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PART 2 of "How to save money on heating costs"

See Part 1 of this article.

(3) Insulate your home, and stop leaks

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Tip: Many utility companies will perform a free energy audit of your home and pay for part of the cost of the items below.  Take them up on it.


In an average home, 30% of the heating & cooling energy can be lost through the windows. (UMassWindows lose 10 times more heat than the same area of wall. (NRC)  So windows are important to address.

In most of the U.S. replacing single-pane windows with Energy Star windows pays for itself in less than two years. ($352-460 annual savings)  For warmer areas like California or Florida, the payback time is a few years. ($126-186 annual savings)  The EPA has a list that shows the annual savings for your particular city.

Storm windows reduce air leakage by 45-95%. (State of VT, PDF)

Besides replacing windows, here are some other ways to slow the heat through from your windows:
  • Close blinds and curtains at night.
  • Caulk the edges of windows and install weather stripping.
  • Tack clear plastic sheeting over the windows on the outside of the house with a staple gun.


When it's cold outside, run your hand along the seams of the door. If you can feel cold air coming in, you're losing a lot of heat. If you can't quite tell, use a candle instead of your hand: if the flame flickers, you're losing heat.  Install weather stripping on these doors.  It's easy, it's self-adhesive, you just stick it on the door frame and cut it. You can also screw a sweeper to the top or bottom of the door to cover the seams there.

If your door is old and poor-fitting, and you're still losing air after weather stripping, tack a heavy blanket over the door frame at night. If you can do without this door during the coldest months and use another door instead, then leave the blanket up there all the time.

Holes in the Ceiling

Older homes may have pipes or electrical conduit running from the living area through the ceiling and into the attic. Sometimes there are large gaps around the piping where it enters the ceiling. If there are gaps like this in your ceiling, caulk them. These holes suck a lot of heat from your living area into the attic, because hot air rises.


Attic insulation isn't just for summer. Hot air rises, so a poorly insulated attic means that you have heat escaping into your attic. You lose heat into your attic even if there are no holes in your ceiling -- the heat still transfers slowly through the building materials. If your attic is poorly insulated, have loose-fill insulation blown in.

Have your ducts tested for leaks. According to the Los Angeles Times (1-25-01), studies show that one out of every four homes loses as much as a third of its heating or cooling from bad ducts.

Attic stairways allow a considerable amount of heat to escape into the attic. If you have a fold-down attic stairway, add an attic stair cover.


Close the damper to the fireplace when you're not using it -- otherwise, heat will escape through the damper. Some sources say a home can lose 30% of its heat this way.

Clothes Dryer

Most clothes dryer vents are just a thin piece of metal that doesn't seal well, providing an easy way for heat to leave your home. Install a dryer vent seal to stop this.

Walls / Radiators

If you have radiators, put some cheap reflective film on the wall behind the radiator to reflect the heat back into the room rather than having it be absorbed by the wall. You can get special reflective film at a home improvement store, or just use regular aluminum foil (shiny side facing out). You can tape it directly to the wall, or wrap it around cardboard and then mount the cardboard to the wall.

(4) Turn off the heat when you're not using it

Nothing to sneeze at

You can save around 10% on your heating and cooling bills by just dialing back your thermostat back 10°–15° for eight hours. (DOE)  And contrary to popular belief, it doesn't take more energy to restore the temperature later than you save by keeping the system off.  Here's why:  The warmer your home is, the faster it loses heat, because that's the nature of heat — it flows from warmer places to colder places.  If you keep the heat on then the house is constantly losing heat quickly, and you're paying to keep re-heating the house over and over.  But when you cut the heat your home gets cool, so it stops losing heat so fast.  It takes a lot less energy to heat up the house one time when you turn the system back on, than it does to keep the house constantly topped off as it's constantly losing energy.

The only exception to this is if you have a heat pump system (very rare) and it has a "dumb" thermostat which automatically turns on the electric booster when the house is more than 5-10°F colder than the desired temperature.  In that case, the solution is to install a smart thermostat that doesn't turn on the boosters unless you explicitly ask for them.

Turn off the heat overnight

Except for the most northern climates, you should be able to remain warm enough to sleep comfortably without any heat as long as you have sufficient blankets.  If you can't stand to have the heat off completely then set it to as low as you're comfortable with — 60, 50, 40.  I've never used heat overnight and it gets into the 30's in my room sometimes when I get up in the morning.  Some people like to keep their houses warm all the time to prevent pipes from freezing, but if it's so cold that your pipes are at risk for freezing then you should be turning off the water at the meter and opening all the faucets, or using cheap heat tape, whether you're heating your home or not.

Jessica Strang writes: "I turn off the heat at night when sleeping and being in CT it is often freezing at night.  I lived overseas for 12 years in English countries and picked up a habit which I think is precious:  I order the best well-made rubber water bottles from an Indian company on the Internet which sells them all over the world.  Each are about $14, I use two of them.  You can fill them up with boiling water from an electric kettle and put them under the covers.  I figure I save money rather than heating the room and the two I use, one at my back and the other at my feet heat up the bed fantastically.  With regular use, the bottles last a good three seasons from Oct to March."

She's right about the savings. Boiling six cups of water electrically uses only 0.3 kWh of electricity, which would power a 1500-watt space heater for only twelve minutes.  You don't have to use water bottles, either, you could use clay warming bricks or electric heating pads.

Note that if you turn off the heat and it gets below 60° inside, your refrigerator could get confused and not maintain a cold temperature inside.  If this is a problem for you then you can still try turning the temperature down to 60, 55, 50, etc., finding out the lowest temperature you can go and still have a functional fridge.

To save the hassle of turning the heat off at night and on in the morning, just install a programmable thermostat which will do the job for you.

Turn off the heat while you're away

Same idea as above:  While you're away at work, don't pay to heat an empty house.  Again, install a programmable thermostat which can turn the heat off and on for you so you automatically so you don't have to mess with it.

(5) If using Central Heat, choose a system that's cheap to operate

Avoid using Central Heat if possible.

As we saw in Part 1, heating your whole house costs more than heating just part of it.  If you're not using your whole house, turn off the Central system and use space heaters in the rooms you are using.

If you must use Central Heat, the following will explain your options

Central Heat (Forced-Air) systems compared

Forced-air is a "whole house" system, which is more expensive than heating just the room(s) you're using.  It works by sucking room air into a furnace, heating it up, and then blowing it back into the rooms through registers in the ceiling or floors.  Your choices for central heat are:

Type of system

Operating Cost

Installation Cost


Geothermal Heat Pump



Payback is 5-10 years. See more about geo systems

Air Heat Pump



Not for cold climates; moderate climates only

Oil or Gas Furnace



More likely to accidentally burn down your house; can expose you to toxic byproducts of combustion

Electric Furnace

Crazy Expensive


Warm, Cold, and Coldest climates need about 27, 37, and 45 BTU's per s.f. respectively. Divide BTU's by 3400 to get kW size. So a 1000 s.f. home in a warm climate needs a 27 x 1000 ÷ 3400 = 8 kW system. If you pay 11¢/kWh, it costs 8 x $0.11 = $0.88/hr. to run it, or $214 to run it 8 hrs./day for a month. (source)

As you can see, a geothermal heat pump is the cheapest to run, and it's also the safest, though it costs a lot more to install.  Payback time is typically 5-10 years.(EPA) 

For moderate climates, an air-source heat pump is a good compromise between the cheap installation cost of gas/oil and the cheap operating cost of geothermal, since the installation and operating costs are between those of geo heat pumps and oil/gas furnaces.  Even when the air outside seems cold, there's still heat in it that can be extracted.  But the colder the outside air, the less well an air-based heat pump will work, which is why they're good for only moderate climates (rarely below freezing) and not so good in colder climates.

   See more on heat pumps, below.

Oil & gas furnaces are the most popular because they're the cheapest to install, but they have some big downsides:

  • They're expensive to operate.
  • Your house is much more likely to accidentally burn down (or explode).
  • You're possibly exposed to the toxic byproducts of combustion, which are unhealthy and potentially fatal. (EPA)

I would never use an oil or gas furnace in my own home for the last reason alone. (I use electric space heaters, in whatever room I'm in, rather than trying to heat the whole house.)

The most expensive central heating system is an electric furnace (not to be confused with the electric air-handler in a heat pump system).

Tips for forced air systems:

Change the filter. A dirty filter makes your system work harder, and run longer to get your home to a comfortable temperature. Your home improvement store sells permanent filters which you can wash with a garden hose so you don't have to replace the filter each month.

Make sure that the air can flow freely. There should be a minimum 1/4" gap on the bottom of doors so that the air can flow from a room with a closed door back to the room or hallway where the return air vent is. This is true even if you've closed the vents in the room or hallway where the return air vent is. Don't try to insulate an individual room by blocking all the ways for the air to escape back to the living area; it's SUPPOSED to flow back to the living area, even if the living area isn't heated. If the air can't flow, then the system won't be able to push much hot air through the vent into the room. Not only does this keep much hot air from actually getting into the room you want to heat, it can damage your heater since it's having a hard time pushing the air through.

Make sure the ducts don't have leaks. Many local utility companies will check your ducts for free.

Adjust dampers to even out the air flow.  If some rooms aren't getting enough heat, you can adjust the dampers, if your system has them. If so, there will be a handle on the duct to control the angle of the damper.   If this seems over your head then I suggest you have an HVAC professional adjust these for you (and show you how to do it for next time).

    You should not close registers in unused rooms to try to increase the airflow to other rooms, because you risk overheating the furnace, reducing airflow, and blowing holes in your ducts. (LBL,PDF)

Pilot lights waste energy.  Burners with a pilot light use about 7.3 therms of gas per month to keep the pilot going, or around $110/year. (my gas page)   Upgrading to a modern unit with electric ignition will save on that cost, and a modern unit will be more efficient besides.

Heat Pumps in more detail

A heat pump extracts heat from the ground or the air, which is then blown through the ducts in order to warm your home.  So a heat pump is really a forced-air system with a very efficient source for the heat.

A heat pump gets heat from the ground is a geothermal heat pump, as opposed to air-source pumps which get their heat from the air.  Geothermal pumps work a lot better but they're a lot more expensive to install.  Air-source heat pumps are cheaper to install, but they don't work in cold climates, since there's not enough heat to extract from the outside air.

Heat pumps work in reverse in the summer, cooling your home by extracting the heat from it and putting it into the ground or the air outside.  In fact, that's what a normal air conditioner does: takes the heat from the inside air and moves it to the outside air.

A geothermal system costs about $2500 per ton of capacity, so a 2.5-ton system would run $5250, and then there's the cost of drilling or excavation to install the lines underground in your yard, which runs between $10k to $20k.  ( Federal and state/local tax credits can ease that burden.)  Even with the high installation cost, savings of $2500/year are not uncommon, and the payback time is typically 5-10 years.  Savings are typically 30-70% on heating on 20-50% on cooling.(AltDotEnergy)  Bosch has a calculator to show how much you can save for your particular location.

Avoiding the "electric boost" problem with heat pumps

While heat pumps are efficient, they're not very fast.  So in some systems, when you turn them on, if there's a big difference between the room temperature and the desired temperature (say 5 to 10 degrees), the system turns on an electric booster inside the furnace to boost the heat output.  Or if it starts out with just the heat pump, if the desired temperature isn't reached in 10 minutes or so, the electric heat boosters kick in.  This electric heat costs way more than the heat pump heat, so the heat boost runs up your electric bill.

There's an easy solution:  Install a "smart" thermostat that doesn't kick in the electric boost unless you explicitly ask for it.  On proper thermostats, the boost is usually labeled "Emergency" (to indicate that you should use it only when you really need it, because it's pricey).

(6) Don't oversize your heating system

When buying a new heating system, don't get one larger than what you need.  A larger system won't heat your house any better, and it will just wind up costing you more to install.  Most HVAC contractors install a system that's too big.  Don't fall for it.

There's only one way to get an accurate estimate of the system size you need: a "Manual J" calculation to figure the heating/cooling load, and then "Manual S" to figure the size of the system based on the Manual J results.  These are systems devised by the Air Conditioning Contractors of America, and they're the only acceptable standard.  In fact, building codes require them. (PNL, ACCA)  It's best to hire an energy auditor to do the Manual J/S, because most HVAC installers don't know how to do it, and many of those who will do it, do it wrong (either out of incompetence, or because they want to sell you a bigger system than you really need). (Green Building Talk)   If you do go with an HVAC installer for a  Manual J/S, then insist on getting a printed copy of the Manual J report before they install the system.  Once you get your Manual J calculation, buy a system that matches the results; do not add a "safety" margin.  More on that below.

By the way, don't think about trying to do a Manual J calculation by yourself.  It's so complicated that even software to do it runs about $500.  The Manual J book published by ACCA is really intended as a guide for those writing such software; Manual J calcs were never intended to be done by hand.  ACCA does offer a free spreadsheet, but you'll still need the book to look up values to enter.  Here's the training video for the spreadsheet.  Good luck.

If you're looking for a quick (but not necessarily the most accurate) figure for heating needs, then the calculators from Build it Solar and Mr. HVAC will give you exactly that.  You probably don't want to use it to size the actual system for your home, though.

There's no advantage to getting a bigger system than you need.
  An oversized system will "short-cycle", repeatedly kicking in and then turning off right away because it heats up the house so fast.  Short-cycling reduces the life of the system, and can cause uneven temperatures in the house.  (The areas near the furnace warmer faster, which is usually where the thermostat is, so the system shuts off soon, before areas farther from the thermostat get warm enough.)  And again, a bigger system is more expensive (and not just for the unit itself, possibly also for the ductwork).

There's a performance penalty when an air conditioning system short-cycles, because it needs several minutes of runtime to reach optimal efficiency.  That's not true of short-cycling heating systems, because a heating system reaches maximum efficiency as soon as it turns on, since it's a very simple system.  But even without an efficiency penalty, there's still no good reason to buy an oversized system.  It'll just cost more, die sooner, and probably cause uneven temperatures in the house.  Have an energy inspector do a "Manual J" calculation to figure out how many BTUs of heating you need, and then do not get a slightly larger unit as a "safety factor". (Home Energy, IBS Advisors)

(7) Get a system with a variable-speed motor

Traditionally, the fans in central heat systems have used single-speed AC motors.  But those motors are efficient at only one speed.  So some modern systems now offer variable-speed DC motors, which are efficient over a whole range of speeds.  Variable-speed DC motors typically save 33% over AC motors on high speeds, and even more at lower speeds. (BC Hydro)  So when you're replacing your air conditioning system, consider getting one with a variable-speed DC motor.

See Part 1 of Saving Energy on Heat
or my Questions & Answers about Heating Costs

Last update: June 2013.

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