Dual-pane windows were invented in 1935 but weren’t widely used in the United States until the 1950s. Our windows were manufactured by Andersen and they are true divided-light single-pane casement windows. When the house was built, fuel oil was inexpensive, so it was more cost-effective to simply burn more oil than it was to invest in insulation and very costly dual-pane windows – not when you consider that our house has 40 windows incorporating a whopping 136 separate window sashes!!

A single-pane window has an R-value of 0.91. Dual-pane windows usually have R-values starting at 2.0, and super-efficient triple-pane windows can achieve R-values greater than 3. But there’s more to windows than just numbers.

There are three methods of heat transfer: radiation, conduction, and convection. Radiation is the heat you feel from the sun; it warms objects. Conduction is heat that passes through materials; nature will always try to balance the heat on both sides of a barrier.

The last method is most important when considering windows: Convection. When the warm air in a room hits the cold window glass, it loses heat. The now-cold air sinks down, pulling more warm air in behind it. This creates what is called a Convection Current, and it creates drafts that can make a room much less comfortable.

With heating oil hovering at the $4 mark, we started looking for ways to reduce the drafts in our old windows. One of the methods we tried last winter was to cover the window screen inserts with insulating window film; the kind you attach with double-sided tape and shrink to fit with a hair dryer.

These worked, sort of. The main problem was that the air gap they created was nearly 2 inches wide – plenty of space for a convection current to be created in the gap. So we were still losing heat; it was now just a two-step process. They tended to wrinkle, and were prone to tearing. Also, covering the screens meant we couldn’t open the windows for ventilation.

A few months ago Bob started researching other options. He had decided that plexiglass inserts were going to give us the best results, but the issue was finding a supplier that could both cut to very precise tolerances (to the nearest 1/32^nd inch), and at a price that wouldn’t require a second mortgage. He finally chose TAP Plastics.

So we started measuring the windows. A regular measuring tape simply wasn’t going to be accurate enough, as we had to be as precise as possible so we could get the tightest fit. Bob found this ruler at the hardware store and it was the perfect tool for measuring inside dimensions.

This is a Lufkin X46 Extending Ruler. It has a brass extension bar that lets you get amazingly precise inside readings. To make sure we got the most accurate measurements, we each took them independently and then compared numbers. If we didn’t get the same numbers, we went back and re-measured. A lot of work, but the end result would be worth it.

We then ordered the plexiglass. For most of the panes, we chose 1/8” thick clear plexi, so there would be less chance of wobbling or warping. For the smaller panes (the ones in the French doors, which we would have to do individually), we chose 3/32” plexi.

Installation

Each piece of plexiglass was protected by two sheets of blue adhesive plastic. To get started, Bob would peel the plastic off one side of the plastic, and then set it in place in the sash, right up against the muntins. This would leave a gap of between 5/8” and ¾” – just right to create a true dead air gap.

While pressing the plexi against the window, Bob started to peel back the front protective plastic. To hold the plexi in place, he used these little things:

They’re called glazier’s points, and they’re meant to hold panes of glass in window sashes. They’re usually covered up by the window putty. In our case, we were going to use them to hold the plexi tightly against the sash. They are just pushed into the wood frame with a flat tool, like a paint scraper. Each sash required about a dozen points.

Once the plexiglass is installed, it is hardly noticeable:

So, did it work?

We’ll let the pictures tell the story.

This is a three-sash window on a north-facing wall. The left sash is the plain single-pane window glass. The center sash has the screen insert with the window film applied to it. The sash on the right has the plexiglass installed in both the lower and upper sashes. It’s a huge difference!

Here’s another example.

This is a French door on the opposite wall of the same room. Only one pane has the plexiglass on it. Can you guess which one?

We now have this plexiglass insert in every single-pane window in the house. The total cost for the plexiglass was about $1800, plus another $40 for many packages of glazier’s points (we’ve managed to clear out the stock in all three area hardware stores). Applying the plexi took about five minutes per sash; it took more time to wash each window thoroughly before the application!

Would you believe… neither?

Calculating the cost savings for replacing either an HVAC unit or windows can be tricky, but it’s worth doing the math to make sure you’re spending your improvement dollars wisely.

Keeping your cool

Let’s take the example of an older gas furnace/AC unit. If the average summer electric bill is $300 and the average winter bill is $175, then the AC component of the electric bill is around $125 per month. Older units can have efficiency ratings of around 8, and new ones are rated at 16, so in theory, you could cut the AC component of the electric bill in half. But how much are you saving, really?

In the DC area, air conditioning is used for three to four months of the year. Even if you upgrade to a unit with double the efficiency of the old unit, your total savings could be surprisingly small:

Old unit: $125 x 4 months = $500 electricity cost for AC

New unit: $75 x 4 months = $250 electricity cost for AC

So the new unit will save you $250 per year. Assuming you spend $6000 on the new unit, the payback period could be as long as 24 years… much longer than the expected lifespan of the new equipment. If your existing equipment is still working, a more cost-effective option is regular maintenance. Have it tuned, change the filters regularly, and make sure all ductwork is sealed properly.

Uninsulated ductwork in attics leads to excessive energy loss and increased utility bills.

What about windows?

Window efficiency is expressed as “R value.” An old single-pane window has an R value of one; if it has a storm window, it goes up to two. A new modern double- or triple-pane insulated window can have an R value between 3 and 6. Replacement windows start at around $250 per standard opening (and that would be for vinyl single hung inserts with an R value of 3), and an average house has about 12 windows, replacing them all can easily exceed $3000. Full replacement with wood-framed windows can easily be triple that. That’s a lot of electricity cost to recoup.

Simply closing the latch on this double-hung window will help lower energy bills.

Before choosing to replace windows, make sure the gaps around the frames are well-caulked. Fix any loose latches or hardware so the windows close tightly. Add operable draperies to cut down on heat gain/loss.

One upgrade that makes sense

An item that is often overlooked as an energy hog is the refrigerator. A fridge that is only 5 years old may be using twice as much energy as a newer model, and fridges use much more energy than people think. After all, they are running all the time! Many houses also have a second fridge in the basement, often containing just a few items. These smaller secondary fridges are usually bigger energy hogs than the one in the kitchen. Replacing an inefficient fridge with a new Energy Star rated model could pay for itself in energy savings within five years.

The broken icemaker and stains on the gasket indicate this fridge might be a candidate for replacement.

You can check whether it makes sense to replace your own fridge by using the government’s Energy Star Calculator.

Air Leaks

Some common sources of air leaks

Unintentional air leaks can suck cool air out of living spaces, drawing in more hot air from outdoors. Even tiny gaps around recessed light fixtures, vents and other penetrations can add up to a lot of leakage. A simple way to track down air leaks is to light a stick of incense and go through the house, checking around every wall penetration (electrical switches and outlets, exterior doors and windows, ceiling lights, etc.). When you find a draft, plug it with insulation, caulk or weatherstripping.

Insufficient Insulation

Insulation was swept aside for access and not replaced.

In the DC area, the minimum recommended insulation level is R-38. R-40/50 is better, and that is 14” of Fiberglas or 10” of cellulose at a minimum, with no paths, gaps or voids. A single small void can reduce the overall R value in the entire attic.

Contractors working in attic spaces sometimes clear footpaths through insulation and fail to replace it or fluff it back up as they leave. Settling is also an issue; you should inspect your attic regularly to make sure the insulation is in place.

One common weakness in attic insulation is the access hatch. It rarely has the recommended insulation, and that means a big reduction in overall attic protection. One way to insulate the hatch is to construct a simple open-bottomed box out of rigid foam insulation and silver foil tape (which is rated up to 150 degrees). This keeps the access hatch insulated, and is easily moved aside when you need to get into the attic.

Inadequate Ventilation

A powered attic fan can help your HVAC efficiency

If the attic is 150 degrees, and you want the living space at 72, the insulation better be in really, really good shape. I have recorded temperatures above 150 during my inspections. The passive ridge vents just don’t hack it in our area; you really need active ventilation, meaning a powered fan, to keep the attic between 110 and 120 degrees or cooler.  Look at it this way: If you have an AC/Heat pump in the attic, and its metal chassis is at 150 degrees, how is it going to pump out 65 degree air without spinning the electric meter really fast?

Lack of Maintenance

If your HVAC unit is in the attic, it needs regular attention. Air filters need to be changed every 30 days.  AC units must be serviced each spring to make sure they have the right amount of coolant or you will have high electric bills and the unit won’t stand a chance of keeping up on these triple-digit days.

Design Considerations

The design temperature in the DC area is 95 to 100 degrees. This means that units are designed to be working at 100% capacity when the outside temperature is 95 to 100degrees and the inside “middle of the room” temperature is 78 degrees. If your unit is cycling on and off on a day like today, there is a problem. This could indicate that the unit is too big and is cooling the house too fast and not dehumidifying the house, so it will be cold and clammy because it is not running long enough to remove the humidity. Units need to be running 14-20 minutes before they reach peak dehumidification. If it cycles before that, you have a problem.

If your unit is undersized, you will not be able to cool the house down no matter how long the unit runs. This is why it is critical to have a properly-trained technician assess your home’s heating and cooling needs. Ask for a “Manual J” assessment; this is an industry standard survey that measures the square footage of window and wall space, along with other factors, to determine the house’s requirements.

A lot of the efficiency of an HVAC unit also hinges on proper installation; I have seen too many houses with improperly installed systems and/or faulty ductwork.

Practical Issues

The temperatures we’re seeing in the DC area are outside the normal range, and it really isn’t practical to install HVAC systems that can handle occasionally extreme temperatures. Doing so means the unit won’t operate efficiently on the more normal days, and will just increase the operating and maintenance costs.

Even though there were no indications of water intrusion in the interior of the house, it was obvious that there was ice damming going on.

Water from ice dams is seeping down the exterior wall

Water has penetrated through the eaves on this house, and is seeping down the brick exterior, where it saturates the brick and refreezes. This can cause damage to the brickwork, shortening its life.

This bedroom had a cold spot in the corner.

The ice dam evidence outside prompted Bob to pull out his Thermal Imager. Taking thermal images is not part of a regular home inspection; in this case he was using it to find possible water damage inside. Although he didn’t find water damage, he did find some examples of why the house had ice dams.

The bedroom corner lacked any insulation

The thermal image revealed a joist space on an exterior wall without any insulation at all. This patch could allow warm air to escape into the attic space and cause the snow on the roof to melt from underneath.

Notice the snow has thinned between these two dormer windows.

Snow that melts unevenly can be a clue for where to look for missing insulation. Here, the space between these two dormer windows was a closet.

The roof over this closet had less snow than other areas.

The thermal camera revealed the issue:

Missing insulation in the closet ceiling

Another joist space was missing insulation. This space would be vulnerable to water damage.

Cold stripes on the ceiling

Thermal pictures of one ceiling revealed cold stripes. When Bob got into the attic, he found the source.

Areas around the joists were not insulated properly

Batts of insulation were compressed around trusses, leaving bare spots over some of the joist areas. The batts should have been cut to fit around the trusses. Also, whenever insulation is compressed, its R value is reduced.

You don’t necessarily need a thermal camera to find gaps in your insulation. All you need is a really cold day. Run your hand along the walls and ceilings, especially at the edges and corners. If one area feels cooler than the others, there’s a good chance it’s underinsulated.

How an ice dam works

Ice dams can happen any time snow falls on a sloped roof, especially if the gutters are clogged with debris and the attic is poorly insulated. Heat from the interior melts the underside of the snow pack; this water flows down the roof and is stopped by a buildup of ice at the edge. With nowhere to go, the water pools at the edge and rises under the shingles, where it then can flow down through the attic space and into the ceilings and walls of the house.

Heat from the house can get into the attic several ways.

Houses with very shallow or non-existent eaves are more likely to experience ice dams, as the edge of the roof is directly above the heated living space. Also, if you have recessed ceiling lights, they may also allow heated air to leak into the attic.

Once you have ice dams, there’s not really much you can do about them.
After the snow melts, though, you will need to do several things to prevent them from happening again.

• Insulate the attic, especially at the eaves. Any insulation that got wet from a leak must be removed and replaced. The best thing is to insulate the floor of the attic, so heat from the house doesn’t penetrate the attic. This will also reduce your heating bill. Keeping the attic cold during the winter will prevent the snow on the roof melting from the inside out.
• Keep your gutters clean. Have them inspected and repaired, if necessary. Gutter helmets and other debris guards will not protect against ice dams.
• Have a roofer install ice and water shield underneath the first few courses of shingles on your roof. This will create a waterproof layer of protection for the lower edge of the roof, so any accumulated water that gets under the shingles can’t penetrate to the sheathing.

A waterproof membrane under the shingles can prevent water damage