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Question
Hi,
I've been trying to conserve heat.
I've been doing some experiments on whether or not to place a filter over my heat register.
I know of course, putting anything over the heat register will cause it to work longer to heat up a room.
But through oberservation and data collecting.
It seems that putting a filter over the heat register will help the room retain heat longer versus without one.
For example: Without Filter- It takes 20 mins to heat up room, but it will only retain heat for 8 mins before heater goes on again.
With Filter - It takes 25 min to heat up room, but it will retain heat for 28 mins before heater goes back on.

The difference is only 5 mins apart.
My question is, why is it with a Filter, heat will retain longer versus without one? This is what confuses me
Hope you can help.

Answer
Well, a few things are going on there.  First, you are adding a thermal mass to the system by adding a thing to heat up.  That will mean that the heat stored up will both take longer to bleed out into the room, and more of a quantity is stored.  Proof of that you already had, it obviously took longer to heat the room up.  Second, the thermostat.  If it is inside your filter, it will take longer to cool down and re-activate the heater...but since it didn't shut off right away, I expect that it's outside?  In that case, you've added so much heat to the room that it just took that long to cool off.  If it goes on and off on a regular cycle like that, then that's what's happening.  Overall, I suspect that the temperature in the room dips a bit below what it goes down to with no filter.  You'll get better results by turning your thermostat down and removing the filter, overall.  If you have a thermometer inside the room, you should check and see what it goes up and down to.

Update:  What I meant to get across there was that I don't think this is a magic method for saving energy.  You're probably just living with it getting colder a bit, even if it lowers your electric bill.

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Dr. Stephen O. Nelson

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I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

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I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

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Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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