HVAC Hacks: Tips for Novices and New Homeowners

Can Your Geothermal Heat Pump Stand Up Against Old Man Winter?

Making the switch from a conventional heating and cooling system to geothermal climate control is a big deal for many homeowners. So it's not surprising for some homeowners to wonder how their brand-new geothermal system will stand up under harsh winter conditions. Some may even worry that their heating system's performance will fall flat under extreme cold.

The following helps dispel a pervasive myth surrounding geothermal heat pumps and their wintertime performance. You'll also learn what to expect when operating your energy-efficient heating system when temperatures dip below freezing.

How Geothermal Heat Pumps Work

Unlike traditional furnaces that rely on fossil fuels, geothermal heating systems tap into a more eco-friendly and conveniently located source of energy—the very earth itself—to provide heat for your home. Instead of harvesting thermal energy from the surrounding air like a typical heat pump, however, geothermal units harvest their thermal energy from the ground.

The thermal energy taken from the ground is then transferred via an underground piping loop to the indoor unit. Like air-source heat pumps, the heat-absorbing fluid serving as the unit's transfer medium is compressed and circulated through a heat exchanger, allowing the unit to shed heat into your home. The cooled fluid returns through the ground loop to absorb more thermal energy.

How They Perform Under Harsh Cold

Many misconceptions about geothermal heating performance come from observing how air-source heat pumps perform in cold weather. Most air-source heat pumps suffer a dramatic drop in efficiency and temperature output as temperatures fall below freezing. The colder the surrounding air gets, the less thermal energy is available for the heat pump to effectively harvest.

While air temperatures can plummet below freezing for extended periods, ground temperatures usually remain stable. Temperatures at the outer fringes of the earth's surface—the upper 10 feet—typically hover around 50 and 60 degrees Fahrenheit. These constant temperatures allow geothermal heat pumps to perform well under conditions that would cause problems for their air-source brethren.

Geothermal heat pumps remain effective sources of whole-home heating as long as ground temperatures remain above 45 degrees Fahrenheit. Even in very cold climates where the first few feet of ground occasionally freezes, geothermal systems can still offer impressive performance and efficiency. It's only in areas where ground freezing happens for extended periods that other, more robust types of heating systems should be considered.

When Supplemental Heat Is Necessary

Air-source heat pumps often need a supplementary source of heat, also known as "emergency heat," to tide users over when extremely cold temperatures result in reduced heating output. These supplemental heating sources usually consist of electric heating elements, although natural gas and oil burners have been used for backup heat.

Each heat pump system has its own threshold for activating its supplemental heat source, but most systems activate when temperatures dip well below freezing, when there isn't enough thermal energy for air-source heat pumps to extract heat efficiently. Geothermal heat pumps rarely encounter the above situation since these units extract their thermal energy from a stable source.

In short, a well-designed geothermal heat pump generally won't need a supplemental heating source. However, you may feel better about having a backup system in place for very rare occasions where your home's heating system could use an extra boost. Just keep in mind that actually using your backup heat can cause a significant increase in your next month's utility bill.

Variables to Consider

Geothermal heat pumps are just as capable of tackling extreme winter temperatures, but only if they're designed and installed properly. Variables that can affect successful geothermal HVAC operation include the unit's size and capacity, the type of loop system used, and even the quality of the installation itself.