I Made this heat-crabber collector using Some 1/2" fiber board insulation,3/8" plywood and 1/8" acrilic panels. It is 8'x26" to fit my window. I had these materials and did not buy any. I used alum. screen frame molding to hold the acrilic panels placing the panel in the spline grooves.
On a 40 degree day I get 140 degree heat coming out. It raises the heat in that room by 10 degrees. Made the mistake of painting the collector with oil base paint. Took about a week for the odor to subside. Best to let it cure before installing.

Mike,
Not sure what you mean by counter flow. An good active collector has a one inch airflow chamber in a straight pass 16 to 20 feet long in order for the air to scrub the collector plate to pick up heat.But considering it is hard to build this type of collector you could make the air chamber deeper and use flow disrupters in the collector.
An output for the heated air at the bottom of the collector does work well but todays ceiling fans use no more power than a light bulb and would distribute the warmer air back to the floor.One type of active collector I build has the inlet/outlet on the same end of the collector,top or bottom which ever way you install it.It also helps prevent backflow at night.Like I say go to www.builditsolar.com the best DIY alternate engery site there is in my opinion.It's a wealth of info for anyone starting an alternate energy project.
Greg

Has anyone tried to build an active system with the fan running counter flow. I believe this would give the heated air longer residence time and possibly eliminate the need for baffles. It would also have the air exiting low which is more efficient for heating.

God bless,
Mike

Kirk,
About your 4x8 collector the printing press or litho plates as they are called work well for an absorber.But if you want to power your collector with a fan it will become an active collector.I built an 18sq.ft. active collector that is on builditsolar.com,"search for"(Greg's Solar Air Collector) for around $40 and was pleased with the results.I now build some active collectors called back=pass collectors that work much better because the heated air isn't in contact with the glazing making them more efficient
I like aluminum absorbers because they heat up quickly.One note,if you decide to build an active back-pass collector I recommend that you do not use lexan,use tempered glass.As for the aluminum,sometimes you can get the litho plates from your local news paper for free or just use house trim coil or sheet aluminum if you can afford it.Put baffles in your collector to make the air travel 16'to 20'before exiting the collector.
Greg gwest77@netscape.com

To all the above,about the insulation board.Use only foil faced polyiso.because it can withstand the heat.Johns Manville,R-Matte,Dow are all different brand names you can get. Lexan does make a good glazing if it doesn't become to hot, but low iron float glass is a better choice I think unless you have the bucks to shell out for solar glass. Kirk,why are you putting your collector on the southwest wall and not the south unless it's because of obstacles that will shade the unit.The rule of thumb for air flow through a collector changes somewhat with your altitude above sea level.At sea level it's 2-2.5cfm per sq ft of collector area and goes up from there say at 2500ft.above sea level it would be 2.5-3cfm,at 5000ft it is 3-3.5cfm and 7500ft above sea level it would be 3.5-4cfm.Now that said when you buy a fan the rated cfm's is not what will come out of the collector because of what they call static pressure(water gauge)My advice is check out builditsolar.com
for almost all your questions :-) Greg

I bought these plans back around 1980 and built the Heat Grabber. It worked great but my wife didn't like the appearance of the thing hanging on our dining room window so I eventually trashed it. We have since moved and our south facing windows just face a wooded area and I would love to build some more. Unfortunately I lent the plans to my brother in law who later divorced my sister so I no longer have them. It seems to me that many of the foam insulating panels available at Lowes or Home Depot would work just fine. Since I no longer have the plans I don't remember the thickness they should be or what the recommended R value is. I remember buying some sort of non glass glazing material. For the life of me I can't remember what the heat absorbing material was. I sure wish I had those plans now. It is a very worthwhile project.
Jim (jhenry@airpower.com)

My father sells, or reps rather, roofing supplies. There is always an alternative to dow. Like a previous poster stated, go to your local lumber yard or roofing/ building material supplier and ask for polyiso. I don't know if using plain old hard styrofoam is going to cut it. It will do the job I guess but insulation is specially formulated and has come a long way from plain old packing styrofoam.
Look for a local brand of insulation if you can! Buy local! There seems to be many companies that produce iso. Good Luck!

I am planning to build a 4 x 8 passive solar air heater to attach to a south southwest wall of my house and wanted to make it fan assisted and was wondering what the rule of thumb was for cubic feet per minute was to square footage of collector. Also what the best absorber material is I have three window “sun grabbers” currently installed and had used printing press plates painted black with regular paint. I was also wondering if lexan is a good glazing material.
thanks

When all else fails, use the solid styrofoam (like is used in packaging so many things nowadays). That way you can be recycling while you are cutting your energy bills. A Double Win!

You can also make your own out emergency space blankets and styrofoam. It's cheaper, sustainable and just as efficient.

Google "polyiso".

Thermax is a brand name. There are a bunch of suppliers. Call your local lumber yard and ask if they have polyiso in stock.

I bought my Thermax at Home Depot for about $15 a sheet for the one inch thick 4X8 sheet.
I had gotten a 22X62 thermo pane window that had been removed in a remodel and had a window that was 25 inches wide so the dimensions worked out well for me. I started to build the solar heat box out of the Thermax alone, but had gotten some scrap aluminum used for trim on houses so I wrapped my box with that.
I'm using the box to help heat a room that is part of my unheated garage. I use a small electric heater at night and wanted something to help warm it during the day. I keep plants alive through winter in there. I bought a La Crosse wireless thermometer with a secondary probe to see if this box was helping to warm the room. This is December and the daytime temperatures have been in the upper 20's. The room interior temperature is around 50 F and the air coming out of my window solar box is right around 70 F at noon. At 11AM and 1PM there is about a 10 degree increase.
The cost of the project was about $50

Is there an alternative to a DOW product? I try to avoid anything bearing their logo.