12 mo. ago • 100%

Using "waste" heat to heat your home in the winter...my journey

I have my office and rack in the basement where I work out of during the week. In the early spring and late fall when there isn't much cooling it would get rather warm to be comfortable (80F-82F).

A few weeks ago I realized that I have a cold air return duct in the ceiling so I cut an 8"x10" hole in it and left the furnace fan on 24/7 hoping that would help...it didn't really.

Last week I decided to hang an ~8" fan 3" below the hole I cut into the cold air return to see what would happen if I forced air into the duct...it didn't do much.

Last Thursday I remembered something from my volunteer firefighter days about how to set up a fan to ventilate a room through a window/door and how it was important to have the wind cover the entire opening. This led me to put a 12" fan in place of the 8" fan at 9PM.

Fast forward about an hour and my office was now 76F. The next morning it was 72F and it has stayed at 72F-73F ever since then.

The side benefit is that I'm able to provide a bunch of supplemental heat to the upstairs meaning that rather than my heat pump running 16hr+ per day with the electric strips kicking on periodically overnight during the <15F weather we've been having the heat pump has been running for 8hrs per day and the electric backup strips haven't needed to kick on at all.

I'm curious how it works for cooling next summer when I won't be able to run the furnace fan 24/7 since that'd just dump humidity back into the house so we'll see how that goes.

I'm still pretty happy with the results at the moment.

31 comments

The fan suction trick does wonders. Learned it as a teen trying to uh... Ventilate some smoke from my bedroom lol

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I've been doing something similar but simpler the past few years. I just have every pc in the house setup as a tdarr node, and at night they all work full blast. Even my laptop is setup in a room to help keep the warmth going.

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I'm not sure what you're saying. You have a forced air system with a cold air return? What did you cut a hole into then?

Running the circulation fan constantly usually doesn't help. If you have any ducting buried underground or in an attic (unconditioned), you're just going to waste electricity using the fan, and dumping heat through the ducting into the attic or wherever.

Most systems have 3 fan settings 1) auto - run fan when heat or cooling are being called for 2) on - run constantly which is a waste 3) circulate - run fan for 2 minutes or so, every 10 minutes or so. Option 3 is what you want. But realistically "auto" is probably best unless you're generating a few hundred watts or more in that one room.

A box fan in an open door will probably serve you better. Because it's not pushing conditioned air through unconditioned space. It's all staying inside the rooms and hallways.

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My equipment lives in my family room. I’m in SC and run three fully populated Dell r720XD’s 24/7. It keeps the house warm in winter, but heats it up more during the summer (it sucks!). I haven’t found a solution to exhausting the heat without creating a negative pressure in the house causing outside heat to be pulled in, unfortunately.

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- Enclose it, route outside air in and back out?
  
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  Humidity in the South hits 100% way too often, unfortunately. I’d imagine that would not be great for them.
  
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I heat my small home office room with waste heat from all the stuff in it. Only drawback is that I have to cool it actively on hot summer days or stuff will shut off.

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In my old house we exhausted the heat out a window in the summer with a Dayton fan and 6" ducting , in the winter we circulated it to supplement a pellet stove.

Now in my own house servers are in basement along with my hybrid hot water heater.

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If you did nothing, the waste heat would heat the basement, rise up into and through the floor, and heat your house anyway.

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- Not in my experience over the last couple of winters. The office just stays at 80F or more while the rest of the basement is 70F even with a fan blowing from the office out into the main room in the basement.
  
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  Heat moves along its gradient.
  
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Linus is that you?

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Pics or it didn't happen

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Be aware that running the furnace fan on all the time in the summer (anytime you run the AC) can cause high humidity in your house. The condensation on the coils evaporates right back into the circulated air, instead of dripping and drying before the next cooling cycle. I thought running the fan would circulate air better and keep my computers cooler, but the high humidity made it feel muggy even at lower temps.

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Have you considered water cooling? Then get in irradiatiors?

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Where was that heat going before you added the fan? It had to go somewhere…

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- Some of it would leave, however, most of it stayed in the office which it’s why it was 80F+ in there.
  
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If your PC/server consumes 200W, it emits the heat of a 200W heater (which is very low btw).

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- I have a constant 1000W load which is ~3400 BTU.
  
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- https://www.reddit.com/r/askscience/s/Hf09vxZnQi
  
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- Its not 1:1 obviously. Most energy turns in to heat, but also energy gets ‘lost’ in spinning a disk or fan for instance.
  
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  Energy spent in spinning also ends up turning into heat, due to friction.
  
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- Lol 200W I could only wish.
  
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