Today, as I write this blog post, we are forecast to set cold temperature records in much of the USA. Here in Atlanta, it’s a cold, cloudy & damp 40 degrees this afternoon… UGH!
Here’s a question I get asked many, many times.
“Why isn’t my house warm? We have plenty of insulation and double-pane windows, but the furnace runs and runs, … and the air doesn’t feel real hot coming out of the vents!”
AC vs HEAT
With AC, you either have it or not. There is a compressor and refrigerant. If your refrigerant charge is too low or too high, the performance falls off, and the airflow temperature suffers, (blowing warm air out the vents).
But with heat, there are different technologies. What kind of heat do you have?
Let me say right here, I am not a licensed HVAC pro. And the purpose of this article is not to be technologically “sound”. The purpose of this article is to help you understand why your home may be chilly or uncomfortable, even though the ‘heater is running’.
If your house is total electric, you definitely don’t have a gas furnace. There are two basic types of electric heat (for residential) that we see in our market:
HEAT PUMP In my experience, this is the most popular form of electric heat that we see in homes. Basically, this system uses the existing AC compressor that is run “backwards” with a reversing valve, when you flip the thermostat to ‘heat’.
This may be hard to understand, but a heat pump (when in the ‘heat’ mode) is actually removing the heat from outdoors, and ‘pumping’ it into your home. On mild chilly days, they work fine. But on days where the outdoor mercury is below 40 degrees, heat-pumps meet their limitations.
I am told, by design, a heat-pump can provide about a maximum 40 degree difference in temperature between the outdoor temperature and the airflow temperature. And, in 18 years of business, I’ve found this to be pretty true.
If it’s 40 degrees outside, the heat-pump is giving you (at maximum) 80 degree heat. If you have the thermostat set at 78 degrees, you can see why it will never shut off, until the outside temp raises, or you lower your thermostat.
Not only that, but the airflow feels ‘cool’, because it’s 18 degrees cooler than your body temp.
On those really cold days & nights, just add 40 degrees to the outside temp, and you see why your heat-pump is struggling, and why your house feels COLD!
ELECTRIC STRIP Do you have a hand-held hair dryer? Those wires that are glowing red are called electric strip or “resistant” heat. Those wires resist the flow of electricity, and therefore heat is produced as a by product. Much like the incandescent light bulb.
Use a fan to blow air across the heat strips, and you have electric heat. In fact, heat-pump manufacturers put these heat strips in their units. When you flip the thermostat to “aux-heat”, or “emerg heat”, you are using the heat strips to further heat the airflow coming from your heat-pump. Those auxiliary heat strips raise the airflow temperature a few degrees.
Heat strips are also found in baseboard heating and space heaters. They come in all shapes and sizes! One thing about electric strip heat: the heat strips will lose efficiency over time, and cost you more money in “electricity used” compared to “heat delivered”.
The picture in this article is a vent in our small north Georgia vacation home. It is total electric, and uses electric strip heat with the central AC unit. On a recent very cold winter day, you can see the airflow temp is a toasty 130 degrees!
GAS FURNACE Here in Atlanta, this is by far the most common form of residential heating we see. Regardless of the efficiency of a gas furnace, the heat output is pretty similar across all gas furnaces. Expect the temperature of airflow to be in the mid to high 120 degree range. There are safety relays that “limit” the temperature from hitting extreme ranges.
Recently, heat pump manufacturers have designed “dual fuel” heat pumps. When outdoor temperatures drop below a certain ‘set point’, the heat pump is supplemented with gas heat. In my experience, the set point for dual-fuel heat pumps in our area is 40 degrees.
If your gas furnace is “cycling” on and off repeatedly, in short cycles, it may be due to the heat limit relay protecting the unit from overheating.
So, who has the warmest heat?
The electric strip heater is a top performer, although it’s the most expensive heat, in terms of the cost of electricity. It’s important to monitor the age and efficiency of the heat strips.
The gas furnace is also a top performer. They are dependable, reliable forms of heat and natural gas costs are very reasonable.
The heat pump has a place on cool or chilly days and nights; but not a true performer when it’s cold outside, and you want to feel heat coming from your vents! Add the supplemental heat strips or gas furnace option, and the heat-pump usually catches up. Where we see heat pumps failing to satisfy a homeowner is when the heat strips are worn out or when a technical issue (problem with the defrost mode, etc) exists.
Like I said in my introduction, this article is a very simple overview of three basic types of heat we see in homes across the metro Atlanta region. For more detailed (accurate?) information, you may need to contact a trusted HVAC pro.
Got Questions for Bob? We’re here to help! Would love to hear from you at 404-538-9168 or use Bob@Birdinsulation.com