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If your HVAC and air pressure systems are balanced, it should not matter if the basement door is open or closed in winter. If the system is unbalanced (negative pressure in basement), hot air will be pulled down to the basement. Close the door to keep heat in the basement.
The basement is known as the coldest place in the house for various reasons. That being said, how much does the basement’s temperature affect the rest of the house, and does the door being opened or closed limit the effects?
This article explores not only air temperature but also air pressure systems and how they affect your home. You’ll learn whether your basement door should be open or closed, how to keep your energy bill low, and how to solve temperature-related problems.
Shouldn’t Matter if System Is Balanced
The air pressure system in a house has to be balanced for the HVAC system to function optimally and for the inhabitants to have the full benefit of the HVAC system.
Scientifically speaking, it is unlikely for an open door of a basement to rapidly cool down the entire house since hot air rises and cold air sinks. This is especially true of a balanced system.
Air molecules expand as they heat up, making the air less dense. This decreasing density causes hot air to be less dense than the air surrounding it so that the hot air rises.
Cold air does the opposite. The air’s molecules contract and become denser as they cool down, causing the cold air to sink.
With these facts in mind, the cold air from the basement should sink and stay in the basement while the warm air from the home will rise and stay out of the basement.
What Happens if the System Is Not Balanced?
When your HVAC system is not working at its best, a low-pressure system can form in your basement. Just like when talking about the weather, air favors moving from a high-pressure system to a low-pressure system.
This means that air flows towards a low-pressure system, and in the case of a low-pressure system in a basement, the warmer air from the rest of the house will flow towards the basement. This is not what you want in winter!
Also, if the basement has a low-pressure system, higher pressure air outside will be pulled into the house through any surfaces that aren’t perfectly sealed.
When the air needed to warm the rest of the house is pulled into the basement, your HVAC system will be required to work harder to maintain a stable temperature. Also, when cold air is being pulled into the basement, the HVAC system must work even harder.
With your HVAC system working harder than it should, your electricity bills will rise.
Easily Check Your Home’s Pressure System
To check if you have negative pressure in your home, this can be done with very precise but expensive instruments or with simple observations.
There are a variety of instruments for measuring pressure. One is a manometer, which is a highly precise and expensive instrument. At its best quality, a manometer is around $1,000. But you don’t have to buy the high-end option.
- SMART DUAL INPUT – RISEPRO® manometer can easily measure the differential pressure with its dual input probes.
- RANGE & RESOLUTION – Measures +/- 2.000psi (0.001 resolution) with accuracy +/-0.3% in full scale
- MAX PRESSURE – 10psi (Can resist up to 10psi but may not show readings when over 2psi)
- 11 SELECTABLE MEASURE UNITS – InH2O, Psi, Mbar, kPa, inHg, mmHg, ozin2, FtH2O, cmH2O, KGCM2, Bar
Another kind of pressure-sensing instrument is a Magnehelic gauge. It is much less expensive (under $100) but not as great of quality.
This test doesn’t cost any money. All you have to do is, if you are testing your basement, go inside your basement and face your basement door.
Open the basement door a couple of inches and put your face near the opening.
If you feel air on your face (entering the basement), then there is a negative pressure system in your basement.
Furthermore, if the airflow is sufficient, the door will be shut by this downward flow of air.
How to Rebalance the Pressure System
Problems resulting in an unbalanced pressure system can be as simple as shut interior doors or as complicated as various combustion appliances contributing to the issue.
If these efforts do not yield a balanced pressure system, then it might be time to consult an expert. This could be a furnace, HVAC, or air conditioning technician.
Ducts and Vents
Since ductwork and vents are the fastest at circulating air through the house, they are a great place to start with assessing how to fix an air pressure problem.
It is a good idea to check your ductwork for leakage since air leakage leads to higher energy bills as well as negative air pressure.
Also, not having enough supply and return vents to the basement, or the correct ratio of the two, would lead to air pressure problems. You do not want to close all of your return basement vents in an attempt to stop cold air from entering the system). Nor do you want to close your supply vents to stop warm air from the system from entering the basement.
For this issue, it might be best to consult a professional.
Constantly closed interior doors can contribute to the pressure system problem by not allowing air to circulate through the entire house. The cracks between doors and their door frames do not let an ample amount of air in.
It is best to try to keep most interior doors of your house open at least part of the day. This can be experimented with to see if this fixes the problem.
Furnaces can negatively impact your home’s pressure system since their discharge (draft) creates negative pressure conditions. They could be the source of your problem, so it is best to consult with a furnace expert if you suspect your issues are stemming from your furnace.
Finished vs. Unfinished: Does It Make a Difference?
Since an unfinished basement would not only have less insulation in the walls and ceiling but also in the flooring as well, it would be colder than a finished basement. A freezing concrete floor vs. a carpeted or wooden one would make all the difference in the temperatures of a basement.
If the concern for the rest of the house is that the basement is a low-pressure system and warm air from the rest of the house will enter the basement, it doesn’t make a difference if the basement is finished or unfinished, the difference in temperature wouldn’t affect the low-pressure system.
As far as opening or closing the basement door during the winter, as long as the pressure system is balanced, it should not make a difference to the rest of the house.
However, if you have a finished basement and you are trying to keep it warm, you should close the basement door to prevent the passive rise of hot air up and out into the main floors of the house.
Basement Not Part of HVAC System
Assessing the ductwork and vents as discussed above would only be useful in a scenario where the basement is actually a part of the HVAC system. This might not be the case for you, though.
In this case, closing the basement door would be beneficial. The heat generated in the basement, for example, by a space heater, would stay in the basement for the most part with the door closed. The rest of the house would not be affected by the basement’s air.
Nonetheless, it is still very important to have balanced pressure systems in your home. Also, although the basement does not need to be a part of your HVAC system, it must still be ventilated.
Sometimes, keeping the basement door open or shut has more to do with how in-the-way the open door is, which depends largely on the swing direction of the basement door.
Related article: Basement Door Open or Closed During Summer
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