# Heat loss through an open door

• James Allsopp
In summary, the conversation discusses heat loss through windows and doors and the energy wasted when store owners keep their doors open in winter and summer. The speaker provides a rough estimation of the air leaving through the doorway and the amount of energy lost. They also mention a solution of using a blower to reduce heat loss while keeping the door open.
James Allsopp
All the info I could obtain talks about heat loss through windows and doors. I am trying to get
several store owners in my town to close there doors in the middle of winter and summer.
The average door is 28 sq ft. I am assuming the inside temperature is 68 degrees and the outside temperate is 34 degrees. How much energy are they wasting? This is not a homework question. I am 65 years old. Too old to remember any of my physics.

Interesting application- here's a back of the envelope estimation:

Assume all the heat loss is through air loss: heated air leaving the store. The specific heat of air is about 0.001 J/(cm^3*K) (from wikipedia). What's the amount of air leaving through the doorway? 28 ft^2 is about 27000 cm^2, estimate a 'wind velocity' of 1 m/s with the door open gives about 3*10^6 cm^3/s air leaving the store. The air is heated 30 degrees, this gives 9*10^4 J/s (9000 Watt) energy loss.

That seems like a lot, so double-check my calculations- I did them in my head.

That seems reasonable to me. At 10 cents/kWh that is only about \$1/hour, so I could see how a business owner might think that an open and inviting door is worth that cost.

Andy Resnick said:
Interesting application- here's a back of the envelope estimation:

Assume all the heat loss is through air loss: heated air leaving the store. The specific heat of air is about 0.001 J/(cm^3*K) (from wikipedia). What's the amount of air leaving through the doorway? 28 ft^2 is about 27000 cm^2, estimate a 'wind velocity' of 1 m/s with the door open gives about 3*10^6 cm^3/s air leaving the store. The air is heated 30 degrees, this gives 9*10^4 J/s (9000 Watt) energy loss.

That seems like a lot, so double-check my calculations- I did them in my head.

1 m/s sounds quite high velocity-it's 36 KM/Hr, I don't think I feel such strong wind when I'm standing at the door.It sounds more like a free convection problem then a forced convection. But there are some other solutions,in some malls I saw a blower installed above the door, the air flow from the blower creates an "air screen" which reduces the heat losses, on that way they can keep their door open and still reduce the energy wasting.

## 1. What causes heat loss through an open door?

Heat loss through an open door is caused by the movement of air from a warmer area (inside the room) to a cooler area (outside). This movement of air, also known as convection, carries heat away from the room and can result in a decrease in temperature.

## 2. How does heat loss through an open door affect energy efficiency?

Heat loss through an open door can significantly impact energy efficiency. It can result in increased energy consumption as the heating system works harder to maintain the desired temperature. This can lead to higher energy bills and a decrease in overall energy efficiency.

## 3. Does the size of the door affect heat loss?

Yes, the size of the door can affect heat loss. The larger the door, the more air can pass through it, resulting in a greater amount of heat loss. This is why it is important to properly seal and insulate doors to minimize heat loss.

## 4. How can I prevent heat loss through an open door?

To prevent heat loss through an open door, you can use weatherstripping and draft stoppers to seal any gaps around the door. Installing a storm door can also help to reduce heat loss. Additionally, closing the door quickly and minimizing the amount of time it is open can also help to prevent heat loss.

## 5. Does the material of the door affect heat loss?

Yes, the material of the door can affect heat loss. Materials that are good conductors of heat, such as metal, can result in more heat loss compared to materials that are good insulators, such as wood. Investing in a well-insulated door can help to reduce heat loss through an open door.

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