Trapped Ceiling Heat





Introduction: Trapped Ceiling Heat

About: I like to tinker, That is what I like to do. Sometimes I drop a rhyme, Along with a tool or two. I use what I have on-hand, I keep projects super simple. I do not need more stuff, What I do have is ample. Dr...

Baby it's cold outside.... The thought of heating my house makes me warm under the collar.  I have a forced hot air heating system.  I have been researching ways to make improvements or modifications to increase the efficiency.  This past winter I took a close look at heat trapped at the ceiling. 

There is usable heat trapped at the ceiling.  During my research I can not count how many articles I read stating the aforementioned presupposition.  I was excited to cash in or at least benefit from that statement.

If I move the heat from the ceiling, I can raise the overall room temp.

How much heat was trapped at the ceiling?
What would be the best way to move the heat from the ceiling down to the comfort zone?
Is it cost effective to pull that heat down and warm the overall room?

Let’s look at my results.

Step 1: Equipment

Acu Rite Wireless digital thermometer

Step 2: Test Procedure

Measure the temperature at 3 point in the living room; Ceiling, Mid and Floor for a week. 
The temperatures were recorded for 6 hours during the night, between 6 PM and 12 AM midnight, after the furnace turned off and every hour. 
We use Compact Florescent Light bulbs and the TV operates from around 8 PM - 11:20 PM. 
The ceiling is 8 feet high.

Ceiling – wireless sensor 1” (1 inch) from the ceiling.
Mid – digital thermometer 4’ (4 feet) from the floor.
Floor – digital thermometer 1 - 2” (1- 2 inches) from the floor.

Constant: Thermostat temperature set at 64F.  The Furnace turns on 1 degree below and turns off at 2 degrees above the set temperature.
Independent Variables: Ceiling temperature, Mid and Floor.

Note: The bracket holding the sensor is the bracket I made with my Impromptu Sheet Metal Break Bender.

Step 3: Analysis

Here is a summary of the data after a week of collecting.

Constant: 64F
CeilingAverage: 66.65F
Mid Average: 66.65F (the same average as the ceiling)
Floor Average: 62.77F

The Ceiling and Mid section of the room did not see any difference.  Furthermore there was less than a 4 degree difference between the Ceiling / Mid section and the Floor.  Nothing to become excited over with the exception of knowing the house is pretty well insulated.  There is no gain from moving the Trapped Ceiling Heat downwards.

Step 4: Observation, Conclusion & Summary

During my research I found a lot of web sites suggesting to run the ceiling fan backwards to circulate the trapped ceiling heat around so that you would feel warmer or to reduce the furnace usage.  Some sites made claims as to the disparity of ceiling temperature and floor temperature.  My results did not show such a variance.

After reviewing the results I did not pursue moving or circulating the Trapped Ceiling Heat.  The aforementioned results did not support my Hypothesis: "If I move the heat from the ceiling, I can raise the overall room temp.", because there wasn't much of a difference in temperature.  The cost of moving the air would have outweighed any improvement  to the overall results and / or the air would have cooled down to negate any benefits. 

Your results may differ.  Keep in mind I am heating with forced hot air, perhaps if you heat with wood or force hot water; moving or circulating the Trapped Ceiling Heat may be a viable option.

I am satisfied with the results, but I am disappointed in the concept of reclaiming Trapped Ceiling Heat.

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    23 Discussions

    I understand this is an old experiment of yours and that the results you reached are for your house and area of the world you live in only. I believe that reading through the comments below that some of these people might experience it differently due to either the ceiling heights differences or climate differences. My living room has 9ft ceilings while my entrance has 24ft ceilings and the temp differences are wildly different. The stirring of the air is not felt from the ceiling fans, no wind chill factor, in the winter since they are higher above your head. The fans are running backwards, pulling air against the ceiling, in the winter as compared to the summer time. Just some thoughts as to why some may have different points of view. 4 degrees of temperature swing in 8 vertical feet is not much at all so I'm sure there is no reason to move the air in your situation.

    1 reply

    Thank you for reviewing and commenting. This experiment is still a work in progress. Currently I am working on 2 designs to maintain the heat near the floor so the heat continues to radiate after the forced hot air furnace has shut off.

    There are many factors in determining the best practice for capturing trapped ceiling heat, based upon one’s circumstances. My goal is to do it efficiently based upon actual data. This instructable gave me and others, a starting point to do testing, evaluate the results and draw conclusions. With actual data in hand I moved away from moving the air around to maintaining the heat near the floor. Which I have found to be quite easy.


    2 years ago

    Hi All

    Somewhere in the early 80's we had a guy, ahead of his time, who built a house here in South Africa where he had placed rocks in a cavity under his floor slab(this was featured in a House and Home magazine at the time). He then pumped the hot air from the ceiling into the cavity during the day. At night he could re-use this heat as underfloor heating. This idea was correct because heat in the ceiling is lost very quickly once the sun goes down but is retained much better in rock that is not exposed to the elements

    1 reply

    Thank you for reviewing and commenting. That sounds interesting. He was using thermal mass heating. I wonder how he kept the floor from being hot during the day, unless it took most of the day to raise the temperature of the rocks to make a difference in the floor. Thank you for sharing your experience.

    Nice test.

    The most important thing is that your house (ceiling) has a good thermal insulasion.

    I think that without an insulated ceiling the whole experiment changes

    1 reply

    Thank you for reviewing and commenting. It would interesting to test your hypothesis. Maybe someone would reproduce the experiment and post their results.

    Nice experiment and your results are pretty close to what I would have expected. However, I am not sure that I agree with your conclusion that redistributing the air (mixing the air) would not be of any benefit. Based upon your data I saw a 4 degree difference between your mid and top readings and your floor readings. This is significant!

    It might be just because I am old, but when my feet get cold I get pretty miserable. It reminds me of an old joke about if you stick you head in the oven and your feet in a bucket of ice water, on average your should be comfortable. Unfortunately it doesn't work like that. That 4 degree difference doesn't sound like much, but it is. With the stratification of the room air, you have to raise the temperature in the upper part of the room that much higher in order to get the temperate at the floor to a level where you are not getting frost bite on your toes. In your case, if your feet are indeed comfortable at that average of roughly 63 degrees, then maybe if your mix the air in the room you might be able to lower the thermostat setting down to on average 66 instead of 68, which will actually save a good bit of energy.

    You also mention the cost of mixing the air with a ceiling fan as a factor in not doing it, I can tell you that even if you had a ceiling fan running in every room this would not use near the electricity and energy that running that furnace would. Ceiling fans are very efficient when compared to either the compressor in your central heat system, or whatever other heating medium you are using.

    1 reply

    Thank you for commenting. You make some interesting points. You are correct ceiling fans are more efficient than the furnace fan.

    Ceiling fans are great for moving air. But what happens when you move air over your body? You lose body heat. So during the hot months it is good practice to turn on a ceiling fan in order to remove body heat so you will feel cooler. During the colder month when the wind is blowing, you feel colder; meteorologists call it Wind chill temperature. The Wind chill temperature is affected by how fast the air is moving and the current temperature. So unless the temperature of the air moving is hot or the speed of the ceiling fan is slower then you will feel cooler, because you are disrupting the surface air around your body. There is a balance between the speed of a fan and the temperature of the air.

    I am still reviewing the results. I also do not need to move the air from the ceiling to the floor; because the temperatures are essentially the same, I could simple move the air from the mid section to the floor. It is a work in progress. Again thank you for your comments.

    Thanks ezman, an Interesting post.

    I would be interested to read a similar analysis of a room heated by under floor heating. It seems to me this would be the most energy efficient way to heat a room, especially a large room with high ceiling. I attend meetings in the local Friends Meeting House, which has gas fired boiler feeding conventional radiators around the walls at floor level. In the winter months my thoughts often turn to this question, Why do I feel so cold in this room when the heating has been on for an hour already? I am convinced the heat rises up the walls to the ceiling and does it ever circulate down again? I think a good deal of it probably escapes out of a ventilation opening in the centre of the ceiling.

    1 reply

    Thank you, bbhare. Yes, that would be interesting. I have been analyzing my results and I have postulated that there is heat trapped at the ceiling but it is not restricted to the top 5 inches of the room. In my experiment it maintained the average 64F down to 4 feet from the ceiling. Suppose the ceiling was a cathedral style with the apex at 15 feet. You may find the heat maintained at 4 feet from the ceiling, then dropping off 4 degrees F the next 4 feet and so on? So if we looked at a thermal profile of a room you would see “X” feet at the top with the maximum heat, then the next “X” feet say 4 degrees cooler from the ceiling, the next “X” feet - 8 degrees cooler from the ceiling and again still 4 degrees cooler the last “X” feet. What you have are pockets of heat at different heights of the room.

    As for your question, “Why do I feel so cold…”. Look for drafts around outlets, windows and window frames, baseboards and fix those first. Then look at the dimension of the room, number of and type of windows and doors, insulation of the floor, walls and ceiling. You already noticed the ventilation in the ceiling. After that assessment you can decide where to attack.

    you measured every hour for 18 hours or just for 6 hours ?????

    \6pm till 12am is 18---not clear

    1 reply

    Thank you for reviewing and commenting. Good point it can be confusing when using 12 am and 12 pm, midnight vs. noon. I will make it more clear, by saying the testing was for a period of 6 hrs and add midnight after 12 am.

    Thank you for reviewing and commenting. It would be interesting to repeat this experiment in homes with wood or forced hot water heating systems. I wonder if the creative and resourceful people here at instructables would collaborate to find out the answers with the goal to debunk or prove the internet claims.

    Good instructable, and a good idea. My new home, a condo, is not well insulated, with old windows, a leaky door, no basement and an upstairs neighbor that kept me cool with his air conditioning through the the hottest days of late summer. I think I will try your test and see if I am returning the favor with my furnace. I think using the fan feels more comfortable when I'm sitting in my living room, but you've given me a good way to test it with science!

    1 reply

    Thank you for reviewing and commenting. I am pleased that you may find some tangible
    benefit from my experiment. If you do
    find some trapped ceiling heat and you use a ceiling fan to blow the heat down, I would be interested to know how much heat is being created by the fan motor its self and how
    much is being removed from the ceiling.

    I guess I am a little confused about your test. What exactly did you manipulate to cause the heat to move downwards? It sounds as if you just performed an analysis and did not have a clear independent and dependent variable. Just wondering if I'm misunderstanding something.

    1 reply

    I am sorry for any confusion. You are right I performed an analysis. I stopped the experiment because of the
    results of the independent variables. I
    concluded, based upon the average Ceiling temperature being the same as the
    average Mid temperature, that I could not raise the ambient temperature. There was no trapped heat at the Ceiling to
    move down and warm up the Mid area. I could not change the Mid temperature by
    moving the Ceiling heat down. My
    hypothesis was to raise the overall room temperature by moving the Ceiling heat
    down. They were both the same; there
    was nothing to gain by continuing to experiment. Had the Ceiling temperature been 10 degrees deferent then the Mid
    section, I would have then moved the excess heat from the Ceiling down to the
    Mid or Floor and measure the gain at the Mid section. You understood clearly, I did not explain what I did well enough.

    Thank you for reviewing and commenting.