Should I close the door when running AC in fan mode

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SUMMARY

The discussion centers on the effectiveness of running an air conditioning unit in fan mode while considering whether to keep the door open or closed. Participants confirm that fan mode only circulates indoor air and does not introduce outside air. Opening the door to the outside may allow outside air to enter, but the impact on airflow is minimal due to the presence of a wall and the lack of windows in the room. Factors such as temperature and humidity are crucial for determining the benefits of opening or closing the door, especially as conditions change throughout the day.

PREREQUISITES
  • Understanding of HVAC systems and their modes, specifically "fan mode."
  • Basic knowledge of airflow dynamics and pressure differences.
  • Familiarity with temperature and humidity effects on indoor air quality.
  • Awareness of tools like SimScale for simulating airflow scenarios.
NEXT STEPS
  • Research the principles of HVAC fan modes and their impact on air circulation.
  • Learn about airflow dynamics and how pressure differences affect air movement.
  • Investigate the effects of temperature and humidity on indoor air quality.
  • Explore SimScale for simulating airflow in different room configurations.
USEFUL FOR

Homeowners, HVAC technicians, and anyone interested in optimizing indoor air quality and understanding the implications of air circulation in confined spaces.

Altiano
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I have a 3x3.5 (meters) room with a bathroom of approximately 1.5 x 2.
I want to know whether to close the door or not, If I running Fan Mode.
There is wall in front of my door, about 60 cm,

My assumption: Fan mode only circulate the air, If I open the door, I'll bring outside air in, which is better than just inside air
 
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I have not heard before of a fan mode in a bathroom.
In my own bathroom there is an extractor fan; the fan goes on when the light is on,
(that is, somebody is using the bathroom)
Opening a door or closing it will not make a lot of difference to the flow of air.
Air is gases; gases flow from higher pressure to lower pressure and solid objects usually don't stop it. gas finds a way around it.
 
Last edited:
Altiano said:
I have a 3x3.5 (meters) room with a bathroom of approximately 1.5 x 2.
I want to know whether to close the door or not, If I running Fan Mode.
There is wall in front of my door, about 60 cm,

My assumption: Fan mode only circulate the air, If I open the door, I'll bring outside air in, which is better than just inside air
There are some things that aren't clear to me, but I'll give this a shot:
1. Yes, "fan mode" just re-circulates. It does not bring in outside air.
2. What door are you opening? Door to outside or door to bathroom. If it is the door to the bathroom, I don't see why outside air will come in. If it is the door to outside, sure, air will come in, but your system's "fan mode" won't affect that.
3. Sometimes bringing in outside air is useful and sometimes it isn't.
 
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Your OP doesn't mention temperature or humidity at all (inside or out) so really impossible to know what you are trying to achieve.

Where I live opening an outside door is currently a bad idea, but in 5-6 hours it will be a fabulous idea, I can't wait.
 
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russ_watters said:
There are some things that aren't clear to me, but I'll give this a shot:
1. Yes, "fan mode" just re-circulates. It does not bring in outside air.
2. What door are you opening? Door to outside or door to bathroom. If it is the door to the bathroom, I don't see why outside air will come in. If it is the door to outside, sure, air will come in, but your system's "fan mode" won't affect that.
3. Sometimes bringing in outside air is useful and sometimes it isn't.

Okay, I'll try to explain a little bit more of the room,
- There are no windows in the room
- What I open is the door to the outside
- Not really "outside (like open field)", because the room is in the (boarding) house.
- In front of that door is a wall, on the right about 20cm, is a window.

Actually I am curious to know what are the benefits for opening the door and closing the door when running on "Fan Mode".

CWatters said:
Your OP doesn't mention temperature or humidity at all (inside or out) so really impossible to know what you are trying to achieve.

Where I live opening an outside door is currently a bad idea, but in 5-6 hours it will be a fabulous idea, I can't wait.

Just want to know what will happen in 5-6 hours? :)
 
Altiano said:
Just want to know what will happen in 5-6 hours? :)

The sun sets and it gets cooler outside than inside.
 
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If you want to go for an overkill solution, you can try and simulate it with SimScale. There are examples that are similar to yours like the airflow in an office space.

You can get sign up and create a free account and try things.
 

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