How can this be? Well, lets take the average home in a place with four seasons. Two of those seasons won’t require air conditioning or heat. So that means for only six months out of the year you will have an energy bill of even $500 a month. Much of this bill is a constant — for water heating and cooking and home lights. So the real energy cost is maybe $400 a month for each of those six months. So you have about $2,400 a year in heating and cooling energy costs. You can probably / theoretically save about a third of this cost of energy with new dual pane windows and a dual pane sliding glass door.
But then, if you ever open a door to enter or leave your home you will send torrents of hot / cold air from outside into the house. If you only open or close a door once a day — and don’t cook — then that 30% savings is probably fair. If you have a family and the door is opened several times a day — and you cook — then your savings are far less.
Lastly, the windows do open. If you actually open a window then you destroy the insulating properties of all the windows in all the rooms where air from this open window can flow.
But it gets worse.
Let’s pretend that you cook food in your home. Your stove has a fan. In fact, let’s profile for a moment, if you bought $20,000 in windows you probably have a spiffy kitchen top fan (or eat out of a pop top can of cold ravioli … the demographic goes either way here). Every time you turn on that fan you are pulling between 300 and 600 cubic feet of air per minute from outside the house to the inside.
Yes, you think that you are just blowing air out of the house with that fan. The problem is that the air you are blowing out must come from someplace. That air can’t come from just anyplace. It must, it will, come from outside.
If you don’t have an open window someplace then your kitchen fan will suck air down the chimney and coat the inside of your house with soot. It might pull the exhaust gasses from your furnace vent or water heater vent right into your home. It can even suck air into the house from the bathroom vent. You must have air flow. So every time you cook you are defeating the purpose of the dual pane windows.
Your savings will essentially be zero while you cook and for as long as it takes for the furnace or A/C unit to make up for the temperature change in the home caused by the inrush of outside air.
Do you ever use the toilet? Do you use the fan in the bathroom? There is another way that air is “exhausted” from the home but — again — that air has to come from someplace