Choose the Right Tools

To do this sort of work, you’ll need a few basic tools. None are very expensive, and can be had for just a few bucks at stores like Harbor Freight, Home Depot, or Walmart:

• Non-contact voltage detector: These are indispensable for electrical work around the house. They’re like an electric pen that can sense electrical voltage—press the button, hold it to the small plug slot on an electrical outlet, or to the screw terminals of a switch, and it starts flashing and beeping if the circuit is powered (Figure 47). They’re much easier to use and safer than a multimeter when you just need to make sure that a wire isn’t hot. If you need help choosing one, check out Wirecutter’s guide.

  

• Plug-in outlet tester: I don’t go into outlet replacements in this book, but in case you ever do replace one, or just want to test one you have, these cheap gizmos are essential. Simply plug it into an outlet and see which lights turn on (Figure 48). Check it against the guide printed on the tester itself to make sure the outlet is working correctly. They’re easy to use and help prevent equipment damage and fire. Fire bad. I use one similar to this, but there are several kinds on the market.

  

• Multimeter: Multimeters aren’t the easiest gadgets to use, but they’re an essential part of any electrical toolkit. They can measure resistance, capacitance, and voltage in AC or DC. You probably don’t need one for anything I discuss in this book, but they’re useful for checking for bad grounds, broken connections, low voltage, and various wiring problems. More-expensive models can measure all kinds of other stuff. You can spend hundreds on one, but you can find one with enough features for our purposes for under $10. I use this cheap one from Harbor Freight, which is best described as “sufficient,” and Harbor Freight often gives them away for free.

• Needle-nose pliers: Home electrical work involves manipulating and twisting thick electrical wire, and there is no better tool for it than needle-nose pliers. Again, they don’t have to be expensive. Wirecutter has some recommendations here as well.

• Wire strippers/cutters: Surprisingly, I don’t find that I need these much, because most of the wires I use come pre-stripped. I usually just use a simple pocket knife if I need to trim any insulation. Some needle-nose pliers have built-in cutters and/or strippers. Unsurprisingly, Wirecutter has recommendations for, uh, wire cutters.

• Screwdrivers: You’ll need basic flat-head and Philips screwdrivers in a variety of sizes. Use the right size for the job so you don’t strip the screw head! Most electrical components, including light switches and wall outlets, as well as outlet and switch covers, use fairly standard screw sizes, so you’ll likely need only one flat-head and one Phillips.

Break the Connection

Before fooling around with electrical wires, you need to cut power to that circuit! In most modern homes that’s accomplished via a breaker box, which acts as a central panel for your home’s electrical circuitry. Each circuit is wired to a circuit breaker, which you can flip to turn on or off (Figure 49).

The trick is figuring out which breaker goes to the circuit you need to turn off. If your breaker box is well labeled, that’s easy. Otherwise, you’re going to have to use trial and error to figure it out. Here’s the method I’ve adopted, and it’s been serving me well for years:

1. Verify that the outlet or switch is receiving power and verify that your tester is working correctly. I test it with either a voltage detector or multimeter. If it’s a light switch, I turn it on. If it’s an outlet, I plug in a lamp or other simple electrical appliance and turn it on.

2. If you have a partner (highly recommended), have them stand by the test light—if they’re not in earshot, preferably with a phone or walkie-talkie so you can talk to each other.

3. If you have any electronics that don’t react well to having their power cut abruptly (for example, a computer without a UPS, a NAS, or some DVRs), be sure to shut them down gracefully before turning off any circuits.

4. Go to your breaker box and make an educated guess about which breaker it might be. If you have no labels to go on, work systematically by starting at one end and moving in a single direction. Flip a breaker off, see (or have your partner tell you) if your light is still on, and then flip it back on again. If the light turned out, you’ve found the breaker; if not, move on to the next one. (If the light isn’t in view and you don’t have a partner, you’re going to have to do a lot of walking.)

5. Once you have identified the correct breaker, make sure it’s off, then test the outlet or switch with your tester to ensure that the power is off. Bonus points if you label the breaker for future reference.

If worse comes to worse and you can’t figure out which breaker to kill, you can turn off the main power, which should be an extra-large breaker at the top of the box. That cuts power to your entire house, so make sure to have portable lighting on hand!

Check for the C-Wire

Behind every thermostat is a series of wires, each represented by a letter. The C-wire is also known as the “common wire,” but in reality it’s not as common as would be ideal. In essence, the C-wire, found most commonly in newer HVAC systems, delivers more power to power-hungry thermostats like the ecobee.

You don’t need the C-wire to power an ecobee thermostat—the ecobee4 comes with a device called the Power Extender Kit (PEK), which is attached at the actual HVAC unit rather than the thermostat. ecobee offers installation instructions for the PEK, but I would recommend consulting a professional for two reasons: it involves working around high voltage, which can be dangerous to yourself and your HVAC system, and the PEK works by “stealing” power from other wires in your system, which could strain your system and shorten its lifespan. Take your chances if you like, but if I didn’t have a C-wire, I’d call a pro. I’ve heard from a few people who said they had a C-wire added inexpensively, which would be a better solution if it’s cost-effective.

Fortunately, figuring out if you have a C-wire is easy: just crack open your thermostat. Usually, this is as easy as pulling the cover off. But before you start yanking, look to see if there are any tabs you need to press or screws to remove.

Once you get the cover off, you should see a series of small wires connected to terminals as shown in Figure 54.

If you see a C-wire, you should be able to install the ecobee thermostat without any trouble. If you don’t see it, consult an HVAC specialist and discuss your options. They may be able to install a C-wire inexpensively, which would be a better solution than the PEK.

If you’re not installing the ecobee right away, go ahead and put your thermostat cover back on for now.

Prepare to Install the ecobee

Once you have your ecobee in hand, it’s time to review the included parts (Figure 55). Be sure to also read through the included instruction manual!

Here are the main parts of the ecobee4 (other models should be similar):

1. Power Extender Kit: If you don’t have a C-wire, you’d attach this to the actual HVAC unit to power the thermostat. I won’t be covering that procedure in this book.

2. ecobee thermostat: This is the actual unit that you’ll be interacting with on a daily basis. Be extra careful with this part!

3. Trim plate: Usually when you remove an old thermostat, it reveals holes and unpainted spots. If your old thermostat was larger than the ecobee, the ecobee may not fully cover these blemishes. This included plate goes between the ecobee and the wall to make things look nice. If the ecobee completely covers these flaws, you can ignore this piece—the ecobee looks better on the wall without it.

4. ecobee backplate: This is the part that is attached to the wall, to which you connect your HVAC system’s wires. The ecobee thermostat plugs into this part. If you use the trim plate, the backplate snaps into it.

5. Screws and drywall anchors: These are used to secure the backplate and trim plate to the wall.

6. Wire labels: These included labels are useful for labeling each of your thermostat wires as you disconnect them from the old thermostat—it’s a lot easier to connect them to the new thermostat if they’re labeled.

7. Remote sensor and stand: Higher-end ecobee models, such as the ecobee4, include one of these remote sensors, which can sense temperature and occupancy in other rooms in your house. The ecobee3 lite does not include remote sensors, but you can purchase them separately. See Set Up ecobee Sensors.

Before getting started, you’ll also want to have these tools:

• Small flat-head screwdriver: You’ll need this to loosen the thermostat wires.

• Drill and bits: You’ll need to make a couple of holes in your wall, and these are the best tools to do so.

• Phillips-head screwdriver: Just a regular old screwdriver.

• Needle-nose pliers: For manipulating small wires.

• Hammer or mallet: Just in case you have a stubborn drywall anchor.

Now you have the parts and you have the tools. There’s one last thing to do before getting started: figure out how to wire the thermostat.

Get a scrap piece of paper. Make two columns: one for your existing thermostat and another for your ecobee (Figure 56). Take the cover off your existing thermostat, and in its column on the paper, write down the letter the wire is connected to and the color of the wire. Besides helping you plan out your wiring, it also acts as a reference in case you lose a wire label.

Next, look at your ecobee backplate and see which wires line up with your existing thermostat. On my thermostat, G, O, and C directly lined up with terminals on the ecobee backplate (my O wire lined up with the ecobee O/B terminal).

I had to consult the manual for the Y and R wires; the manual told me to connect the Y wire to the Y1 terminal and R to the Rc terminal.

But I was left with one mystery to solve: the white wire, which was connected to the Aux terminal on my existing thermostat, which was in turn jumpered to the E terminal (refer back to Figure 54). Fortunately, ecobee supplies several wiring diagrams on the company’s website, and I found this one that suggested connecting Aux and E to the W1 terminal on the ecobee. Additional research confirmed this to be correct.

Write all of this down so you can refer to it as you’re wiring your ecobee. Save it for later reference!

Remove Your Old Thermostat

Once you know how you’re going to wire your new thermostat, it’s time to uninstall the old one. This is a straightforward process, but some care must be taken.

First, turn the HVAC system off at the thermostat. The reason to do this is because when you’re setting up the ecobee, one of the first questions it asks you is what the old thermostat was set to, so the ecobee can sync to your system. Just turn it off to avoid any hassle.

Next, you need to turn off the breaker for both the inside and outside portions of your HVAC system. The risk of electrical shock from a thermostat is low, but the bigger risk is creating a short as you’re manipulating the wires, which could cause expensive damage to your HVAC equipment. It’s best practice to kill the power while you’re replacing the thermostat.

I explained how to cut breakers in Break the Connection. ecobee recommends testing the breakers by turning your thermostat on and seeing if any air blows out of the vent after the breaker is off. I was fortunate enough to have well-labeled breakers and a thermostat powered by a C-wire, so this part was easy—when I turned the breaker off, the thermostat also turned off.

Once the power is off, loosen each wire from the existing thermostat terminal by turning its screw counterclockwise, labeling the wire with one of the included labels, if you have a label for that wire (Figure 57).

Don’t bother removing any jumper wires unless ecobee recommends jumping two terminals on the ecobee unit. The manual instructed me to not jump any R wires that may have been jumped on the old thermostat, and I saw no reason to fool with the jumper wire connecting Aux and E on my old thermostat, because both of those corresponded with the W1 terminal on the ecobee. In many cases, the ecobee is smart enough to handle any required jumping via software.

Once all the wires are removed from the existing thermostat, it’s time to unmount the thermostat unit from the wall. As you can see in Figure 57, I just had to remove two screws.

Install the ecobee Backplate

At this point, you have a hole in your wall with colored wires sticking out, and you’re probably looking at some drywall anchors that held the old thermostat in place. Time to finish the job:

1. Decide whether you want to use the trim plate. Just hold the ecobee thermostat up to the wall to see if it would completely cover the unpainted spots (Figure 58). If it won’t, and you won’t be patching and painting the wall right now, you should use the plate.

   

2. I’m going to assume that you’ll use the trim plate. Fortunately, pairing the backplate to the trim plate is easy: just line up the square holes and snap them together.

3. You need to mount the backplate to the wall, with or without the trim plate attached. To do so, first you need to line up the backplate with the wall. Chances are that your wires are all over the place after detaching them from the old thermostat and labeling them. Carefully arrange your wires into a neat bundle that will fit through the hole in the backplate and/or trim plate.

4. Thread the wires through the backplate hole so that the plates sit flush against the wall. The first time I tried this, I didn’t thread the unused wires through, so it wobbled a bit. If you have unused wires, thread them through, as well.

5. Once the wires are through, and the backplate is flush against the wall, level out the plates and mark where to drill the mounting holes.

   Usually when you install a thermostat, you have to balance a level on top of the unit when you’re lining it up. But many modern thermostats, including the ecobee, include a small level on the backplate! Just rotate the plate until the bubble is perfectly centered between the two lines.

   To mark the location of the holes you’ll need to drill for the mounting screws, I recommend taking one of those screws, putting it through one of the two holes, and gently pressing the tip against the drywall; repeat for the other hole. Then take a sharp pencil, find the indentation, and mark it with the pencil lead. Remove the plate(s) from the wall.

Before you grab your drill, let’s talk mounting solutions. If you have wood paneling or some other sort of solid wall surface, or if there happens to be a wall stud behind one of your mounting marks, you won’t need to use the included drywall anchors for those screws—just drill a pilot hole and then screw them into the wall.

But most modern homes have chalky drywall, which is cheap, easy to paint, attractive, and easily repaired, but can’t hold much weight. So they invented these little plastic doodads called drywall anchors. You drill a hole in the drywall just big enough for the anchor’s tip to go into, and then place the tip of a screwdriver into the hole on the anchor and screw it into the wall. You then insert the screw into the opening on the drywall anchor—the anchor helps support the weight of whatever you’re screwing to the wall. Refer back to Figure 58—the drywall anchors are those blue things in the wall.

You always need drywall anchors when screwing stuff to drywall unless there’s a stud—a 2x4 piece of lumber that serves as part of your wall’s skeleton—behind one of your mounting holes. When drilling, you’ll know you’ve hit a stud if you have an especially hard time drilling and/or you see wood chips on the drill bit’s flutes. Its unlikely you’ll hit a stud here, but contractors make odd decisions sometimes when framing houses.

With an understanding of wall fixtures under your belt, pick up your drill and choose a bit. ecobee recommends a 3/16" bit if you’re using the included wall anchors. Always start with the smallest bit and work your way up, because it’s much easier to widen a hole than it is to undrill it! I started with a 3/32" bit and worked my way up.

In theory, if you’re working with drywall, this is how this should work:

1. Drill a 3/32" hole in each of the spots you marked with a pencil.

2. Insert the tip of the included drywall anchors into holes.

3. Insert a Phillips screwdriver into the hole of the drywall anchor and turn the screwdriver clockwise while putting gentle pressure on it.

4. Once the flared edges of the drywall anchor are flush to the drywall, put the ecobee plates back into position, carefully threading the thermostat wires through the center hole, insert each included screw through the holes in the backplate into the hole in its corresponding drywall anchor, and use a screwdriver to tighten the screws to affix the thermostat to the wall.

Once the plate(s) are affixed to the wall, tug them gently to make sure the backplate is not going to fall off and break your fancy thermostat (and probably take a chunk of drywall with it). Don’t try to do pull-ups here—just make sure that the plate(s) are secure to the wall.

Now it’s time to put the wires into the terminals. Take one wire at a time and insert its bare tip into the side of the proper terminal (Figure 59). Each terminal has two holes: one in the front and one in the side. Do not stick the wire in the front hole, as those are where the pins on the back of the actual thermostat go.

To insert the wire, just stick the bare end into the side hole and push it in until you feel a click. Needle-nose pliers are useful here for pushing the wire in firmly. As you insert the wire into the terminal, the little lever at the opposite side of that terminal should depress itself and then pop back into position. Some of mine stayed depressed, probably because the wire tips were so long. Regardless, they seem to be well in place.

If a wire seems too short to get far enough into a terminal to click, try gently pulling it until you can get the end locked into the terminal. I had to do that for my G wire. (If you put the wrong wire in a terminal and need to remove it, just press the little lever to release the wire.)

When finished, gently tug each wire to make sure it’s not going to pop out on its own.

If you did everything right, the hard part is over!

Finish the ecobee Installation

Take the thermostat (the black, shiny part) and push it onto the wall plate. Look at the back of the thermostat. See those little pins? They go into those front-facing holes on the backplate, the ones that you weren’t supposed to stick wires in! It should be as simple as pushing the thermostat in place until it clicks. Very gently wiggle the thermostat to make sure it’s secure.

Now is the moment of truth. Turn the breaker back on, and your ecobee should turn on and say “hi,” followed by “please give me a moment while I stretch my wings” (Figure 60).

If the thermostat doesn’t turn on, double-check your wiring, contact ecobee support, and/or call an HVAC professional.

Now the ecobee guides you through HVAC configuration. It first asks questions about the thermostat wiring, which you should know the answers to.

It then asks if you have an accessory connected to your thermostat, like a humidifier, dehumidifier, or ventilator. You likely do if you have an ACC wire. Follow the onscreen instructions to set that up or seek additional help.

Next you’ll be asked if you want temperature in Fahrenheit or Celsius. Choose wisely.

If the ecobee asks what type of heat pump you have, you can choose air to air or geothermal. It offers some guidance here, but I’d assume you’d know if you had a geothermal unit, since they’re somewhat rare.

Next is a very tricky question: is your O/B reversing valve energized on cool or on heat? The good news is that getting this wrong won’t damage your system, but if you choose incorrectly, you’ll get cold air when you want heat. Follow the ecobee’s advice and set it to “Energize on cool” at first, since that’s the most common configuration. If that turns out to be wrong later, you can go back to the settings screen on the thermostat and go to Settings > Installation Settings > Equipment > Heat Pump > O/B Reversing Valve to change it.

Next up is another tricky question: let the heat pump and aux heat run simultaneously? The ecobee warns to set it to Disable if your auxiliary heat is natural gas or oil. My auxiliary heat is an electric heat pack, so I enabled it to allow smoother transition between my electric heat pump and my electric heat pack.

Next you’re asked the minimum outdoor temperature for your compressor, assuming you have one. The default is 35°F, which is a safe default for an air-to-air pump. Any colder and the ecobee turns off the heat pump and switches to auxiliary heat to avoid damaging the pump.

The next question is likely whether you have a furnace or a boiler. Choose appropriately for your home.

Next, you may be asked whether you want your fan to be controlled by the ecobee or the furnace. ecobee recommends that it should control the fan, but I found that caused cold air to blow out of my vents when I turned the heat on, and it’s apparently a common problem. I recommend setting this to By Furnace; you can always switch it back later.

You’re asked to name your ecobee. Choose what you like—I just went with the default My ecobee because it’s descriptive, and it hasn’t given me any problems. If you have a multi-zone HVAC system, you probably want to give the ecobee a name that describes where it is in your home, like Bedrooms.

Next you’re asked to set up Wi-Fi access for the thermostat. The easiest option is Use iPhone, iPad, or iPod. You’ll be prompted to go to Settings > Wi-Fi on your iOS device and choose the ecobee under Set Up New Device, followed by choosing the Wi-Fi network (Figure 62).

After Wi-Fi is established, you’ll be asked what the current mode of your HVAC system is. If you followed my advice, it should be Off. Otherwise, see if you can tell from looking at your old, disconnected thermostat.

You’re asked ideal home temperatures during summer and winter. Enter what you like here.

You’re prompted to enable Smart Home/Away. Some ecobee models can detect home occupancy (via motion detectors in the thermostat and remote sensors), and they use that information to automatically set Home and Away settings to reduce energy usage when no one is home. I find that this works pretty well, but Disable it if you’re unsure.

You’re asked to choose your country of residence and time zone, and then you’re presented with a registration code that you’ll use to connect your thermostat to the ecobee service, which is required to connect it to HomeKit. Be sure to save this code!

At this point, your thermostat is set up, but it will not be operational until the calibration process is complete. This only took a few minutes for me, but some users report it taking several hours.

Connect ecobee to HomeKit

Don’t bother digging through the ecobee packaging for a HomeKit code. The only way to link the ecobee thermostat to HomeKit is to do so via the ecobee app, which involves linking your thermostat to ecobee’s online service.

When you first open the ecobee app, you need to enter the registration code you were given when you set up the thermostat. If you didn’t save that, don’t fret—tap the menu button on the thermostat followed by Registration and Continue to view it again. Tap Finish on the thermostat when you’re done.

After you use the app to set up an ecobee account, you’ll be asked whether you want to enable the weather service, which lets you check the current weather and forecast on your thermostat. I like to turn this on because it’s a handy feature. At the next screen, when you’re asked for your address, you don’t have to enter your full address—just the city and state to get a weather report.

You’re asked whether to enable Home IQ, which lets you track system usage and energy consumption on the ecobee web portal. I left it on, but if you’re particularly privacy conscious, you may want to turn it off. If you turn it on, you’ll have to provide details about your home such as the square footage. If you don’t have that handy or don’t want to provide that, leave Home IQ off.

If you’re using an ecobee4, which has Amazon’s Alexa voice assistant built in, you’re prompted to set it up by linking to an Amazon account.

Once the app is set up, you can finally set up HomeKit. Refer to ecobee’s website for the most up-to-date instructions.

Use the ecobee

If you’ve read Use Accessories, you shouldn’t have much trouble controlling the ecobee thermostat, but I’ll offer some quick tips here:

• Sync between the ecobee app and HomeKit is nearly perfect, so feel free to control your thermostat with whichever is more convenient at the time.

• The ecobee is designed to let you set up schedules, using the app, based on when you’re home, away, or asleep, which are called Comfort Settings. To configure these, choose your ecobee in the app, tap the menu button at the bottom of the screen, and choose Schedule. Tap the plus button to add a new schedule item. Choose a comfort setting (by default: Home, Away, and Sleep) and a start time, and tap done.

• To manually control your thermostat with the Home app, tap the ecobee’s accessory tile. Use the wheel to switch between Off, Heat, Cool, and Auto. (Auto lets you specify thresholds that turn on the heat or the air conditioning.) The slider lets you set the desired temperature.

• While you can create regular scenes in the Home app, creating them in the ecobee app lets you call upon your Comfort Settings. To do so, go to the Account screen, tap HomeKit, tap Scenes, and then tap the plus button in the upper-right corner.

Set Up ecobee Sensors

The ecobee4 includes a separate room sensor, which you can also purchase separately or in bundles of two if you want additional sensors, or if you have an ecobee3 lite. Each of these small, battery-powered sensors detects occupancy (via movement) and temperature. You can set them up to help the ecobee balance out the temperatures in occupied rooms, and to allow the ecobee to automatically switch between Comfort Settings based on whether or not someone is home.

Setting up room sensors is easy. Just flip one over, pull out the plastic tab to turn it on, and pop off the battery cover. Notice how the battery cover has a hole in it. That’s so you can use the included screw and anchor to install the sensor on your wall. If you don’t want to do that, replace the battery cover with the included stand, which just pops into place. Wherever you place the sensor, keep it out of direct sunlight, but in a frequently trafficked area so it can pick up movement—near a doorway is good.

To finish setup, return back to the thermostat and follow the onscreen prompts to set up the sensor and pick which room it resides in.

Troubleshoot the ecobee Thermostat

If your ecobee gives you much trouble, I highly recommend using ecobee support or contacting a qualified HVAC technician. But there are often issues you can quickly fix yourself.

Here’s how to fix common ecobee problems:

• Various issues—check the wiring: It’s possible that a wire isn’t fully inserted in its terminal without being obvious from a visual inspection. Thankfully, the ecobee itself can tell you which wires are connected: from the thermostat main menu, check in Settings > Installation Settings > Equipment > Wiring.

• Cold air when you want heat: First, understand that it may take your heat pump a few minutes to get up to temperature, especially if it’s very cold outside. To make sure that your vents aren’t blowing cold air, I find that an infrared thermometer like my Etekcity Lasergrip is handy. If the temperature at the vent is higher than it is around the vent, I know for sure I’m getting warm air, and I can track it getting warmer over time.

  If you’re not getting warm air, or if it never seems to get warm enough, here are a few things I would check:

  • When you set up the thermostat, if you were asked if the O/B reversing valve energized on cool or on heat, go to Installation Settings > Equipment > Heat Pump > O/B Reversing Valve and change it to the opposite of what it’s set to. If cold air is still coming out of the vent when you want heat, switch it back, because that wasn’t the problem.

  • During setup, if you set it so that the thermostat controls your fan, I’ve found that often the ecobee kicks the fan on well before the pump is putting out warm air. Try setting it so that your HVAC system controls the fan instead in Installation Settings > Equipment > Furnace > Fan Control in Heat Mode.

  • By default, the ecobee keeps the fan on for a few seconds after the heat has stopped in order to circulate the remnants of the heat in your ducts. I personally don’t like this; you can turn it off in Installation Settings > Thresholds > Heat Dissipation Time.

  • If it’s very cold outside, it’s possible that your heat pump can’t work efficiently enough to keep you warm. Consider locking it out below a certain temperature in Installation Settings > Thresholds > Compressor Min Outdoor Temperature.

• Aux running too long: If you have auxiliary heat and get a message complaining that it has been running too long, there may not be any reason to be concerned. If it’s super cold, your auxiliary heat runs more! You can adjust the threshold for the warning in Reminders & Alerts > Preferences > Aux Heat Runtime Alert. But if you’re worried that it actually is running too long, here are some things to try:

  • Check your heat pump lockout temperature in Installation Settings > Thresholds > Compressor Min Outdoor Temperature—it may be too low. Refer back to This COP Can Save You Money to learn how low you can set your lockout.

  • If your aux is running too long when it’s relatively warm outside, lower your Aux lockout in Settings > Installation Settings > Thresholds > Aux Heat Max Outdoor Temperature.

  • It’s also worth checking Settings > Installation Settings > Thresholds > Compressor to Aux Temperature Delta, which controls “the minimum number of degrees from the desired temperature before engaging the auxiliary heat.”

  • Also look at the Settings > Installation Settings > Thresholds > Compressor to Aux Runtime, which sets the “maximum number of minutes running the compressor before engaging the auxiliary heat.” If you set this too low, the heat pump may not have a chance to get up to temperature before turning on the auxiliary heat.