduce energy use by up to 35 percent.
- Gas fill
- An inert gas such as argon is used instead of air between the window panes. Inert gases have a much better insulation value than air.
- Condensation is the buildup of water droplets on a cold window pane. This can occur on the inside of single pane windows, and in between the panes of multiple pane windows. Condensation on single pane windows can damage windowsill and wall surfaces if extensive. Condensation between the panes of multiple pane windows indicates a problem with the seal between the panes.
- U-Value is a measurement of heat flow. The lower the U-value, the more slowly the window transfers heat in and out of a home.
- R-value is a measurement of heat resistance. It is the inverse of the U-value, so the higher the R-value the better the window resists heat transfer.
- More window terms from the Efficient Windows website.
Water Heater Terminology
- Peak-hour demand
- The maximum water usage, in gallons/hour, during the time of day when a family is likely to use the greatest amount of hot water.
- First-hour rating
- The ability of a water heater to meet peak-hour demands. It measures how much hot water the heater will deliver during a busy hour. The first-hour rating accounts for the effects of tank size, and how quickly cold water is heated.
- Standby losses
- Storage water heaters constantly loose heat by conduction through the walls of the tank, and through the first few feet of water pipes. To reduce standby losses, insulate the tank, the first two feet of the cold water inlet pipe, and the first three feet of the hot water outlet pipe.
- Energy Factor
- The efficiency of storage water heaters is indicated by its Energy Factor (EF), which is based on an average hot water consumption of 64 gallons/day. The higher the EF, the more efficient the water heater.
- Recovery efficiency
- How efficiently heat from the heat source is transferred to the water. The hot water tank, the recovery efficiency for a fuel-fired water heater must be 1 or less (it represents the fraction of energy in the fuel that actually makes it into the hot water). A reasonable value to use for recovery efficiency is 0.76. If you want the exact value for a particular model, you might have success with the AHRI Water Heater Directory. You can enter the exact manufacturer and model number and find out the exact specifications for that unit. Note that they provide recovery efficiency as %, but you need to divide by 100 to get a value between 0 and 1 to input to HES.
- Storage capacity
- The gallons of hot water a storage water heater can hold in the storage tank.
- Water Heater Temperature
- Water heaters have a thermostat which controls the temperature of the water. You can save money by lowering the temperature of a water heater to 120°F (about midway between the "Low" and "Medium" settings). If the home has a dishwasher without a heating element, they should leave their thermostat on the "Medium" setting (140°F).
- A lumen is the total amount of light emitted from a source. Lumens are typically used to rate the output of lamps.
- The lighting industry uses the term lamp to refer to the source of light, the light bulb itself, not the fixture where the light bulb is located.
- The physical item refered to as a "lamp," i.e., "table lamp" or "floor lamp," is called the fixture by the lighting industry.
- Incandescent lamp
- The most common source of light, glass bulbs with a filament inside. Approximately ninety percent of the energy consumed by an incandescent lamp is given off as heat rather than light.
- Fluorescent lamp
- Fluorescent lamps are up to five times more efficient than incandescent lamps, and last up to twenty times longer. They require a special fixture. Electronic ballast fluorescents are a new efficient improvement over the traditional magnetic ballast fluorescents. Fluorescent lamps are available as straight tubes, U-shaped tubes, circular tubes and compact fluorescent lamps.
- Compact Fluorescent Lamps
- These fluorescent lamps are small, and are designed to fit in regular lamp sockets. They do require a special fixture. The electronic ballast-based fluorescents are more efficient, and produce better light than the older magnetic ballast models.
- Color Rendition or CRI
- The CRI rates the ability of the bulb to render an object's true color when compared to sunlight. Look for lamps with a CRI of 80 or higher.
- Color Temperature or CCT
- The CCT refers to the color objects emit when heated to a certain temperature on the absolute temperature scale (Kelvin). The lower numbers correspond to reddish color and the higher to blue-white color. For color similar to incandescent lighting look for CCTs around 2700.
Lamp CRI CCT Incandescent 90-95 2700 Cool-White Fluorescent 62 4100 Warm-White Fluorescent 51 3000 Compact Fluorescent 82 2700 Halogen 95+ 2950