by Carey, James
Chapter 10
Heating, Ventilating, and Air-Conditioning Systems
In This Chapter
Keeping your furnace and boiler happy
Ventilating your home from top to bottom
Keeping your air-conditioning cool
We can describe heating, ventilating, and air-conditioning (HVAC) with just four words: hot, cold, in, and out. Or, more specifically: heating the interior when it’s cold outside; cooling the interior when it’s hot outside; drawing fresh air into your home to moderate temperatures and humidity; and venting moist, smoky, greasy, or stinky air from inside to outside.
And this brings us to the paradox of HVAC: These seemingly simple processes actually rely on some complex technology. As a result, there are very few maintenance tasks that don’t bring with them a high likelihood of killing the furnace, the air conditioner, or yourself. But the tasks that can be done by a do-it-yourselfer are easy and non-threatening. We’re confident you can do them without difficulty or danger — and they’ll make a huge difference in the efficiency, performance, and life of your system, whatever kind it is.
Making Friends with the Monster: Your Furnace
Most grown-ups never would admit it, but they’re terrified of their furnaces. A furnace is a big, complicated piece of machinery. But we’re here to tell you that there’s nothing to be afraid of. Your furnace is less mysterious and scary than you think. It heats up air or water, and then moves hot air, water, or steam around the house. It’s really that simple. In this section, we tell you what you need to do to maintain your furnace.
Taking care of a forced-air system
In a forced-air system, air is heated as it passes through the furnace (shown in Figure 10-1). A blower and a system of ducts take the warmed air throughout the house, and then cooled air is sucked into return ducts back to the furnace. You need to take care of your forced-air system to keep it running safely at peak efficiency.
Figure 10-1: A standard furnace.
The parts of your furnace and their locations may be different from the illustrations in this book. For specifics on your furnace, consult the owner’s manual that came with the furnace. (You probably filed it under “Manuals I’ll Never Look At.”) You may be able to get more information, a diagram, or even the manual, from the manufacturer’s Web site.
Inspecting and servicing a forced-air furnace
Forced-air furnaces must be inspected and serviced every year before the heating season begins. Follow these steps:
1. Look for the sticker that the last serviceperson affixed to the outside of the housing.
2. Hold a flashlight between your chin and shoulder while you write down the company name and phone number located on the sticker.
If you’re young and have great vision or if your furnace is located in a basement, attic, or garage that is well lit, you may be able to do without the flashlight.
3. Call that company to arrange for a professional inspection and service.
Kidding aside, it’s critically important to have a qualified, licensed heating contractor (or, euphemistically, a “home-comfort specialist”) inspect and service your forced-air system. Sure, you could save $90 by not having your furnace inspected at all, but a dirty, inefficient furnace costs you ten times that much per year in wasted fuel.
Even more important, a cracked heat exchanger or dislodged flue could fill your home with deadly carbon-monoxide gas. Plain and simple, an under-maintained or failing furnace is a danger to you and your family.
So what will the furnace serviceperson do? First, he’ll carefully inspect and check every critical component. Then he’ll perform dozens of maintenance tasks (lubrication, adjustment, and so on) that will help maintain, and even improve, your furnace’s efficiency and go a long way toward keeping it running well year after year.
Replacing the filter
The easiest furnace-maintenance task is replacing the filter. During the heating season, you should replace your furnace filter every month. If an air conditioner is part of the same system, you should change the filter every month year-round.
The filter, typically fiberglass or pleated fabric, is designed to take dust, dirt, pollen, lint, carpet fibers, and pet hair and dander out of the air, which keeps your home cleaner and keeps allergies at bay. Without all that stuff in the airflow and inside the unit, the blower motor lasts longer, and other parts of the heating system work better. The filter also prevents the air-conditioner evaporator coil (hidden within the unit) from becoming clogged — that’s a good thing, because when the evaporator coil is clogged, the air conditioner’s efficiency is reduced, and your utility bill runs sky-high.
If your furnace uses a standard 1-inch disposable filter, don’t bother buying fancy, ultra-high-efficient filters. The pleated kind is fine. The filter is tightly woven and won’t let large particles pass, and the pleats double the filtration area, resulting in less stress on the system blower. Unless your home is hermetically sealed, you never open a window or a door, and you’ve removed all inside allergy sources (which is extremely unlikely), those mega-filters don’t provide benefits commensurate with their significantly higher cost. And they may reduce airflow and cause the blower to strain to push air through their thicker, tighter filtering medium. Don’t believe us? Ask your serviceman. He’ll back us up on this.
Why do we like pleated filters better than the typical spun-fiberglass filters? Because they actually work. You can see for yourself: Lay a standard fiberglass filter flat on a table, and shake some table salt onto it. If the filter allows salt to pass through (which it will), how can it snag a microscopic grain of pollen? Now, perform the same experiment using a pleated filter. Look mom, no salt! A pleated filter does add some resistance to airflow, but not enough to make a difference.
Don’t buy 1-inch filters one at a time — get a whole case. They’re cheaper by the dozen. What’s more, the box sits by the furnace and reminds you to do the monthly change. And you’ll never miss a change because you don’t have a filter on hand. Want to make extra-sure you don’t forget? We have a friend who opens the box as soon as he gets home from the store and labels each one with the month in which he’ll install it. We think that’s smart. Try it!
To replace the filter, follow these steps:
1. Locate the filter slot.
You can usually find the filter near where the cool air enters the furnace — in the cold-air return duct, or at the entrance to the blower chamber. Though redundant, sometimes you’ll find filters in both locations — typically a washable filter at the furnace and a replaceable fabric filter at the cold-air return. (If it’s not where the cool air enters the furnace, look in the main return air register, which is on the wall or ceiling somewhere in your home.)
2. Slide out the old, dirty filter.
You may have to jockey it back and forth a bit.
3. Remove the wrapping from the new filter (if any), and locate the airflow arrows on the side.
4. Position the filter so that the airflow arrows point toward the blower and with the flow of cold air.
5. Slide in the new filter, being careful not to dent, deform, or tear the cardboard frame.
6. Check to make sure the filter is snugly in place and all the way in its slot.
Some furnaces have more-complicated, wider filters that slide into a plastic housing that, in turn, slides into a wide slot. Follow the manufacturer’s instructions for replacing the filter, and then slide the housing into place.
Other furnaces have permanent filters. These filters usually don’t need to be cleaned as often as the less sophisticated fabric filters. Cleaning instructions usually are affixed near the filter on the side of the furnace or in the owner’s manual. Consult a pro when in doubt.
Cleaning the blower compartment
The blower is a large “squirrel cage” fan (see Figure 10-2) that pushes air out through the ducts to the registers throughout the home. The blower also draws air through return registers into the ret
urn ducts and into the unit to be reheated or re-cooled and recirculated. You need to clean it twice a year. Here’s how:
Figure 10-2: Inside your furnace.
1. Before you do anything, turn off the power to the unit.
A service/emergency switch may be mounted on the furnace itself or near it. If you can’t find the switch, turn off the power at the circuit breaker or fuse box.
2. Open the access panel on the front or side (if it isn’t already open to change the filter).
You may need a screwdriver or socket wrench to do this.
3. Locate the blower, and remove the blower access panel.
The blower will have an access panel that is held on by slip-fit hooks or retaining screws.
4. Use the vacuum cleaner with the upholstery brush attachment on it to remove any dirt, lint, and dust bunnies you find.
5. Replace the blower access panel.
6. Replace the access panel, making sure it’s in correctly and tightly closed.
7. Turn on the power to the unit.
Whenever you’re poking around inside your forced-air unit, be careful not to disturb any of the small wires inside the unit. Most systems have low-voltage controls, so you can’t get zapped, but if you inadvertently dislodge a control wire, the system may not come back on.
Checking, replacing, and adjusting the blower-fan belt and pulleys
If your furnace is not a newer model, you need to keep your eye on the blower-fan belt. (If you have a newer furnace, you won’t be able to find the belt or a fan — the blower is driven directly by a motor.) A worn, wimpy belt can fail at any time, and it always seems to do so at the most inconvenient time — like midnight on Christmas Eve. A loose belt won’t fail, but it will make a squealing noise that can drive you crazy. More important, a loose belt costs you money because, if the belt is slipping, the blower doesn’t turn as it should. Plus, if the blower isn’t blowing hard enough, you’re getting weaker airflow and less hot air for your money.
To check the fan belt, turn off the power to the unit, remove the access panel, and look for fraying, cracks, slippage, and so on. If the belt is frayed, cracked, or otherwise worn-looking, you must replace it as soon as possible. If the belt is loose (with more than 1/2 inch of give), you must tighten it.
You can also inspect and adjust the pulleys. The belt rides on two pulleys: one connected to the motor and the other connected to the blower. The pulleys often have lubrication points that should receive a few drops of oil each time the system is serviced.
You can address all these problems by taking the steps in the following sections.
Replacing the belt
To replace the belt, follow these steps:
1. Turn off the power to the unit.
2. Remove the access panel (if you haven’t already done so).
3. Loosen the adjusting bolt on the motor just enough to get some slack.
4. Slip the belt off the pulleys.
5. Go to your local hardware store or home center and buy two replacement belts.
Take the old belt with you to make sure you get the right replacement. Keep the extra belt in a plastic bag on a nail by the furnace. That way, you have one on hand when you have a middle-of-the-night, all-the-stores-are-closed, the-house-is-freezing, blower-fan belt emergency.
6. Put the new belt back on the pulleys and tighten the adjustment bolt until the belt has only 1/2 inch of give.
7. Replace the access panel and turn on the power to the unit.
Tightening and adjusting the belt
The belt should have no more than a 1/2 inch of give when you press on it with your finger. If it gives any more than that, you need to tighten it.
To tighten the belt, follow these steps:
1. Turn off the power to the unit.
2. Remove the access panel (if you haven’t already done so).
3. Slightly loosen the motor adjustment bolt.
4. Slide the motor a little bit at a time to increase tension on the belt until you have about 1/2 inch of give.
Don’t over-tighten the belt. A too-tight belt will damage the motor and fan bearings.
5. Double-check to make sure the belt has 1/2 inch of give.
6. Tighten the bolt.
7. Replace the access panel and turn on the power to the unit.
Checking and adjusting the pulley alignment
When the pulleys aren’t aligned, they can twist the fan belt and cause it to wear quickly or even break. To check and adjust the pulley alignment, follow these steps:
1. Turn off the power to the unit.
2. Remove the access panel (if you haven’t already done so).
3. Place a ruler against the pulley faces.
4. Check to see that the pulleys line up perfectly and that the belt travels between them without twisting even a little.
5. If the pulley alignment is off, slightly loosen the motor-pulley mounting bolts, adjust the motor pulley to align it with the other pulleys, and then retighten the mounting bolts.
6. Recheck the alignment using the ruler and readjust as necessary.
7. When the alignment is perfect, replace the access panel and turn on the power to the unit.
Taking care of your ducts
Ducts are square or round metal tubes in the ceiling, walls, and/or floors that transport air from the furnace to each room in the house. A leak in a duct can allow massive amounts of heat into the attic, crawlspace, or basement. Keeping the ducts tightly sealed ensures that all the expensive heated air coming from the furnace gets to where it belongs.
Leaks aren’t the only issue with ducts, though. Even with a serious commitment to filter replacement, the inside of ducts eventually get a coating of fibers, lint, dirt, allergens, mildew, grease, and even bacteria.
Checking the ducts for leaks
If you have access to your ducts, checking for leaks is easy:
1. Follow each duct from the furnace to its termination, paying special attention to the joints between segments.
2. Look for fuzz that has been forced through joints, or feel for warm air coming through gaps.
You may need to pull insulation away from the joints and visually inspect them. Dark stripes in the fiberglass insulation is a telltale sign of a duct leak below the insulation. Other big leak locations are around the boot (the piece where the duct penetrates your wall, floor, or ceiling).
If you really want to identify how leaky your ducts are, bring in a pro to perform a duct pressure test. This test involves pressurizing the entire duct system, which determines how much of your heated or cooled air is being wasted. A duct pressure test usually runs in the neighborhood of $100 to $200, depending on the size of your home and where you live.
Sealing leaks
If you find any leaks during your inspection, seal them:
If your leak is below the duct insulation, seal it with metal duct tape. (not the fabric duct tape that you’re used to using and that you can use on just about anything other than ducts).
Alternatively, use an elastomeric duct sealant (available at most home centers or hardware stores). When dry, the elastomeric duct sealant provides a rubbery, airtight seal at all joints and seams; it bonds flexible ducts to metal duct fittings.
You can also call in a heating pro to do the job for you.
If your leak is around the boot, remove the register cover and caulk the joint between the boot and the wallboard.
As an alternative, you can use a butyl-backed tape to seal the gap — this method is the one that the pros use. Be sure that you position the tape in the right place because, after it’s applied, this stuff sticks like heck. Use a utility knife with a sharp blade to trim any tape that may be exposed after replacing the register cover.