The cost of fuel is increasing and will be for the foreseeable future. This means that keeping warm or cool in your coach will be increasingly costly. Although the motorhome may seem well insulated, there are several areas where heat (or cold) can be radiated, conducted, or convected, reducing the temperature difference between outside and inside, and requiring you to use energy to compensate for the loss. Here are the main loss areas, roughly in order of importance:
The window frames are solid aluminum and conduct heat directly between outside and inside.
Most of the windows are double-paned with an air barrier in-between which is moderately effective, but the huge windshields conduct heat well with little insulation value.
Air convection currents form a loop across the face of the windows, with cooling air at the top of the window falling down the face of the window, getting colder and colder and drawing more air in from the top. The reverse situation occurs with excess heat from outside.
Although the walls and ceiling have efficient 1-1/2” thick foam insulation, they have aluminum structural elements within that lower the insulation properties. The front cab area has little insulation.
The ceiling vents are thin plastic and can lose the warmest air if the seal isn't perfect.
Air can travel directly from the outside of your furnace to the interior (you can actually see right through to the interior). You probably don't want to do anything about this because a little air exchange allows oxygen to enter and carbon dioxide to escape.
As your coach ages, the various moldings will move around, fall off, or become less pliable. If you can feel air coming into the coach from anywhere around the slide-outs, that flow will cost you.
Cold Weather Remedies
The two largest sources of heat loss are at the windows and in the front, but there are things you can do to greatly reduce the loss there by stopping or at least slowing down the convection process.
If it's cold outside and you place your hand or face under a closed window, you'll feel a steady flow of downward-flowing cool air. This convection current pulls warm air from the top of the window down across the cool surface as the air cools and gets heavier, and can exchange quite a bit of heat. Also, our window frames are solid pieces of an excellent thermal conductor (aluminum) that is exposed both outside and inside. The most effective way to reduce heat loss would be to place thick insulators over the windows and surrounding sills. The drawbacks would be that you couldn't see out the windows, and handling and storing these insulators would be a hassle.
However, greatly slowing the convection process can be achieved by closing up the gap at the bottom of the window so the cold air gets trapped between the window and the shades. What I've used with good success are foam water pipe insulation tubes, available from any hardware store in sizes fitting ½", ¾", 1", and other pipe diameters in four foot lengths, that I wedge between the lift bar of the shade and the window frame. Different sizes must be used unless you make all spacings between the window and shade uniform, because it's obvious that Fleetwood doesn't use templates to determine where to drill holes for the cord tensioners. I moved some of these tensioners but still ended up with a few different sizes to get the best fit. Get the best grade of foam (usually black), because they're only about $4 each, and label each piece showing where they were fitted to (L2, L3, R3, etc.). You can probably recoup the cost of these tubes in a month or so. Admittedly it's a little hassle to wedge them back into place if you raise and lower the day shades, but the trade-off seems well worth it if temperatures dip below about 40 degrees. In addition to stopping the convection dramatically, it also insulates at least the bottom piece of aluminum sill on the inside, reducing direct conduction.
As for the front cab area, the solid windshields are unfortunately a good conductor of heat and cold. You are probably using the existing inside windshield shade already, but it's easy for the air to get around it. There's also little insulation in the bulkhead between the generator compartment and the coach interior. My fix for this is installing drapes directly behind the front seats that can either be tied back to the sides (using the existing tie-backs) or be stretched fully across the width of the coach. DrapesMounting They extend from the very top of the ceiling to touching the floor. This greatly slows the convection currents in the front area from cooling the rest of the coach interior. With the drapes fully across overnight in sub-40 degree weather you can definitely feel the difference in temperatures between the front and the rest of the coach in the morning, meaning there has been a savings by not having to heat the front. Although I'm 6'2" tall, there is no problem with vertical clearance on the support bar, and the rubber cups and brackets I used allow it to be removed if not being used (and the brackets could be used to hang coats on). As for the drape material, check out Wal-Mart's end-of-roll bargains ($1/yd), because they can have great drape material normally costing a lot more. For 5 yards of material and eight straight seams on a sewing machine you can experiment at a total cost of about $20 with the mounting hardware.
You could close the bedroom door and only heat Zone 2, but this would be a last resort, because you'll be using the rest of the interior for everyday living sooner or later (except for the driver area).
I haven't done anything with the ceiling vents nor the air coming through the furnace compartment because the thermal loss isn't that great, and a small amount of fresh air can be a good thing. And the moldings around the slide-outs are still working well on the 2004 Discovery.
As for sources of heat, we've all got the dual furnaces totaling about 45k BTU. What I don't like about using these heaters is that it's generally a hassle to get the propane tank refilled, and gauging the amount of propane remaining is tricky. The temperature of the propane tank can change the reading by almost a quarter tank, and the pressure of the gas that the sensor measures doesn't fall much until most of the liquid is gone. You definitely don't want to run out of propane in case things get really cold. The worst part though is that when the furnaces kick on, there's a lot of commotion that can ruin sleep for you and your neighbors.
Many campgrounds have rules against using electricity to heat the coach, especially those in areas like southern California and the northeast where the cost per kilowatt of electricity can be three times what it is in other parts of the county (16 cents vs. 5 cents). But when we can, we use 1500-watt space heaters, because they are almost silent and are pretty safe even if inadvertently you let flammable materials obstruct the face. Each heater puts out about 5000 BTU's, and we've found that usually one heater will keep things toasty, given the above insulating measures. In our coach when the night temperatures got down to the upper teens, three heaters did the job, and the Discovery will support three of these heaters if you've got 50-amp service and you know where to plug them in. Plugging one into the outlet under the galley table and one into the outlet on the end of the kitchen L-extension (one set to high at 12 amps and one set to low at 4 amps), you'll be safely under the Inverter "Out1" 20 breaker allowance. And with one heater set to high on the outlet in the bedroom fed by the General Purpose 20 amp breaker, you'll get a total of about 11000 BTU's which will keep the interior in the mid- 60's down to an outside temperature of about 20 degrees (with pipe foam and drapes).
The heat pump in the forward A/C unit will work down to about 40 degrees, but any lower than that and you will not get any usable warmth out of it even though it cycles on and off continuously. It makes about the same noise as a furnace when it kicks on.
At temperatures substantially below freezing, regardless of how you heat the interior, you may find that the holding tank dump valves freeze, because they stick out in the uninsulated water compartment and don't hold enough water in them to absorb the cold. Using a water pipe heater cord wrapped around the valves works well there, and these cords only turn on when the temperature inside the compartment gets to or below freezing. The heat is distributed gently so there's less of a fire risk inside the compartment than when using lightbulbs or space heaters. Finally, adding a foam collar around the sewage discharge hose will help hold heat better in that compartment. Picture
Another freeze protection technique is to let the water run slowly at the furthest outlet from the source so there's a constant flow of water, but we've not had to resort to this approach.
Hot Weather Remedies
Methods for insulating against heat are different from trying to keep the cold out. The pipe insulation wedged under the blinds will be less effective because there is less upward draft against the windows, but keeping the blinds closed will reduce the convection around the windows. Drapes between the front section of the coach and the rest of the coach will work well to block the airflow caused by the solar heat through the windshield and conduction through the front bulkheads (if you don't mind not being able to watch the front TV set).
Many people already use an exterior windshield cover made of woven nylon or PVC for privacy, and that stops about 70 percent of the solar radiation from getting inside the coach through the windshield in the first place. We have covers for all of the other windows also that keep a fair amount of heat out, in addition to providing additional privacy.
Window tinting film is available in either permanent or flexible plastic removable form. But because we have dual pane windows, the manufacturers do not recommend using these products on our windows because the heat would be trapped in-between the panes and could lead to expensive failure of the window. We've tried a sample of the removable type applied on the outside of the window, and it's held up through miles of 70 mph travel, but it's almost impossible to get a bubble-free application so the results, at least for us, are aesthetically unacceptable. You might have better luck applying the film. Ideally, a mirrored tint applied on the inside of the outer pane of glass (as in some upper-end coaches) would provide cooling, privacy, adequate visibility, yet wouldn't jeopardize the integrity of the dual pane window.
If the temperature gets too hot, you will not be able to get the coach interior to a comfortable temperature because air conditioners can only reduce air temperature by a certain number of degrees (about 20 degrees between the air entering the unit and exiting the unit for the Coleman Mach series), but mainly because the total number of BTU's of cooling provided by the two units cannot match the BTU's of heat entering the interior. But using the above approaches will allow you to get to cooler temperatures by reducing the amount of heat being able to get into the coach.