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How To Diagnose Central Heating Systems

Home heating systems serve a simple purpose. But to achieve it they employ a surprisingly complicated set of components, some of which are prone to failure. Let's start with the simple and obvious (and cheap!) things first.

If you're getting no heat at all out the vent, check the pilot light and circuit breakers.

If your system isn't delivering enough heat, check filters first. Filters gradually become blocked with dust, animal hair, etc. They're cheap. Don't bother to wash, which ruins them anyway. Replace.

Check that vents are open and unblocked. Don't rely only on what you can see from a standing height. For high vents, get out the ladder and shine a flashlight into the vent. For low vents, get down to the cat's eye level.

If the vents are open and unblocked, you'll need to access the attic to check ducts. Many heating system ducts are in plain view on top of ceiling insulation. Check for obvious breaks. Turn on the system, then take a tissue and run it along any joints to check for air movement.

If you've ever had mice or rats (not unknown even in very well-to­do developments, especially when constructed near fields), you may have suffered damage. A mouse or rat can chew through a duct in a few minutes.

To repair breaks, paradoxically, don't use duct tape. It breaks down rapidly from temperature and humidity changes causing air leaks. It's also forbidden by building codes in some locales. Go figure. Obtain mastic (a paste, sometimes on tape) or similar sealing material.

Some systems can be improved by wrapping ducts with insulation. Many lose heat through conduction, even when there are no breaks. Check building codes and obtain the proper wrapping material.

If you hear squeaks or rattles there are several possible culprits.

Some heating systems are belt driven. Like the fan belt in your car they can stretch with age and temperature changes. Loose belts squeak because they slip along the pulley they ride on or help turn. Replacement is usually simple and inexpensive.

Rattles are usually the result of either loose screws connecting plates or ducts, or caused by metal expansion and air movement. There's little you can do about the latter, except wrap or replace with a different material.

Sometimes it's possible to make a small dent in the material. That edge helps make the surface more rigid. Take care not to break the part. Loose screws can be tightened, when they're accessible, but take care not to puncture wires or insulation.

It's possible that the heat pump on your system simply doesn't produce enough output to warm the size home you have. You can often see the ratings on tags on the pump, or check the documentation online. Upgrading is a job best left to a professional.

Similarly, ductwork may not be large enough to handle the air flow needed. Flow ratings should be 50-60 liters per second per kilowatt-hour or 400-500 cubic feet per minute per ton. Replacement can be carried out by a do-it-yourself'er, but is often more trouble than it's worth.

Obtain estimates from several sources. Go with someone trustworthy, not necessarily the cheapest. Cheap is always more expensive in the long run.

Remember that if you smell a gas leak, or have other heating problems, that utility companies will generally send a technician to the home for free. Take advantage of their services and have your system diagnosed. They have the skills and the tools to tell you whether you need to repair or upgrade your system.