Air Sprinkler

Summer Cooling With This DIY Bed Fan Hack

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We live in NorCal, in an area with a very temperate climate. It rarely gets too cold, and it rarely gets too hot. While we have a furnace for keeping warm when it’s cold, we don’t have A/C for when it gets hot, so we depend upon fans. But when we go to bed, even with fans on in the room, and even with the lightest sheets, it can still get uncomfortable. So, I went searching for a solution.

Bed Fan
Image via Amazon

What I found was this very slick $400 solution with an app-controllable fan that could deliver either room-temperature, or warmed, air under your sheets for extra comfort. It would certainly do the job, but at that price, it was a bit expensive, we didn’t need the heat function, and the app-control was just gilding the lily. However, looking at the whole setup from my engineer’s perspective, I thought I could come up with something myself that would do the job and be a bit more economical.

Realistically, it wasn’t hard. Again, I headed to Amazon, and found the key component:

Duct Fan

This is the Apollo Horticulture 4″ 190cfm Inline Duct Fan, and costs $60. It’s specifically made for ventilation of greenhouse setups, but could be used for all sorts of similar needs where you need to move air via ductwork. It’s reasonably quiet, and moves a decent amount of air volume (there are higher-power units available, but this one has worked well for us).

Duct Fan and Hose

I started with just this and an 8′ length of flexible hose ($9), and pumped floor-level air under the sheets at the foot of our bed. It worked pretty well, but the end of the hose would move during the night, and make the overall cooling a little inconsistent. So, I needed to device a way to spread the cooling air out, and keep it in place.

Air Sprinkler

My solution: a 5′ length of 4″ Schedule 40 PVC pipe (which I picked up at my local Ace Hardware, costing about $15). I put a cap on one end, duct taped the open end of the flexible hose to the other, and then drilled holes down the length of the pipe to create what I’m calling an “air sprinkler.” There was even a bit of engineering design that went into the size and number of the holes. I realize, to be able to deliver the same flow of air that the fan was generating, I needed the total cross-sectional area of the holes to equal that of the outlet of the fan (4″ in diameter, or a 2″ radius).

It was a pretty easy calculation. Since area = πr2, the area of the fan output was π x (2)2, or 4π, which is about 12.6 square inches. I settled on a 3/8″ drill bit, which creates a hole with the cross-sectional area of π(3/8)2, or about 0.44 square inches. With this drill bit, I could make 12.6/0.44 = about 28 holes and maintain pretty good efficiency. I then just laid out an even pattern across one side of the pipe, imagining it facing towards our feet under the covers, and evenly spraying our feet and filling the lower bed area with cooling air.

It works. It works really, really well. We’ve already had a couple very warm nights this month, and where we’d usually end up tossing and turning even with floor fans on in the room, each of these nights has been comfortable. Even though the air under the sheets is just room temperature, it does a great job of keeping thing cool and comfortable. Total price: about $85.

I’m still working on some fine details—like putting some kind of base on the pipe so it won’t roll during the night, but that’s been a minimal problem. And yes, I know it’s a little goofy to have a big plastic pipe under our sheets while we’re sleeping, but the key point is that we’re sleeping – comfortably – and that’s totally worth it.

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23 thoughts on “Summer Cooling With This DIY Bed Fan Hack

  1. I just made a similar contraption but I used this Duct Fan: https://www.amazon.com/gp/aw/d/B06ZXWN3BG
    Cost only slightly more. $80 at the time I bought it. Comes with a temperature probe (which is tucked under the mattress protector at our feet) and control unit that can power and control two fans should we decide we need a second. As the bed gets warmer the fan blows faster! Still trying to work out the best way to get air into the bed. I like your idea of drilled pvc. I have a length of lay-flat tube that I might try something similar with.

    1. David – that looks great. I don’t think it was available when I built mine, but if I do an update, I’ll totally pick one of those up!

    2. Thanks for posting this! I am considering building my own. Still trying to sort out how to cleanly get it from below the bed to above and to be able to keep it in place securely and discretely. One path I was looking at was using pvc/vinyl gutter pieces. I believe I may have just enough room between my mattress and baseboard to fit some downpipe. Still need to figure out an air filter for the pump as well, we have pets, and I don’t want to shoot pet hair balls into the bed. lol

      One example of converting from 4″ round to 2″x3″ downspout format:
      https://www.amazon.com/Amerimax-Home-Products-Flex-Drain-53227/dp/B008BGZ9CY/

      Then extending up with
      https://www.homedepot.com/p/Amerimax-Home-Products-White-Flex-Elbow-37084/

      Then could potentially leave a narrow nozzle or do something similar to
      https://www.homedepot.com/p/43-in-Low-Profile-Downspout-Extension-Kit-4601/303522071

      1. All very good ideas! I just improvised with the flex hose, so it would be easy to move it around, but after using for a while, I realized I needed to trim it to length, or it would expand just from the internal pressure from the fan.

        As for the filter, that’s a good thought – easiest would be to tape some fabric over the intake. You just have to balance how well it filters with the addition load it puts on the fan trying to suck air in. GOOD LUCK!

  2. I am trying to find the person that created a bed fan here on kickstarter. It sits on the floor with an extension that goes up and curve toward the bed. I am angry. It took over a year and even brand new didn’t work well. Now it doesn’t work at all. Frustrated customer.

  3. Great idea & thanks for sharing. I’m in the process of putting one together for our bed. Quick note though: In ensuring the total area of the holes drilled in the pvc pipe matches the area coming out of the fan, I think your calculation was a little off. If using a 3/8″ drill bit, 3/8″ is the DIAMETER, not the radius of the drill hole. You may need some additional holes to keep pressure constant.

  4. My wife is always warmer than me so this is a great idea! We are also paranoid about toxins, we have a 100% natural latex mattress and organic cotton sheets so I was not about to lay PVC in the bed between us.
    On Amazon I found a 10-foot length of silicone hose with a 3/4″ inner diameter and 1″ outer diameter (about $30) and a collapsible silicone funnel that went from 4″ to 1/2″ (about $5).
    Using the AC Infinity CLOUDLINE T4 inline fan recommended in the comments above (now about $80 w/o thermostat) I used the enclosed metal hose clamp to fasten the funnel to the fan. I cut off a bit of the end of the funnel, just enough to squeeze through a 3/4″ copper coupler (Home Depot, $1) to attach an 18″ section of the silicone hose, this got it to rest on the floor with no kinks. I thought the hose would kink if I just bent it up to mattress height at the foot of the bed so I attached a 90-degree copper elbow (Home Depot $2.50) and ran 7 feet of hose to the head of the bed. I used a utility knife to cut small holes at even intervals on one side only (to cool her and not me) and put a rubber stopper (Home Depot $1.50) in the end.
    So if you are crazy like us but still want a between-the-sheets fan this is a good no PVC or vinyl solution.

  5. I splurged and ordered the OEM air nozzle directly from Bedjet. It was $19 shipped.

    Be aware, the hose connection is 3” diameter.

  6. Hi there. I absolutely love this idea and don’t think it would be too hard to make at all. My only question is how often do you kick the pvc pipe at the end of the bed? Both my boyfriend and I are very tall and reach all the way to the end of our bed. I am concerned we will catch a toe in one of the holes.

  7. We built this a few weeks ago and love it. It took some trial and error making it work with our sleep style. We both kick and move and pull blankets in our sleep. We ended up taking our flat sheet and sewing on a few ties then tying it to the foot of our bed over the fan. Then we used some belts to hold the PVC in place by attaching it to the bed frame. Works like a charm. The fan is no louder than the window fan that we have going.

    This is going to be an absolute life saver when the wildfires start up and we can’t open the windows from the smoke. Seriously, my only complaint is that I wake up too cold sometimes!

    1. I don’t know that you’d be able to get the same volume of airflow. Pool noodles usually only have about a 1″ open core, compared to the 4″ PVC suggested in the project. However, you might be able to get some non-rigid pipe, like dryer vent pipe, and make it work.

  8. What is the noise level on the AC Infinity CLOUDLINE S4, Quiet 4” Inline Duct Fan next to the bed?

    This question if for those that have installed the fan with the manual control and the temperature control units. I talked to the manufacture and they indicated the advertised db level of < 28 db is when it is installed in the attic in the duct and the db level is measured at the ceiling air outlet and not next to the fan.

    Also would like to know the person that installed the temperature control module – how does it working for your installation?

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