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Home heating and cooling, explained plainly.

Straight answers from an HVAC engineer: why your system does what it does, and what actually lowers the bill.

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Why Do the Lights Dim When the Heat Kicks On?

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A compressor pulls about six times its running current for under a second, and the lights show it. Your heat pump starts, and for a split second every light in the kitchen sags. Then it is over. In most houses that blink is normal. The compressor in the outdoor unit takes a big gulp of electricity to get spinning, about six times what it draws once it is running, and your wiring cannot hand over that much without the voltage sagging for a moment. The thing to watch is not whether it happens, but whether it is getting deeper or lasting longer. A big gulp, then a sip Every motor is hardest to start from a dead stop. Think of pushing a stalled car. The first shove takes everything you have, and keeping it rolling takes a light push. A compressor is the same. Standing still, its motor lets current pour in almost unchecked. As it spins up, that current falls fast, and in well under a second it settles at its normal draw. Here is where the lights come in. Electricity reaches your ...
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Water Heater Warm to the Touch? That Heat Is on Your Bill

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The touch test: a bare older tank feels warm because heat is leaving it all day; a wrapped one loses far less. Put your hand flat on the side of your water heater. If the steel feels warm, you are paying to heat the basement, one quiet degree at a time. On an older electric tank that warmth can add up to about $40 a year in heat you never use, and a $20 to $30 insulating blanket gets most of it back in a Saturday morning. Newer tanks and gas tanks are a different story, and I will get to them. Why a warm tank is an expensive tank A storage water heater keeps 50 gallons (189 L) of water at about 120 degrees F (49 degrees C) around the clock, whether anyone showers or not. The basement around it might sit at 60 degrees F (16 degrees C). Heat flows from warm to cold, so the tank leaks heat through its walls all night and the element or burner keeps switching on to replace it. Engineers call this standby loss. Think of a mug of coffee. A thin mug gets hot on the outside and the coffe...
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Why the First Heat of the Season Smells Like Burning

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Three smells when the heat comes on, and what each one means You turn the heat on for the first time this fall, and within a minute the whole house smells like something is burning. Almost always, something is: the dust that settled on the hot parts of your heating system over the summer. It should fade within the first hour. Only two smells mean stop right now, and telling them apart takes about ten seconds. Six months of dust meets a hot surface From spring to fall, the heating side of your system just sits. Dust drifts in and settles on the heat exchanger, the metal box the burner heats and the blower pushes air across. In a heat pump it settles on the electric backup coils. In a radiator home, which is most of Europe, it collects between the fins and behind the panel. Then the first cold night arrives. Those surfaces go from room temperature to several hundred degrees in minutes. Household dust is mostly skin flakes, lint and pet hair, and all of it scorches at that heat. Th...
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A $3 Sheet of Plastic Can Halve a Window's Heat Loss

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Bare glass versus the same window with a taped film: about half the heat loss. Hold your hand near a bare window on a cold night and you can feel the heat leaving the room. The fix is cheaper than almost anything else in home energy: a clear plastic film kit, taped to the window frame and shrunk tight with a hair dryer. On a single-pane window it cuts the heat flowing out through the glass by about half. On a double-pane window, by about a third. Glass is not the insulator. The air is. This is the part that surprises people. A pane of glass barely slows heat at all. Almost all of a bare window's insulating value comes from the thin layer of still air that clings to each side of the glass. Those two air layers do the work. The glass just holds them apart. A film kit adds a second pocket of trapped air, about an inch (2.5 cm) deep, between the film and the glass. That pocket resists heat about as well as the two air layers combined. So the window ends up with roughly double the...
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Did You Overpay for Your AC? A Lawsuit Says Maybe

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Price change since January 2020 as stated in the class-action complaint: HVAC equipment, kitchen appliances, and prices in general. Seven companies that make most of the air conditioners, furnaces and heat pumps sold in the United States are being sued for fixing prices. On October 9 they asked a federal judge in Michigan to throw the case out. Here is the short version. Nothing in the case changes what you should do this fall, and the biggest savings on a new system still come from the quotes you collect, not from a courtroom. What the lawsuit says, and what the makers say back The suits were filed this spring by homeowners and by contractors. They name Carrier, Trane, Lennox, Daikin, Rheem, Bosch and AAON, which between them sell most of the heating and cooling equipment in the country. The claim is simple: since 2020 these companies raised prices in step with each other, by more than their costs went up, and signaled their plans to one another through public announcements an...
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A Warm Winter Is Forecast. Will Your Heating Bill Drop?

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A winter that runs 1 °F warmer uses about 6% less heating fuel. One hard cold week can give most of that back. NOAA's winter outlook came out last week, and for most of the northern half of the country the headline is a warmer-than-average winter, pushed by one of the strongest El Niños on record. So yes, if that holds, you will burn less fuel. But less is not zero, and the forecast is a tilt of the odds, not a promise. The useful question is what a warm winter is actually worth to your house, and what to do about the cold weeks that still come. Your furnace counts degree days, not forecasts Your heating system does not care about the season's average. It cares about every single day, and how far below about 65 °F (18 °C) that day sits. Utilities call that gap a degree day: the colder the day, the more degree days it adds, and the more heat your house asks for. Think of a bucket with a hole in it. The colder it is outside, the bigger the hole, and your furnace or heat pump i...
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Furnace Turning On and Off Every 5 Minutes?

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Two timelines: a healthy furnace runs in one long stretch of 10 to 15 minutes; a short-cycling furnace runs in three-minute bursts with gaps between  A healthy furnace runs long and rests long. Short cycling is many short burns an hour. The furnace lights, runs a few minutes, shuts off, and a little later does it again. All evening. That stop-and-start pattern is called short cycling, and most of the time it begins with air, not with the burner. Pull the filter first. If a fresh one does not fix it, the furnace is probably too big for the house, or the thermostat is sitting in the wrong spot. What a healthy cycle looks like A furnace is built to run in long, steady stretches. On a cold evening it comes on, runs 10 to 15 minutes or more, and stops when the thermostat is satisfied. Short cycling means it keeps quitting after a few minutes, over and over, often before the house is warm. Inside, a safety switch watches how hot the metal gets where the air picks up heat. It counts ...
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