If everything is working properly, the air coming out of your furnace will be about 40° – 70° warmer than the air coming in; this increase is called the temp rise. If the temp rise is too high, it could be caused by an oversized furnace, undersized ductwork, a combustion problem, or an airflow obstruction.
Every gas furnace data plate/tag has a specification for the temperature rise through that furnace. It is shown in a range like 50-80° or 45-75°. Those first two numbers are the lowest recommended temperature rise; the highest allowed temperature rise through the furnace is usually a 30° difference.
Temperature Differences Between Inside and Outside Air
Generally speaking an air conditioning system is designed to accommodate up to a 20 degree difference between the outside air and inside air while still keeping around a 55% humidity level which is comfortable.
While there are occupants in the house, it is advised for homeowners to set their thermostats between 68 and 72 degrees to promote maximum comfort. A pleasant temperature for everyone in the house, regardless of the apparel they are wearing, is between 68 and 72 degrees, which is neither too warm nor too cool.
Temperature fluctuations throughout a furnace can be caused by its different characteristics, including insulation thickness, position of furnace openings, air distribution, volume of airflow, control accuracy, and construction techniques.
If the furnace is running but blowing cold air, there can be a number of things that have gone wrong, from a change in thermostat settings and a filter that needs changing to a pilot light being out and sensors being dirty.
Under or Over-sized Systems
If you have an improperly sized AC system for your home, this can result in a temperature imbalance. If your AC system is too big, it will shut off quickly, leaving some rooms too cold or warm.
There may be drafts and pockets of colder air near the floor; The walls are colder and don't emit the usual amount of infrared radiation, so you lose heat due to your body emitting more IR than it receives; You may spend more time indoors and hence have less physical activity, so your body generates less heat.
Sleep experts believe the best temperature for great sleep is between 68-72 degrees Fahrenheit. But in addition to making you uncomfortable and interfering with healthy sleep patterns, being too hot at any time of day or night can cause health risks like dehydration and heat stroke.
If you're cold even though your thermostat indicates you shouldn't be, your furnace likely isn't the problem. In most cases, it's working just fine. It's your home that needs attention. Lack of insulation, severe air leakage, and/or unbalanced ductwork are frequently to blame.
For many of us, 70 degrees is the ideal indoor temperature, but when it is close to 100 degrees outside, your AC unit will be working quite hard to meet these expectations. Consider setting your thermostat at 75 degrees to 80 degrees in your home if the outside temperature is approaching triple digits.
First, check your filters and coils for dirt and debris that may be impeding airflow. Once you've cleaned the filters and coils, run the air conditioner with just the fan so that the ice accumulation can melt off. If the AC still doesn't blow cold air, it could be that refrigerant levels are too low.
Simply put, it means you should never set your thermostat for a temperature more than 20 degrees cooler than the outside air. Why not? Most air conditioning systems can only handle a 20-degree difference between the outside and inside air temperatures.
A furnace that's running non-stop is not necessarily bad. During the coldest days in winter, it is normal for a furnace to run almost constantly to keep the home warm.
Keeping your home at a balmy, tropical temperature may feel nice, but it won't feel so nice when the bill comes. Most recommend keeping your furnace between 68 and 70 degrees. You will find that after about a week at a lower temperature, your body becomes accustomed to it, and it no longer feels cold to you.
However, it's best to have a 16 to 22°F difference between your supply air and return air temperature when you set your thermostat. HVAC professionals call this the “evaporator Delta T.” When a temperature difference is within the Delta T, your AC is working properly.
The best room temperature for sleep is approximately 65 degrees Fahrenheit (18.3 degrees Celsius). This may vary by a few degrees from person to person, but most doctors recommend keeping the thermostat set between 65 to 68 degrees Fahrenheit (15.6 to 20 degrees Celsius) for the most comfortable sleep.
The Short Answer Is: Homeowners can typically set their thermostat to a safe and comfortable temperature during winter, aiming for around 68 to 72 degrees Fahrenheit when at home.
The World Health Organization (WHO) recommends setting your thermostat no lower than 64 degrees (F) in the Winter months while people are in the home. If there are infants or elderly individuals, they recommend keeping the temperature at 70 degrees at a minimum.
If your furnace is blowing hot but your home is still cold, it may be a problem with your ductwork. You may have leaky or damaged ducts that are letting hot air escape and cold air in. Sometimes a damper in the system can get miss-adjusted or come loose, thereby inadvertently blocking or reducing airflow.
Many seniors find 78 degrees to be the most comfortable indoor temperature. Anywhere from 65 to 78 degrees is considered safe.
What Is an Acceptable Temperature Difference Between Rooms? Rooms on the same floor of your house should be roughly the same temperature. A difference of 1–3 degrees is to be expected, although 3–5 degrees isn't outside the realm of possibility.