With the heating season approaching I wanted to cover some common concerns, myths, and what to expect with heat pumps. Every year we get calls about heat pumps making funny noises, smoking, and even burning smells all of which can be normal so I wanted to get a blog out there talking about this before the season hits. Whether you've owned a heat pump for many years or if it's your first year with one, I think all will find something new in this blog that will shed some light so I hope you enjoy.
The number one call that we get is "I smell a burning smell coming from the unit so I turned it off". This can be something serious as well as it can also just be a sign of lack of maintenance. Most heat pump installations (especially in homes) have electric resistive heat strips in them to assist with extremely cold temperatures or high heating demand. The electric heaters are typically only used in the winter so all spring, summer, and fall (in easter North Carolina) they just sit in the air stream collecting dust. The first time these get turned on they can burn that dust off generating a burning smell throughout the home and indeed something is burning. This can be avoided by having a service professional perform a tune up prior to the heating season where they should be pulling the heat strip and cleaning it before allowing it to run. At the same time, they should be inspecting the heating performance for safety and reliability which is always a nice piece of mind. Another and more serious cause of burning smells can be and often is either windings of a blower motor burning up or lose electrical connections getting too hot and causing something to burn in the air handler. This does happen and much too often, so it's always a good idea to have a qualified professional inspect these systems to ensure they are safe and reliable. I can't stress that enough, it always scares me (for the occupants and their pets) when I go to an air handler and see that there's been a fire inside of the cabinet. Even if you have new equipment, electrical connections can become lose do the vibration of the equipment as well as the changing of temps surrounding the equipment. Think about an air handler that sits in the attic, that attic goes from hot to cold hundreds of times per year. The electrical conductors are metal which expands and contracts with the changing of temperatures. This can cause even new installations to have lose connections and ultimately lead to an issue with overheating components.
Another call we often get is "the outdoor unit made a metal grinding noise and smoke came out the top so I shut it down". This is perfectly normal and requires no action at all as this perfectly describes the defrost cycle of a heat pump. A heat pump is going to form rings of frost/ice at times on the outdoor unit in lower ambient temperatures, to which the heat pump will periodically go through a defrost cycle. In a defrost cycle the outdoor coil should get hot enough to melt all the ice (during which time the outdoor fan motor will not be turning) and when the system is done it will abruptly reverse the flow of refrigerant (generating some alarming grinding noises) and the outdoor fan will all of sudden start running. When the outdoor fan commences to run, there can be a large puff of "smoke" (actually its water vapor) shoot out the top of the unit as it goes back into a normal heating operation. This already addresses another call we get which is the ice build up on the outdoor unit. It's perfectly normal for ice to develop on the outdoor coil, so long as that specific ice melts off at least every 1.5 hrs of operation. In extremely cold temps ice can form in a very short period of time on this coil so if you are concerned about the defrost cycle working properly or not, either sit there and watch it for 1 hour of run time or put a camera on it (if this gives you a piece of mind and you don't want to pay a service fee), if the unit goes through the sequence I described above, you should be good to go.
We often get a call about "emergency heat/auxiliary heat" running and if that is a concern. The answer to that is yes and no. These two terms sometimes get confused while technically speaking they are supposed to be differentiated, they both control the same function. This type of heat is that electrical resistive heaters I mentioned earlier. These heaters are not as efficient as a properly working heat pump and their use should be minimized. A unit can be forced into emergency heat when the heat pump is not working properly and this is usually done at the advise of a service professional after an issue with the heat pump has been identified. Auxiliary heat will show up on a thermostat under a few conditions. Many basic thermostats are designed to bring on the auxiliary heat when the demanded heat setting is set more than 2 degrees above the indoor temperature. Lets say it's currently 65 in your home and you want it to be 70, then the average thermostat will engage both the heat pump and the auxiliary heat to achieve this demand. Smart and wifi thermostats have the ability to use outdoor temperature to lock out the auxiliary if we know it may not be necessary. Often times we set the lockout at 35 degrees (unless the actual balance point is known) meaning that anytime the outdoor temp is above 35 degrees, the auxiliary heat will be disabled and the thermostat will only allow the heat pump to heat the home regardless of demand. That's especially handy in terms of keeping the electric bill down since the auxiliary heat has a COP or coefficient of performance of 1 and a heat pump is often higher than that. The COP tells us how much energy we get out of something vs the amount of energy we had to supply to it. Basically, a 1 is ok, but if we can do better than 1 we save money and a heat pump above the balance point will always supersede 1.
The last major call we get especially from clients who are not used to heating with a heat pump is that the air coming out of the vents is cold. It feels cool to you, but if you were to measure the temp of the air you would see that it's above the indoor temp meaning that it's warming the home. This happens because humans in general think of warm as usually anything between 90 degrees and 115 degrees. Makes sense seeing as our body temp is generally around 98.7 or so. In a home with an indoor temp of 70 degrees, the air coming from the vents can be 78 degrees or higher. Now 78 degree air wont feel warm to me especially when it's 30 degrees outside, but keep in mind that 78 degrees is higher than 70 degrees, which means the air generated by the heat pump is still warmer than the home and therefore is heating the home. Those specific numbers would be a sign of a higher efficient system operating in a low stage, typically single staged equipment or equipment at full capacity with an indoor temp of 70 will have a supply air temp around 90 (+/- 7), which is still not going to feel "cozy warm", but it's perfectly normal.
Understanding your equipment can save you not only money, but headache as well. Calling a service company when not necessary will almost always end up costing you at least a service fee. Before that happens, it's a great idea to get your system inspected and ready for that chilly whether. Work with your provider especially if you have a smart thermostat, and see if you can lock out that expensive heating bill by trying to dial in the balance point and really maximize the energy saving you already have control of. I have found that in eastern North Carolina our average balance point is about 17 degrees. I actually have been running the last 4 years with no auxiliary heat and aggressively sized equipment and my home has always been perfectly comfortable without compromise.
Kenneth Casebier
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