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I know I have been awfully quiet lately; nowhere near the level of activity that I once managed. But I don't want to give the members of CleanMPG the impression that energy efficiency has fallen off my radar. In the absence of poor gas mileage I have been putting most of my energy (and somewhat limited free time) into winterizing the house that my wife and I bought last spring. Overall the house is fairly tight for being ~30 years old, and the decrepit natural gas furnace has been replaced with a new 95% efficiency model. But like an efficient car, it would kill me to invest the bucks in hardware and then "drive the H$!! out of it." Know what I mean? So I couldn't bear to start the heating without addressing one huge, gaping hole: the windows.

In their day these were “good” wood-frame Anderson crank-out windows. By today's standard they are quite poor. Warping has introduced at least some air leakage, and if there's a second pane of glass in there I can't see it. (My dad insists that they are double-pane but I don't believe it.) Evidence of their inefficiency is the tremendous amount of condensation on the inside on a cool fall morning, which tells me that the surface of the glass is quite a bit below interior air temperatures. That translates to some nasty convective heat loss through every one, and I count 23 of the blasted things.

Replacements are expensive, and frankly I'm in no position to pick up that kind of bill right now. The plastic film is a good and much cheaper alternative, but I don't like having to throw the film away in the spring and install again next year. It can also be unsightly. So I have chosen a third path: interior storm windows. You can buy custom storm windows if you want, but those could run upwards of $100 each. Fortunately they are easy to build if you have table saw, a couple hundred bucks, and some time worth investing.


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Just because I haven't cut off a limb [yet] with my power tools doesn't mean you won't. I also cant guarantee the results if you decide to follow any of these instructions. (I also can't guarantee that your results won't put mine to shame, but that's not what disclaimers are for.) Attempt this project at your own risk. (And don't forget to count your fingers and eyes.)
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The purpose of an interior storm window is to put a barrier between your hard-earned warm air and the leaky old windows that you and I can't afford to replace. They work in two ways. #1 is to stop air infiltration, which is like leaving the window cracked with cold winter air pouring into your home. #2 is to mitigate convective heat losses. Air naturally circulates over surfaces that are colder than the ambient temperature, and as it does so it dumps heat into that surface. Putting something between the warm inside air and the cold window glass reduces heat flow out of your home. In this case I am using the interior storm window to stop inside air from coming in direct contact with cold glass. It can't stop convection completely, but it does add substantial resistance to heat's path toward inevitable escape.

Construction of my own interior storm windows is based on guides I have found all over the internet. Each storm window starts with a simple wood frame which has been sized to fit in place of the screen that are normally fitted to these windows. The raw material is "select pine" 1x2s that I have ripped down to about 3/4” x 3/8”. I cut tongues into the long sides and grooves into the short sides, and joined them with glue. (I don't have a dado blade, but I got by with multiple passes over the normal blade. Cut the grooves first, then gradually adjust the blades so that the tongues fit tightly.) The cross-bar will be held in by compression, anyway, so I just roughed them up, glued, and clamped in place to set. A couple pics:

http://www.cleanmpg.com/photos/data/500/Corner_Joint.JPG

http://www.cleanmpg.com/photos/data/500/Unfinished_Frame.JPG

Once sanded and stained, I cut a single piece of that heat-shrink window film to wrap around both sides. A one-sided installation should give a substantial benefit, but I found through experimentation that the second layer gave a measurable increase in surface temperature. With outside temps of about 40F and an inside temp of 68F, un-treated windows read about 58F with the IR thermometer. (Use a piece of masking tape on the glass/film so that it has something to read). The one-sided storms were reading between 63 and 64F, and the two-layer windows (which trap an extra layer of air) were reading about 65F. I haven't bothered to calculate the corresponding heat flux but it seems worth it for an extra few cents in film.

http://www.cleanmpg.com/photos/data/500/Finished_Storm_Window.JPG

For now I'm fitting the storms using 3/16” weather stripping and some fine wire brads. (I'm sure there's a better way but this works.)

Overall I'm very happy with the end result. More importantly, my wife is happy! Even with two layers the film is unobtrusive. They might even be an improvement given that there were ugly screens in the way before. Total cost is running between $6 and $8 per window using pine for the frames. Hardwoods might be nicer and/or stronger, but would be more expensive.

Thoughts on improvement:
-Moisture between the layers of film might become a problem. If so, some desiccant might be the way to go.
-Frames for my tallest windows (60”) bow from the film shrinkage more than I expected. I would recommend two cross-bars rather than just the one, or make the frames from stock wider than 3/4” to add stiffness.
-Don't forget that heat still radiates through anything transparent! Curtains are still important, especially on a cold night.

The take away:
Saving energy at home is just as important as saving it on your commute. Windows are usually a big ticket item as well as a big energy drain, but it's important to remember that simple & cheap steps can go a long way. This project will come in well under $200 in my case and the gains are significant.

Moving this post into the general forums...

Very impressive, Tim!! :thumbs_up:

I was going to mention that you should add the film to both sides of the frame.You did not give me the chance! Good thinking and backing up the results. H

Great initiative Tim. The results look very impressive. Maybe I'll give it a try for some of my larger windows, though I already have dual panes. Windows are a terrible heat sink.

Home heating efficiency is very important. I actually use more energy in the form of natural gas than gasoline.

I would encourage everybody to do a DIY home energy audit (http://www.energysavers.gov/your_home/energy_audits/index.cfm/mytopic=11170). It's easy to do, and the benefits are large: a greener, more comfortable house, and lower utility bills. A tube of caulk might pay for itself in energy savings in a week.

Another cheap test is a toilet leakage test for wasted fresh water. Put a few teaspoons of food dye into your toilet tanks and see if you get any color in the bowl after an hour. Wasted water can be expensive also! Good ideas all.

Cool-aid works for checking toilet for leaks as well. I do this on a regular basis. Don't want to waste water. H

We have a cat with claws.

I bought a few insulated curtains from the store this past summer that claim to save up to 25% on home heating costs. It drops to 31F here at night and so far I haven't had to turn the heat on. I do have neighbors that live below me however, so I'm sure that adds to it. The difference in temperature between the side facing the window and the side facing the room is astonishing. I don't have this done for all the rooms, but I'm contemplating.

Nice work! Our windows seal well and are double pane, but not low-e. The living room has tall South facing windows (similar to yours) that give good winter solar gain but lose a lot at night despite cellular shades. I've thought of making interior storms, but I haven't actually done anything yet. I'll be interested in if you have condensation problems on the glass in really cold weather -- I could see it getting better due to less convection bringing in moisture, or worse, because the moisture builds up day after day with no chance to escape. If there is a problem, perhaps a cloth at the bottom to absorb the water when the frost melts and runs down would be sufficient to protect the window sill.

I've been thinking about better curtains for the sliding glass door on the N side of the house. What did you get, Ricardo? Cell shades, quilted, etc, and any sealing method for the edges?
Greg

Greg:

These are the curtains (http://www.lowes.com/pd_309757-55802-6277052063BL_4294856889+4294832605_4294937087_?productId=3070531&Ns=p_product_prd_lis_ord_nbr|0||p_product_quantity_sold|1&pl=1&currentURL=%2Fpl_eclipse_4294856889%2B4294832605_4294937087_%3FNs%3Dp_product_prd_lis_ord_nbr|0||p_product_quantity_sold|1&state=R#prod-tabs) I used. I haven't used any particular sealing method as they are currently behind my couch and stick to the wall a bit. I'm sure they'll be more efficient once I decide to block them off for the rest of winter however.

We have a cat with claws.

Same here. They seem to behave themselves around the windows (I have yet to find any claw marks in screens) so we'll see.

Same here. They seem to behave themselves around the windows (I have yet to find any claw marks in screens) so we'll see.

I hope so. Our cat was actually just reaching and scratching the frame, I think, but put a hole in the plastic I'd put over it. There are a couple of rooms where it could still be applied.

I hope so. Our cat was actually just reaching and scratching the frame, I think, but put a hole in the plastic I'd put over it. There are a couple of rooms where it could still be applied.

cats increase emissions :D.

I've got pull down shades from JCPenny's that have a silver metallic backing to them. They're room darkening, and (in theory... or at least so sayeth the advert) are able to better keep in heat/cold depending on the time of year. Mostly though, it was for safety. There's no cords to hang a child from on them.

Time for some results! It took me about a month and a half to fabricate and install all 23 windows, working off and on. The simplest way to install them turned out to be little wire brads, which are unobtrusive and get the job done. I generally used one in each corner and a couple mid-span.

At the outset I was a bit concerned about condensation due to lower anticipated temperatures at the glass. This has turned out to be a non-issue. Condensation was a big problem on un-treated windows in October but hardly shows up at all now that the storms are installed. I imagine this has something to do with the lousy seal of the old windows letting moisture out while the storms limit the amount of moist air getting into the gap from the interior space.

Drafts are way down. Cold air used to cascade down the face of every window and across the floor, especially collecting in the den which is a step down from the rest of the first floor. This makes the house much more comfortable at a thermostat setting of 67.

As I mentioned before, this house is new-to-us so we have no idea what the baseline thermal performance was. (My guess: OK, not great.) The December energy bill brought good news, though. 87 therms of heating gas during a 916 heating degree day (base 65) month brings the heating load to just under 4.1 BTU/HDD/sq.ft. That seems to be in line with better-performing homes in the US. So I'm pretty happy. I see other items that need to be addressed, such as better insulation in the main attic, but that can wait until the weather turns back around.

Moderator:

Every time I try to click on the "curtains" link in post #12 I get a pop-up ad for Catepillar tractor parts.

Addendum: Ok, maybe it's due to the word "efficient" in the vicinity

That's just intellitxt ads. They can be a little annoying but probably better than a page riddled with obtrusive banner advertisements.

Moderator:

Every time I try to click on the "curtains" link in post #12 I get a pop-up ad for Catepillar tractor parts.

Addendum: Ok, maybe it's due to the word "efficient" in the vicinity

That's funny. I got the Volt Motor Trend Car of the Year.