Welcome to Heating 101. Once you understand this easy lesson, you'll know more about how energy is converted from a fuel (gas or oil) to your living space. I dare might add that you'll know more than a fair amount of heating contractors who simply know how to hook up a furnace and flip the "on" switch.
The heating appliance (boiler or furnace, usually) makes the heat, and the heating system delivers it (baseboard, duct, radiators, radiant floors). Heating Contractor trainer Dan Holohan uses the "train" analogy. The heat gets on the train at the furnace, and the heat hops off the train at the various rooms. Now, the train station is happy to make heat. It just needs a signal from a control device , usually a conventional Honeywell or White-Rogers thermostat. Some train stations are more efficient than others. The heating appliance (furnace) is rated with an AFUE rating, which honestly does not give the end consumer a very accurate "full story". Many experts in the heating industry agree that the "system" efficiency has more importance that the appliance efficiency. If there is significant "system loss", the most efficient heating appliance simply won't matter too much, because the heat has to get to the rooms in the house. OK, back to our train analogy.
Now, if the heat hops off before it gets to the room it is heading for, we call that "system loss". This is not good; you wasted fuel when that heat jumped off. This happens when the piping or ducting is not insulated, leaks (in duct work), and simply put, Mother Nature (OK, let's call it physics) would like to see the higher-than-ambient system temperatures equalize with the environment the heating system is in (just like our hot cup of tea will get cool, and our ice cream will eventually melt). Now, the hotter the heating distribution, the greater the potential for system loss. Also, a duct needs much more size to move the same energy compared to a hot water pipe (about 100 times more size!). So, ducts are more prone to "shed" its heat than hot water pipes. This is why PG&E currently has rebates to correct ductwork leaking.
Also- If too much heat jumps off before it reaches the end of the route, there may not be adequate heat for the last room(s). This would make for a cool room, or spotty temperatures, again, not good.
Okay- We are going to have to hunker down for this one. Are you ready? Good! This analogy applies to the conventional heating system. Let's say the train makes a delivery, and tells your thermostat, "hey stop! I'm all set! Stop the heat!" The train heads back to the station. The problem is there are still passengers on board. You spent money (fuel) to get them on board, and now they're going to have to get off the train. Why? Because your thermostat just shut down the whole system. Not only will all the heat in the heating system be wasted, but all the heat in the furnace will either right up the chimney, or it will dissipate into the furnace room. Keep in mind, it is 20 Fahrenheit outside, and you know that in another 10-20 minutes, the train will have to make another run with new passengers on board. All of these passengers have to pay for their tickets all over again. OK, if you're thinking "Joe, certainly the train did not drop off all of the heat in the pipes, there must be at least some warmth left in the pipes, and the furnace is not exactly room temperature when it goes through another cycle (train route)". My answer is "Yes, you're right". BUT what about when it is 40 degrees out? 50 degrees out? It's still heating season, right? It may be 2, 3, or 4 hours you need to schedule another train full of passengers (heat). By now, all of the heat has dissipated, all of the passengers are walking home. The passengers are not happy either, they paid for their tickets, and the thermostat, when it yelled down to the train, kicked them off.
In Europe , our proverbial train never stops, from fall to spring, 24 hours a day, the train is always moving. We call this "constant circulation". Don't get confused! The furnace isn't firing all this time. No passengers get kicked off, they all get delivered. All the passengers are very happy with the reduced rate. They paid for their tickets. How does this happen? Simple, we asked the thermostat to give up its control. We gave this control to the "variable speed fan control". With a variable speed fan control, the fan continues to circulate the air (at a low 300 rpm) even though the thermostat isn’t calling for heat. So all of the heat is still being distributed through-out the system. This also allows us to keep the air in the house from stratifying (layering) and also allow us to constantly filter the inside air. Call me for a better explaination.
These basic laws of physics are what the European heating contractors live by. You'd be lucky to find one out of ten heating contractors that can really grasp these basic concepts. It's so easy to understand, yet most contractors "already know", or don't have time or the interest to learn more. I hope you enjoyed Joe Mumford’s Heating 101!