What is an R-value?
An R-Value indicates insulating power or thermal resistance. The higher the R-value, the greater the insulating power. Higher R-values are more effective at maximizing your energy savings and comfort.
I would recommend that certain insulation products for R value refer to the product website. These R-values usually meet building code minimum standards, although even higher levels might prove to be a good long-term investment as energy costs increase.
Here's website for R Value Calculator for your needs: Just Type in your zip code.
Application Good Better Best
Attic R-30 R-38 R-38
Cathedral Ceiling R-19 R-30 R-38
Wall Cavity R-13 R-13 R-15
Floor R-11 R-13 R-19
Basement Wall R-11 R-13 R-15
Crawl Space Wall R-11 R-13 R-19
GOOD insulation levels will help provide basic protection from uncontrolled heat loss or heat gain through the home's exterior, allowing standard heating and cooling equipment to maintain a comfortable inside temperature. GOOD insulation levels generally correspond to U.S. Department of Energy recommendations for homes with relatively cheap sources of heating energy, such as natural gas. These R-values often meet local building code minimum standards, although in some areas codes might call for higher levels. These R-values should be considered the bare minimum for a modern building, and higher levels might prove to be a good investment as energy costs increase.
BETTER insulation levels provide increased protection from heat loss or heat gain through the home's exterior compared to lower insulation levels, resulting in reduced heating and cooling costs as well as a more comfortable inside environment and good sound control. BETTER insulation levels generally correspond to U.S. Department of Energy recommendations for homes with moderately priced sources of heating energy, such as heat pumps, fuel oil, or some natural gas. These R-values usually meet building code minimum standards, although even higher levels might prove to be a good long-term investment as energy costs increase.
BEST insulation levels provide maximum protection from heat loss or heat gain through the home's exterior, meaning low heating and cooling costs compared to other insulation packages, and often allowing smaller and cheaper furnaces and air conditioners to be used. Higher insulation also results in a comfortable, even-temperature inside environment and better isolation from annoying outside noise. BEST insulation levels generally correspond to U.S. Department of Energy recommendations for homes with relatively high priced sources of heating energy, such as all-electric houses. The high R-values apply to homes with other energy sources as well, to maximize comfort and protect against future energy cost increases. These levels will meet or exceed building code minimums in essentially all areas.
Matching insulation to your structure:
A home's structure often limits the insulation choices. For instance, 2"x 4" framed walls will accommodate R-11, R-13, or R-15 insulation batts, but 2"x 6" framed walls have room for R-19 or R-21 batts. (Rigid foam sheathing insulation can often be added outside the framing for additional R-value.) Likewise, a sloped cathedral style ceiling restricts the depth of insulation to R-30 or R-38 at most, while a flat ceiling with a full attic above it will have room for higher R-values of either batts or blowing wool. Ideally, the desired levels of insulation are considered during the design of the home.
What is Heat Loss?
- The typical home owner would like the inside of their house to be around 72∫ on the inside in the winter. This is called the Winter Inside Design Temperature. However, because it is cold outside, heat travels through the building envelope, the walls, windows and ceilings to the outside. This heat is lost by conduction. Also, cold winter air leaks into the house and warm air leaks out. This is called infiltration.
- There is a continuous movement of heat from the inside to the outside, which is measured in units called BTUs (British Thermal Units). The speed of the movement of heat is called the Heat Loss and is measured in BTUH, which means BTUs per Hour.
- If it is 72∫ inside the house and 52∫ outside then the 20∫ temperature differential will cause a certain number of BTUs to leave the house each hour, letís say that that number is 9,768 BTUH. The heat loss of this house at 52∫ is 9,768 BTUH. This means that your heating system needs to produce 9,768 BTUs each hour to keep the house at 72∫, when it is 52∫ outside.
- If it is even colder outside, then the house will lose more heat each hour, the heat loss will be higher. When selecting a heating system, at what outside temperature do you need to know the heat loss? Well, this of course depends on where you live, how cold your winters are. The temperature to use as an outside temperature is called the Winter Outside Design Temperature. This is the temperature, say 10∫ for instance, at which only 2 Ω% of the time is colder than 10∫. The heat loss of the house when calculated with an outside temperature of the Winter Outside Design Temperature is called the Design Heat Loss. Because the heat loss at any temperature other than the design temperature is not really a relevant number, we usually just say Heat Loss, rather than Design Heat Loss.
- The smaller the house the smaller heat losses.
- Adding insulation to the walls and ceiling (increasing R-value) slows the movement of heat, thus reducing heat loss.
- Reducing the inside temperature and moving to a warmer climate are two ways to reduce heat loss
- Better window frames, sealing cracks particularly around doors reduces infiltration as does better fireplace.
- Heat loss is made up of the heat lost by conduction through the building envelope and infiltration. Heat Gain occurs in the summer time. Heat Gain is made up of:
- heat gained by infiltration (warm outside air coming in, cool inside air leaking out)
- moisture gained by infiltration (moist outside air coming in, dryer air leaving)
- radiation from the sun, either direct or indirect, through windows, glass doors and skylights.
- heat and moisture given off by people.
- heat gained by conduction (through walls, windows, ceilings etc)
- given off by appliances
So you can see that heat gain is a little more complex. Notice that items 1 and 2 are directly related to the temperature of the outside air, just like their counterparts in winter heat loss calculations, but items 3, 4, 5 and 6 occur no matter what the outside temperature is.
Sensible Gain and Latent Gain
The heat gain associated with the temperature of the air is called the Sensible Heat Gain. The heat gain associated with the water in the air that leaks in due to infiltration and the water that evaporates from peoples skin as well as the moisture in their breath is called the Latent Heat Gain. If you add up the Sensible Gain and the Latent Gain you get the Total Heat Gain.
There is a Total Heat Gain at every outside design condition however the one of interest is the Total Design Heat Gain at the outside Summer Design Conditions.
The Summer Design Conditions consist of more than just the outside temperature. They consist of the Summer Design Temperature (only 2Ω % of time warmer than this) and Summer Moisture Content (measured in grains of water per pound of air, typical Houston 113, New York 98), Daily
Temperature Range (High, Medium or Low). The daily range is a measurement of how the temperature varies during the day. A high daily range means temperatures start cool in the morning, hot in midday and cool down at night. A high daily range will result in a lower heat gain than a low daily range where it starts out hot and stays hot all day.
Fortunately, with a computer program such as HVAC-Calc, the Summer Design Conditions and Winter Design Conditions for hundreds of cities are built in to the program. You select them once and then forget it.
There is also an additional unit of measurement that is used to describe the cooling capacity of air conditioners and that is the "Ton". One Ton is 12,000 BTU per hour (BTUH). It comes from the number of BTUís absorbed by a ton of ice melting in 24 hours. If you have a heat gain of 30,000 BTUH then you would need to remove 30,000 BTUH in order to keep the house at the indoor design temperature of say 75.
You could remove the 30,000 BTUs each hour by setting up some fans to blow the inside air over a mountain of ice, being sure to completely melt 2 Ω tons each day. Or you can install a 2 Ω ton air conditioner. Due to the difficulty of obtaining ice these days and the problems associated with drinking two and a half tons of ice water each day, most people will choose the 2 Ω ton air conditioner.