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Posts: 2,123
Reply with quote  #1 

Happy New Year everyone! I hope you had a great holiday season. We have gained almost 6 minutes of daylight since the winter solstice. But the sun is still quite low in the sky, which means the sun has to pass through more of our atmosphere(and perhaps, trees) before reaching our collectors. 

But over the weekend, as we celebrated the new year, and we also experienced the bitter, bitter cold. With highs well below 0˚F during the day, and even colder at night. Windchills reached -40˚F at times. It’s times like this I’ll admit I almost look forward to, as the coldest days are usually the sunniest. 

Over the last few mornings, with the air temp -10˚F or colder, I watched as the sun reached my collector and very slowly burned off the layer of frost on the glazing surface. Steam slowly rising from the collector near the top and working its way down. Even when the glazing was clear, the interior of the box was still far too cold to activate the snap switch. But once warmed up the collector began producing almost as much heat as if it were 40˚F warmer outside. Very satisfying, to say the least.

What kind of solar heater performance should we expect and have you experienced when the outdoor temps are so bitter cold? Does the collector type, size, install location matter? And if so, to what degree? 


Greg in MN


Posts: 119
Reply with quote  #2 

I forget what part of MN are you in, I am in Maple Lake, MN. My Christmas present was 3 day's of good sun ;-)

Remove window and storm door screens, wash windows, hang black felt in between door's, set mirror's and PV's to run fans. And pray for a cloudless sky ;-) Had good sun this am till about noon, then clouded over :-( Was getting 136 out for a bit ;-) With the mirrors I have seen 145f regularly, so could use bigger fans. Snow on the mirrors will drop collector temp 15f. No mirror max is about 120f.

This was taken about a month ago. Plenty of room for more collectors, just need more time ;-(
Wood peckers 007small.jpg 
Top of door with hole, fan, back draft damper and magnetic vent cover for night and cloudy days. The black cord is the outdoor probe (from I/O thermometer) that is mounted on the other side by the fan.
solar door heater 005 small.jpg

Bottom, not visible is the back draft damper on the other side.
solar door heater 004 small.jpg 
 Curtain rod and felt at top. The felt warped some in a stagnation event :-( but still Works ;-)
solar door heater 006 small.jpg

Curtain rod and felt at bottom.  The string is in an X to hold the warped felt away from the door.
solar door heater 007 small.jpg 
Small 36" x 80", and crude but with the solar gain from the windows, this is enough to keep the LP furnace from running during a sunny day. Often from 9:30 am to 4:30 pm or longer depending on outdoor temps.


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Posts: 469
Reply with quote  #3 
We've been in the deep freeze also. Down to -15F a few days back. We are lucky to get out of the single digits. May finally get to 20 coming up Sunday.
On full sunny days we get plenty of heat from the solar collector. Been getting a mix of sun, clouds and hazy days. 
On the hazy days we still get some heat but not like those sunny days.
This has been the coldest stretch in a few years now.  Praying for more sunny days...

Bert K.


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Reply with quote  #4 

I live not too far from you due north of downtown Minneapolis. I'm as far north of downtown as you can get. I'm up in Maple Grove a few times per month and even stop up in Rogers to shop a few time per year. So if you ever feel like getting together for some "solar shop talk", send me a note. 

I only have one window that faces south and I do remove the full screen over winter. The south stoop has a rather large cover over it so only the lower portion of the door receives sunlight. I admit, I do open the interior door on a sunny day when I'm home and only use the full-length glass storm door. Yes, it likely a heat loss, but having such a clear blast of sunlight into the dark entry is worth it!

I must say, it's pretty ballsy to cut holes in the door like you did, but...I like it!

Greg in Minneapolis(SKOL VIKES!)

Posts: 119
Reply with quote  #5 

I must say, it's pretty ballsy to cut holes in the door like you did

Why do you say that? ;-) 

Actually we used the collector for 2 or 3 years without the fans or holes. By watching the thermometer, when it showed 95f or higher we opened the door a bit. If I felt cold air at the bottom of the door it was open too far, as the temp got higher I could open the gap a little. It was a balancing act to get hot air out and no cold air. I hated to go to town on a sunny day because I didn't want to leave the door unlocked. That is how it stagnated, I went to town for an hour, with the mirrors the felt was at 295f. Stinking and left some of the fuzzy bits melted to the door. The door enters into the living room so we almost never use it.

I tapped on the door with a hammer to get an idea where the edge of the cross braces were, then drilled a small hole and probed with a stiff wire to get it right. Then drilled the hole with a 3.75 hole saw just missing the brace. Then trimmed the inside square as you see so the fans would slide in with a friction fit. The outer skin has a round hole that holds the fan in place. 

For summer I take the felt down and roll it up for storage. And place some magnetic vent covers over the holes to hide them.

In 2005 I had several arguments on the house orientation during the permitting process. They insisted the house should be turned 90 degrees so the length would be parallel to the road. Obviously I won the arguments ;-)


Posts: 139
Reply with quote  #6 

"They insisted the house should be turned 90 degrees so the length would be parallel to the road. Obviously I won the arguments "Well done! IMHO all new builds should be obliged by building regs to have their roof pitches (not necessarily the house front) oriented towards the south where practical, making them ready for solar PV or HW heaters.  Would also make for some interesting profiles and get builders and architects thinking out of the box.

Up here in BC Canada new builds must be pre-wired (or have conduit in place to pull cable through), for EV charging in the garage, it would be great to also have conduit to the roof as well.  No mention of roof orientation yet though. ;-(

Posts: 1
Reply with quote  #7 

Gordy, your front door solar heater is such a great idea. It struck me that this could be a really easy way of making stand alone solar collectors using a second hand insulated metal door and a storm door. I'm assuming that the glass in the storm doors isn't low-E, so is pretty much tailor made. I would imagine that these components should be readily available at Re-store type places, or swap sites for modest costs.

cheers, Andrew

PS. First post here. I've been reading about lots of projects for the past few days. Pulling together ideas for something quick and easy to make using components I have around here. I want to see if I can get some warmth into our currently unheated basement.

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