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Old 09-06-11, 12:58 PM   #1
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Default Indoor black sheet heating?

This seems super simple and I find it hard for it to not help a little bit and couldn't find anyone trying this, probably because it is fairly obvious but I'll post anyway because I'd like it to work the best that something like this possibly can.

I don't have much southern glass on my house, which is great to keep the A/C bill down in the summer but for the winter I'm not getting much heat through the windows. The design of my house doesn't really lend itself to well to change this either unless I wanted to tear a window off of the east side of my house to put it on the south side, I can't really just add a southern window and call it good and that has high cost, planning, etc too.

What I want to do is to maximize the heat I get out of these 1.5 foot(glass width) octagon shaped windows in the master bedroom, which is the most important room to heat for me. What I'd like to do is to hang something black from the ceiling in front of the window but how do I maximize the heat from something black?

I was thinking of getting a thick wool black fabric that is big enough to capture the sun as it sweeps across the sky, but also place it so its not too far away to where I'd need something that spans the room.

Is fabric the best for this? If not, what would be better?
Do I want something thick or thin?
Would adding a small low powered fan blowing on the material help get me more heat out? Is there a maximum temperature where it will settle at?

I don't think I'll get a ton of heat from something like this and I'm considering making a black drape for the west facing windows of the house to catch the evening sun before night comes with a gap wide enough to allow for it to clear the air-sealing window plastic and allow for natural convection to hopefully carry some of that heat into the room. What do you guys think? Worst case, its a failed trial of buying and cutting up a cheap wool blanket for these octagon windows and black bedsheets for the other western windows but I don't see how this would fail, might just be a long payback period but I don't think so.

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Old 09-06-11, 05:46 PM   #2
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I don't know if any fabric or textile would do much more than warm up, feel warm to the touch, most would act as a "self insulator". If you are trying to harvest heat from the sunlight you'd be better to have something thin and dense, such as metal or plastic, so that it would convert the sunlight to heat and shed the heat to the air quickly. Perhaps a vertical or horizontal blind, preferably with dark coloured metal fins, or, as size permits, a couple of those litlle 1w solar panels c/w a 2 or 3" 12vdc mini fan. Realistically though, your small window won't give you a lot of heat, but you might have fun with the solar panels!

Last edited by herlichka; 09-06-11 at 05:49 PM.. Reason: grammar
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Old 09-06-11, 07:53 PM   #3
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Good to know, I can easily track down a thin sheet of aluminum and spray paint it black as I wouldn't need to use a fan in that case as it would likely easily flow off of the metal considering heat sinks are made of aluminum. Fabric though, if the surface is warm that surface will radiate heat. I've felt the heat rising off of a pair of blue jeans sitting on the carpet while the carpet right next to it in the sunlight was cold.

I'd have to dismiss the solar idea in this application because the cost of small cells in the quantity I'd need would be more effort and expense than its worth, I could easily use a switching power supply for a small load like that. Fun with solar panels is great but I've had my fun with small panels and if I do anything with them in the future it will be an array of around 4kw which would produce well beyond my yearly electricity use.

I don't need much heat gain to make much of a difference as last winter's largest gas bill was 86 therms or $70 including service and city fees($10.50). I'm just looking to augment heat gain wherever I can. I've mostly finished air sealing and haven't added on to the attic insulation yet as the only air sealing left to do is the attic and as it is getting R75 cellulose up there. Once I do that I'm curious where the heating bill will be but I'm also curious what a spray foamed or well sealed new construction using 2x6 framing with blown-in cellulose and properly designed southern glazing looks like for gas usage in the winter.
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Old 09-06-11, 09:03 PM   #4
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Placing something inside your windows to capture extra heat will have no effect. The amount of energy entering the room via a window is fixed, that energy is absorbed by all areas in the room subject to the light falling on it. Placing anything behind the window does not magically increase the amount of energy from the sun entering your room.

If you want to keep the heat in the room then double glazing the window will have the most benefit.

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Old 09-06-11, 09:10 PM   #5
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Why don't you put a HW solar panel on the side of the house?

I'm not an HVAC technician. In fact, I'm barely even a hacker...
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Old 09-06-11, 11:29 PM   #6
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Solar Mike, Thanks. I figured that when white things in my room never got warm that it was heat that wasn't absorbed, does that just mean that this was light reflected to another spot in the room and that got light got other things darker instead?

With that out of the way, I suppose we can have some topic drift in the thread.

AC_Hacker, the design of my house would make a hot water(or air) panel mounted on the side of the house look bad as there is no shrubbery or trees to hide it and in order to try and hide it I would have to have trees on my neighbors lot as the line of sight of the curving road I live on draws peoples eyes directly to the south side of my house. I'm also a bit nervous about making penetrations in the side of my house and being sure everything is well sealed. Also I'm not sure how much benefit I would get from HW or HA in a Minnesota December and January when I really need it but we only have 3.5 hours of sun on a clear day limiting what heat can actually be created. Then I've got to figure out to efficiently distribute the heat of hot water into the air while not creating leaks and causing water damage. Water damage and condensation are major homeownership fears of mine. I think I might have better benefit from solar PV if I went the solar route as I think I'd get the most benefit from that. As far as my basement hot water tank, my methane gas bill was for 4 therms/CCF the past two months so there really is very little standby loss there and I manage hot water usage well too so I'd probably overkill the tank in the summer as I think 400,000BTU or so(actually less as my stove/oven runs on the methane gas too) would be fairly easy to produce over the period of a month. For awhile I wished I could use a timer on my water heater but it seems there is no need for it when you've got a tank that supposedly has R20 insulation built-in. Either that or poking the gas meter outside with a pointy stick has been working wonders. ...on a serious note after I moved into this place someone in a gas company truck come out at the end of February and looked at the meter, probably a red flag to have a yearly meter spin of just over 300 ccf a year when the previous owners were in the high 150's last January, huh? Properly used spray foam, ductwork that handles the pressure, efficient furnace cycling protocol, and not setting the thermostat to Tahiti mode apparently does wonders.

While we're on the topic of heating, I've considered going the heat pump route to reduce the energy usage of my old inefficient air conditioner and hopefully squeezing more time out of a 28 year old 76% efficient furnace but when I do the math it seems that in my climate even with some of the most efficient equipment I don't stand to benefit on the cost and if I replace equipment for something like a cracked heat exchanger than I'd be getting an efficient A/C anyway and central heat pumps aren't efficient enough to make sense here with our super cheap methane gas, especially if I junk the 76% efficient furnace for a 95%, I've been told by a bunch of HVAC guys to skip the 95% and go with a new 80% because it'll never pay off. I don't share their point of view though, it might take a long time but there is lots of savings to be had for piping my outside air into the combustion chamber rather than sucking it through as negative pressure infiltration.

Last edited by MN Renovator; 09-06-11 at 11:37 PM..
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