Welcome to Lesson 7!
We are into Lesson Seven now: home heating basics. This is a very interesting and very important chapter. Let me warn you about one thing: this chapter has a lot of calculations, and in the entire course this is the most, I would say, calculationoriented chapter. So I want you to pay attention to this one.
Basically, if you have a house, you will be losing heat from various places like windows, like the ceiling, the roof, the walls, the doors, through the floor, everywhere. So in this chapter, we will be looking at how much heat loss occurs and by what means you will be losing it. Let's say we have this wonderful mansion and we want to keep the interior at, let's say, 70 degrees all the time. And we have a little furnace that puts out heat and that keeps the interior at 70 degrees even when outside it's, let's say, 10 degrees Fahrenheit. Heat always tends to get out. It can actually go through those solid walls, or if we have windows, it can go through windows or even the roof. And when you open doors and windows, air might leak in and out, so that's another way of losing heat. So there are several ways in which heat is lost to the outside.
How much heat the furnace has to put out to keep the temperature constantly at 70 degrees inside can easily be calculated or known when we know how much heat is escaping. If somehow, ideally, we can seal off this entire place without any heat loss, then once you bring this house to 70 degrees you can turn on the furnace and it will remain at 70 degrees for the rest of the season. But you and I both know that is not the case. So in this chapter, you're going to learn how much heat is escaping through various surfaces here. And obviously, whatever is escaping, that is the amount of energy that the furnace has to put out. Which means we have to buy energy and put it into the furnace in the form of fuel. So if we are losing a million BTUs like this through all these areas, we have to get a million BTUs made up from this furnace. And we also know that the furnaces are not 100% efficient, either. If we need to get 100,000 BTUs, or 1 million BTUs from the furnace, we cannot expect a furnace to put out if we put in 1 million BTUs. So if we want 1 million BTUs as output, obviously we have to put more in in the form of fuel. So to know how much fuel we have to put in, we have to know how much heat loss we actually have in the house.
So we will be looking at residential heat loss, how to calculate that, and in what ways we lose heat in this first chapter of Lesson Seven. We will understand the mechanisms of heat transfer and also calculate the heating degree days for a heating season, which is basically the number of degrees that we have to heat our air. If the outside temperature is low, obviously we have to heat our air to a higher temperature or higher number of degrees. That's more degrees of heating. So we will calculate how many degrees we have to heat per day and per season, and so on and so forth. And if we know that, we can calculate the heat loss from a solid wall. That is conduction heat loss. We will talk about conduction, convection, and radiation  those three mechanisms of heat loss.
And also, once we have a wall, not all walls are the same. Some walls resist more heat loss than the others. So we define a property of a wall, a property of a solid material that tells us how much the material resists the heat loss. That's called Rvalue. So we will understand and articulate the concept of Rvalue here. And we can also increase the Rvalue of a wall by increasing its thickness or by going to a different material, and so on. And if we were to have a wall with lower Rvalue, which means lower resistance, we would be losing more heat to the outside. And we would be requiring more heat or more fuel to heat that place. So we'll talk about the cost of various fuels for a given heat loss. Seeing 1 million BTUs that we lose, if we were to heat with natural gas to get that same 1 million BTUs, what would it cost? Or if we use electricity, what would it cost to get 1 million BTUs? Or if we use propane, what would it cost? But the heat loss is always 1 million BTUs. For the same amount of heat loss, which fuel happens to be cheaper fuel or more expensive fuel? That's what we will be determining here.
We will also understand that if we have to install more insulation, we will need to borrow more money. And if we borrow more money and put in more insulation, can we save enough through heat loss to pay back that money that we borrowed? That is payback period. You already know the concept. We will do some calculations to see whether it is wise to borrow money and put more into insulation. All right, that's basically part A here. And we will also look at part B, which is insulation and home heating fuels. And in this part, we will talk about various types of insulation materials and how we can improve a wall's performance by adding more and more layers to that wall. So if we have a wall that has four different materials together, we'll see that, for example, inside we would have drywall that we could paint easily. And behind the drywall we have the framework, like a wooden frame with wooden studs that are used for structural integrity. And between those studs you always pack some insulation material. And outside the insulation material is not visible because we'll have a plywood or sheathing outside. And even sheathing doesn't look good outside, so on top of that we put a siding, a vinyl siding or brick or whatever it is.
So when we have different materials together, one right behind the other, they will all together resist the heat loss. So we will calculate the heat loss resistivity or Rvalue of a wall that has different layers of insulation. And if we have that, we can find how much energy we can save or how we can cut the heat loss, et cetera. And also we will talk about the efficiencies, the furnaces, and how we can distribute the heat in the house into various rooms, et cetera, of different heating systems. We'll talk about that later on in the next chapter. So this is basically a calculationoriented and problembased kind of chapter or lesson. And if we have any more difficulties in this one, I also added on top of this the practice questions, a bunch of practice problems which explain you how to do numerical problems. For example, I have given here a bunch of problems, actually, using the formulas that we'll be looking at here for practice. There are a bunch of problems  about 30 problems or so.
Those of you who are comfortable with the material can do these problems yourselves and see if you got them correct by going to this answers page, where the same problems are given with answers. So you can actually look at whether you got the same answer or not. If you got it right, you are happy. If you don't, you may feel lost. If that's the case, what you do is click on this third one here, where for every problem we have a solution, actually, like audio that I'm speaking to you right now. I have made some movies again for each of these problems that will explain to you like a blackboard, or white board rather.
So there are a bunch of problems like this that you can look at. And most of the problems have solutions like this. So I've tried to make your life simpler. Lesson Seven is a twoweek lesson, which means you will have a quiz at the end of two weeks after the lesson is assigned. And you take the quiz at the end of the lesson.
Good luck.
Home Heating
Home heating is the single highest energy expense for a household.
 Energy spent for residential space heating accounts for about 10 percent of the total energy consumed in the United States.
 The average household consumes 92 million BTUs, and 46 percent of that is used for home heating.
 Average annual home heating expenses were $1,488 in 2001. Home energy use also accounted for 20 percent of the greenhouse gas emissions.
Therefore, reduction of energy consumption in home heating results in substantial monetary savings and reduction in air pollution. With appropriate improvements, average home heating costs can be reduced by 30 percent (i.e., about $500 a year).
Appliances  Percentage 

Space Heating  47% 
Electric Air Conditioning  8% 
Water Heating  17% 
Refrigerators  5% 
Other Appliances and Lighting  23% 
Lesson 7 Objectives
Upon completing this lesson, you will be able to:
 understand the mechanisms of heat transfer;
 calculate heating degree days for a heating season and articulate significance of Heating Degree Days (HDD);
 calculate heat loss from a home using conduction equation;
 understand the concept of Rvalue and its importance in home heating;
 compare the cost of various fuels for a given heat loss;
 understand the significance and be able to calculate the payback period.
Checklist for Lesson 7
Step  Activity  Access / Directions 

1  Read the online lesson  Lesson 7a  Residential Heat Loss Lesson 7b  Insulation and Home Heating Fuels 
2  Watch  Lesson 7  Guided Review (Flash movie). (A printable Review Sheet is also provided.) 
3  Read  Lesson 7  Questions for Review and Discussion. 
4  Review  Lesson 7  Resources (supplemental materials that are optional...but informative!) 
5  Complete  Lesson 7  StudyMate Activities. (You will obtain feedback for these exercises, but they will not count toward your final course grade.) 
6  Take  Lesson 7  Quiz (graded). The quiz is available in Canvas. 
7  Complete  Home Activity: Lighting

See the Calendar tab in Canvas for due dates/times.
Questions?
If you have any questions, please post them to the General Course Questions forum in located in the Discussions tab in Canvas. I will check that discussion forum daily to respond. While you are visiting the discussion board, feel free to post your own responses to questions posted by others  this way, you might help a classmate!