Heat pumps do not operate as efficiently when temperatures drop to between 25 and 40 degrees Fahrenheit for most systems. A heat pump works best when the temperature is above 40. Once outdoor temperatures drop to 40 degrees, heat pumps start losing efficiency, and they consume more energy to do their jobs.
For this reason, heat pumps start to lose efficiency at around 40 degrees F and become less efficient than furnaces at around 25 degrees F. Heat pumps continue to be effective at cooling the indoors, even at high temperatures. In the South, it rarely gets below 25 degrees.
This heating method works incredibly efficiently until the outdoor temperature reaches about 35 degrees. At this point, the heat pump has difficulty extracting enough heat from outside to keep up with the thermostat setting. This is when many people assume it's time for switching their heat pump to emergency heat.
Most standard heat pumps will function at 100% efficiency until the outside temperature reaches about 40° F. However, when the temperature dips below this, most heat pumps are not able to maintain efficiency. They become much less effective at temperatures between 20° F to 30° F.
Below 40° f or 5° C the heat pump will frost up and need to turn off to allow the exterior unit to melt. The thing is though, about 10 years ago or longer, heat pumps started to have four-way valves that would switch between cooling and heating.
People do not need to turn their heat pumps off. Residents should make sure their supplemental home heating systems are on and operating. Set the thermostats to a degree or two lower than heat pumps.
It states that the control for the lockout temperature shall have a maximum setting of 40 degrees F, and set for 32 degrees or less at final inspection.
With a typical operation of a hybrid heating system, the heat pump will operate with ambient temperatures above 32 degrees. When temperatures are below 32 degrees, the gas furnace will operate.
Once you understand how a heat pump operates, we can explore some possible reasons why a heat pump might blow cold air, such as incorrect thermostat settings, clogged air filters, a dirty outdoor unit, or issues with the reversing valve.
Heat pumps do not operate as efficiently when temperatures drop to between 25 and 40 degrees Fahrenheit for most systems. A heat pump works best when the temperature is above 40. Once outdoor temperatures drop to 40 degrees, heat pumps start losing efficiency, and they consume more energy to do their jobs.
Frost and ice shreds may also collect around the heat pump. However, if extreme amounts of ice and snow buildup over the unit, it's strongly recommended to switch it off or to 'emergency heat' to remove the snow. The easiest way to get the snow off the heat pump is by pouring warm water over time.
It's Defrosting
To protect the outdoor coils from freezing up in the winter, heat pumps go through a defrosting period every hour or so in which they are truly blowing out cold air. This defrosting period only lasts a few minutes and should not affect the overall temperature of your home.
It also serves as a secondary heating system that can switch on if your heat pump isn't able to maintain your desired indoor temperature. Most heat pumps will turn on emergency heating mode automatically when conditions require it.
If the temperature is too low, ice may have gathered on the device. This obstructs airflow and prevents heat absorption. Usually, heat pumps have defrosters which help alleviate this problem. If the defrosters are active, this should be enough to fix the problem.
Auixiliary Heat will turn on automatically when heat can no longer efficiently transfer heat from the outside air to heat pump. This is when the outside is around 35-40 degrees and the indoor temperature is around three degrees cooler than the thermostat setting.
The break-even point is usually around 15 degrees. Your heat pump will still work below freezing and below 15 degrees. It will continue to perform below 0 degrees or colder. It just won't be as efficient over those very coldest days of winter as using a gas-fired furnace.
Heat pumps tend to start losing efficiency when the temperature of the air around it drops below 40 degrees Fahrenheit. At 25 degrees Fahrenheit, a heat pump becomes so inefficient that it is less effective than a standard furnace.
Short answer: No. Switching your thermostat to emergency heat or “em heat” just because it's cold outside will just raise your energy bills like crazy. Don't use emergency heat mode unless your heat pump stops heating your home altogether. If that happens, contact a professional heat pump repairman for help.
Rebate-eligible heat pumps can reach over 400% efficiency in mild temperatures and can maintain well over 200% efficiency even into negative temperatures. This is why turning off a heat pump in frigid temperatures and opting to use a fossil fuel boiler or furnace instead is a mistake.
“Auto” mode could cause your heat pump to heat on a cool summer night or cool on a sunny fall or winter afternoon. To avoid accidentally cooling during the fall and winter, use “Heat” mode. Likewise, to avoid accidentally heating on a cool summer night, use “Cool,” “Dry,” or “Fan,” but not “Auto.”
Avoid shrubs, places prone to snow drifts, and structures that might block airflow. It's also important to make sure outdoor units aren't blowing onto one another. Door, window, and walkway interference — It's best to avoid installing the outdoor unit where it could interfere with the operation of a door or window.
If there is not enough refrigerant in your system, it can't absorb as much heat. As a result, the coil may freeze if the outside temperature drops below 32 degrees Fahrenheit. Furthermore, as your heat pump naturally ices up in cold temperatures, there may not be adequate refrigerant to defrost the heat pump.
Know your temperatures
There is a middle point that'll help you with both. Set your heat pump temperature to 18 degrees or above to help fight damp and mould, but below 21 degrees to save on power. The higher the temperature, the more energy the heat pump will use, so anywhere between 18 and 21 is the sweet spot.
When the outdoor coil temperature drops to around 32° F, the thermostat closes the circuit and makes the system respond. This causes an internal timer to start. Many heat pumps have a generic timer that energizes the defrost relays at certain intervals of time.