This item on the home efficiency list is likely the most time consuming and will involve the most work - and a lot of it will be grunt work. This project will involve you searching for air leaks, identifying which potential leaky spots are actually leaking, and fixing those leaks. Where can leaks occur? Just about anywhere you have a transition from the indoor space to unconditioned space (wall cavities, the attic, etc.) or the outdoors. Windows, doors, switch and plug outlets, recessed light fixtures, and many other things can be a source of air leaks. Fixing those leaks, and thereby reducing the flow of expensive conditioned air to areas that do not need or should not be conditioned, will go a long way to reducing your energy demand.
The Home/Thermal Envelope
The home or thermal envelope refers to the parts of a structure that separate the indoor living space (bedrooms, bathrooms, living rooms, kitchen, etc.) not only from the outdoors, but also from spaces under the home's roof that are not air conditioned or heated. These unconditioned spaces include attics, unimproved basements, crawl spaces, wall cavities, floor cavities (such as those that separate floors in multilevel homes), and the like. While they may share some common components, the thermal barrier is different from the weather barrier of a structure. The weather barrier includes things like the roof and exterior walls, and its purpose is to keep the weather out by blocking rain, sun and wind. Exterior walls are a good example of a structure that is both a weather barrier and a thermal barrier. The roof, on the other hand, is usually not part of the thermal barrier, because in general the roof is not in direct contact with a conditioned space - an attic usually separates the two. The ceiling between the conditioned space and the attic, however, is definitely a thermal barrier.
Obviously, conditioned air (whether that air is heated or cooled) requires energy and costs money to generate. When conditioned air flows to unconditioned spaces where it isn't needed, you waste the energy consumed and money spent to condition that air. By defining and sealing your thermal envelope, you minimize the flow of that conditioned air to where it isn't needed, thereby keeping it in the spaces where you want it. This means you condition less air, which in turn means you reduce the demand on your conditioning units, which in turn lowers your energy consumption and utility bills.
It is important to note that some air transfer is actually desirable. For air quality and moisture/humidity purposes, you do want and need some air exchange, and you do not want to make your envelope too tight by totally eliminating air transfer. But you do want to try to control it in the interest of energy consumption. Newer homes are built so tight that some of them actually require fresh air ventilation systems. Older homes, on the other hand, will usually not require them even if you do undertake sealing projects - mainly because it is highly likely that you'll never find and/or eliminate all of the leaks. As such, I will not cover fresh air ventilation here in my babbles.
Another important note: in general, most types of insulation do not stop air flow. Although all parts of the thermal envelope should have some type of insulation, the envelope should also have some type of barrier to minimize air flow, and insulation by itself doesn't cut it. The primary purpose of insulation is to provide a thermal - and in some cases, radiant - barrier that stops the transfer of convective, conductive, and radiant heat between conditioned and unconditioned spaces. Other tactics should be used to minimize the transfer of air between those spaces.
Want an analogy? Consider a fleece or knit sweater. It will keep you warm when it is cold outside because it insulates your body from the cold air and helps retain the heat. But if you add a breeze to the cold, you're still cold even when wearing a sweater because the air moves right through it. Now put a windbreaker on top of the sweater. That stops the breeze and the flow of air through the sweater, and you're warm again. The same principle applies to home sealing and insulation: insulation is the sweater, and the your home sealing projects are the windbreaker. Stopping air leaks through the home envelope complements the effectiveness of insulation, and they definitely work in concert together.
One other item to consider with regards to insulation. Do you have any walls that adjoin an interior but unconditioned space, such as an attic? If so, you need to make sure those walls are insulated. However, rolling and securing batts between the studs is not enough. A wall only reaches it full insulation capacity when the wall structure is complete. With just insulation, it is only two-thirds complete: the interior drywall and the insulation. You need to complete the wall structure by adding the "exterior" portion of the wall to the wall structure. This doesn't have to be anything fancy or expensive. All it has to be is a piece of foam board or exterior sheathing board nailed to the studs on top of the insulation. The only thing you need to make sure of is that whatever board you do install, make sure it has a vapor barrier of some sort, and that the barrier is facing towards the unconditioned space (rather than towards the insulation).
Where Are the Leaks?
Finding and fixing air leaks between conditioned and unconditioned spaces can be a challenge, time consuming and in some (but not all) cases expensive. For instance, windows and doors can be a huge source of air transfer, but replacing them can involve major bucks and may not be worth the investment in terms of direct energy savings. These items are most definitely the easy culprits to identify because they're large and they separate the indoors from the outdoors. But they are definitely not the only culprits. The best way to approach any sealing project is to fix the biggest leaks first - because fixing those makes the biggest difference the quickest - and then work your way towards the smaller leaks. Let's dig a little deeper.
Another large, but maybe not so obvious channel for air to flow: attic access hatches. If these open up into the conditioned living space, they can transfer a lot of air between the two spaces. These hatches could be the fold-down attic stairs, half- or full-height passage doors through a wall in a bedroom or closet, and other types of openings. Sealing these passageways should be a top priority because they're big holes.
Other relatively large air leaks can occur in and around the attic space. Here's a list of some common areas to look for leaks:
- Forced air system ductwork
- Gaps between air vent boot assemblies and ceiling drywall
- Drop soffits such as those above kitchen cabinets or some bathroom vanities
- Any place where the ceiling changes height in a room or between rooms
- Recessed lighting canisters that punch through the ceiling into the attic space
- Ceiling electrical service boxes (like those from which ceiling fans and light fixtures hang)
- Ducting and chimney chases
- Areas around plumbing vent stacks
- Wiring passage holes as they go down between walls
- Gaps between bathroom ventilation fans and ceiling drywall
- Service penetrations for plugs, light switches, cable, phone jacks and the like
Unfortunately, finding and fixing these types of leaks is a cramped, dirty, and uncomfortable project that will take some time and a lot of effort (not to mention knee pads). But sealing these leaks is extremely important to reducing energy consumption and increasing comfort in the living spaces.
Sealing the Leaks
Once you've identified the leaks, it is time to seal them off. We'll go step by step on this, looking at some of the examples mentioned above.
Recessed Lighting & Ceiling Electrical Service Boxes
You've all seen them: those can lights that poke up through the ceiling that contain flood or spot light bulbs. Older canisters are huge sources of air leaks because the heat generated by the bulb needs to go somewhere. Also, because of the heat generated by the bulbs, older canisters cannot have insulation or any other material within about 3 inches of the canister housing up in the attic. If yours are older and you can access them, you need to change them! Newer recessed lighting is rated ICAT, which stands for Insulation Contact, Air Tight. These new fixtures can be safely covered with insulation, and they do not need or allow air flow from the conditioned space up into the unconditioned space. Once installed, you should caulk around the fixture to seal it up to the drywall.
You know the electrical boxes in your ceiling where you hang lights or fans? Where the wires come through? You need to seal those off as well. Caulk around the perimeter of the box itself, then use caulk to seal all the little holes you can see in the box. And don't forget to caulk around the wires that penetrate into the box.
Soffits and Ceiling Height Changes
Drop soffits are those drywall extensions you've seen in kitchens that go from the top of cabinets to the ceiling. You can also see them in bathrooms and other applications. Some will even contain recessed lighting fixtures. If accessible, these areas should be inspected and sealed as best as possible. Sealing larger openings will require foam or other backer board to be installed. Smaller openings should be sealed with expanding foam and/or caulk. Once sealed, don't forget to insulate!
Ceiling height transitions can also pose leaking problems. Any leaky or open spaces should be covered with foam or backer board and sealed with foam or caulk. Again, don't forget insulation!
Chimney/Ducting Chases and Plumbing Vent Penetrations
If you have a chimney or other type of flue that penetrates from the conditioned space into unconditioned space (and you can access it), you need to make sure it is sealed up. This will take a little special work, as you have to be careful due to the heat produced. In most cases, you will need flashing to butt up against the brick or flue, and be sure to keep any potentially flammable material a minimum of two inches away. Attach the flashing to the rough opening's framing with nails or staples and then caulk the joints with high-temperature silicone caulking or furnace cement.
Ducting chases or other larger penetrations should be sealed as well, but you don't need metal flashing. For larger holes, foam board or duct board can be used to cover the holes. Final sealing (or sealing for smaller holes) can be accomplished with silicone caulk or expanding spray foam.
You also need to seal the areas where plumbing vent pipes penetrate through from the areas below. Spray foam or caulk should take care of most of these. You don't need to worry about sealing up the area where the pipe penetrates from the attic to the outside.
Wiring Holes & Penetrations
In many homes, a lot of the wiring makes its long runs in the attic, and only penetrates into a wall where the service is needed. Even if you cover the plates using those foam inserts, you should still seal the hole where the wires penetrate down into the wall cavity. This can help prevent unwanted heat from circulating down between the wall's studs where the wiring penetrates, thus warming the walls. Keeping this circulation down can further reduce cooling loads. It won't be much, but every little bit helps.
Foam inserts, you say? Those are switch and wall plate sealers like these from MD Products. These are simply stamped foam inserts that go behind the wall plate covers. They can be cut and modified with scissors to fit just about any switch or plug application you have. And remember: these should be installed on both interior and exterior walls! Lots of air can leak into unconditioned spaces through all those plugs and switches, so do them all regardless of what wall they're on. These can be had for about a quarter each.
Sealing Ductwork and Vent Boots
Some of the largest air leaks can occur in your forced air system's ductwork. As much as 30% of your conditioned air could be escaping into unconditioned spaces before it even enters your living areas! In many cases, ductwork will have become disconnected, torn, punctured or otherwise damaged. When this happens, you're blowing expensive air meant for your living space right into the attic or other unconditioned space. One of your sealing project's top priorities should include inspection and repair of leaking ductwork. Finding the larger leaks should be relatively simple for the ductwork you can access. Simply turn on the blower motor and let the system circulate air through the system. Then climb up there and feel around all seams and connections (or disconnections) and evaluate the best way to repair and seal them up. That could include some duct replacement, especially if it is flex duct that has been damaged. If you are unsure what to do or uncomfortable repairing or replacing damaged ductwork, you should contact a contractor that specializes in ductwork.
Many systems will have trunk line ducts, from which smaller flexible ducts run to the register vents. If you don't have trunk lines, your flex-duct will connect directly to the plenum, which is directly attached to your air handler. First, inspect your plenum and trunk lines for leaks. Check all connections and seams and reconnect, repair or replace, and seal them as necessary. Any holes should be covered and sealed, and connections of flex duct to the plenum or trunk line should also be sealed with duct mastic.
IMPORTANT NOTE: Everyone has heard of and used duct tape for one thing or another, and it is definitely one of man's greatest inventions. However, DO NOT use duct tape to repair leaks in your forced air ducting system!!! I know it sounds weird; I mean, it is DUCT tape, right? Well, while it will work temporarily, the adhesive on duct tape will quickly dry out and fail, and and as such, your leak repairs will also fail. So never use it for duct repairs or assembly. You need to use duct mastic, which is a paste. While it can be messy, it is relatively easy to work with, remains flexible even when it dries, and is a permanent fix to ducting leaks. Larger gaps and holes should be covered with aluminum ducting tape (either with or without adhesive on one side - again, not traditional duct tape), and then sealed over with duct mastic.
Don't forget your ductwork includes the vent registers that penetrate through the ceiling or wall and allow delivery of conditioned air to the living space. This is another interface that should be sealed - particularly the junctions between the metal supply air boots and the drywall. Why is this important? There are typically gaps between the metal boot and the drywall. As forced air comes out of the vent, it produces a venturi, or vacuum, effect. As the air exits the vent, it causes negative pressure around the boot, and that negative pressure will suck air and dust from the unconditioned space on the other side of the vent boot and into the living space. The best way to seal this off is with duct mastic. Be sure to let the mastic dry before reinstalling your vent registers, otherwise the mastic could gum up your adjustable vents or make them extremely difficult to remove during your next painting project.
Attic Access Stairs/Doors/Hatches
My old Katy house had a split-level attic, and as such, it had two attic entrances. One was upstairs, and one was downstairs in the utility room, and the stair hinges on both of them were weak. Previous owners had tried to close the gap with latches, but these still allowed a lot of air to pass through them. So much air was leaking around the upstairs access stairs that I could reach my hand up to the ceiling and feel an at least 10 degree temperature increase in the span of about a foot from the ceiling.
After seeing one in action at my parent's home (which I now own), and after doing some research, I purchased two Attic Tents. These little gems are awesome! They solve two problems: they stop the majority of the air transfer through the attic access hatch, and they also provide a measure of insulation. Before when I would pull down my attic stairs, I was greeted with a blast of hot air, and as mentioned, some of that hot air from the attic was leaking around the stair door. The air leakage was virtually stopped, and I could feel virtually no temperature change when I stuck my hand up to the ceiling around the access door. When you need to get up in the attic, you just pull down the stairs, climb up, unzip the tent's flap and toss it back. You climb up and do your business up there. When you're done, climb down, pull the flap back over the opening and zip it back up. Fold up the stairs and close the door, and you're done. Sweet.
Attic Tent's site says all you have to do is set the tent in place and staple it down. To further block air transfer, I went one step further by following the example set on the folks' house. I used water-based duct mastic to seal the transitions between the tent's material and the wood ceiling joists and stair unit framing. If you purchase and install one of these, I highly recommend you do the same. Total installation time for both units, including sealing them with the duct mastic was about an hour and a half. Supplies were a staple gun and staples, duct mastic and a putty knife. Add in a little elbow grease, some paper towels for cleanup, and a minor amount of monkeying around in the attic (most of the install I was able to accomplish standing on the access stairs) and that was it! Here's a picture of an attic tent installed on the upstairs attic access at my old Katy home.
Also, you can buy the Attic Tent directly from Insulsure's web site, but you'll pay top dollar for it there if you do. The model I needed - the AT-2 - lists on their site for $190. By shopping around, I was able to purchase mine online from Energy Federation, Inc. for $115 each. They've also got some other pretty cool stuff out there, too, so check them out.