Boost Your Furnace Output With This Simple Trick

It’s a common occurrence in the cold of the winter: One room doesn’t get as warm or as cool as the others. This  can happen for lots of reasons, from improper furnace sizing and dirty filters to failures in the air ducts that feed the room farthest from the furnace. If the furnace filters are clean and ducts well insulated, though, one likely reason for the cold room is that the blower isn’t pushing air fast enough to reach it.

Fortunately, there’s a simple fix — call it a hack — that will get that room as warm as the rest of the house. It only works on a gas furnace system that has a two-speed blower. If your furnace has a single-speed blower, you’ll have to try something else, such as adjusting the dampers, making sure registers are fully open, using space heaters or, in the extreme, getting a bigger furnace.

Here are a few signs of a furnace that’s struggling.

How This Simple Furnace Hack Works

To understand this trick, let’s look at the wiring on your furnace’s blower. To do this, you need to open the control panel and find the Integrated Furnace Control (IFC) board.

There are often five wire colors coming from your blower to your IFC. Each is associated with a different blower speed. Typical setups include these wire colors with associated blower speeds:

• Black: High;
• Yellow: Medium-high ;
• Blue or brown: Medium-low;
• Red: Low;
• White or purple: Common.

Typical systems use the high speed for cooling and the medium-high speed for heating. When the summer air conditioning season transitions to the fall heating season, we’re going to increase the blower speed and give the furnace a boost by switching the wires on the cool and heat terminals.

Family Handyman

Here’s the Procedure

To begin, turn off the power to your furnace. Mine has a wall switch. If there isn’t one in your home, turn it off at the breaker box. Most furnaces have a relay switch on the door cover. When you open the panel, it kills the power to the furnace.

On my furnace IFC, the black (high speed) wire is connected to the air conditioning (cool) terminal, and yellow (medium-high speed) is connected to the (heat) terminal. There are also red and brown furnace speed wires. These are connected to unused (park) terminals on my furnace, which doesn’t have more than two speeds, so I just ignore them.

To increase the blower speed, I remove the black wire, replace it with the yellow one, and then put the black one on the terminal vacated by the yellow one. Only swap these two wires. If you remove the common (white or purple) and place it on another terminal, it can burn out your motor, and that’s not how you want the new furnace season to begin.

FAQ

Should I ever slow down my furnace fan speed?

It’s not advisable to slow your furnace blower speed. If you do, you reduce the air flow over the heat exchanger, possibly resulting in overheating and eventually a shorter exchanger life span.

Is this hack safe?

If your furnace is like mine, with only two blower speeds and wires with the standard colors, it’s safe to follow this simple furnace hack as presented. Not all furnaces are wired with the same color wires, but if you can read the words “Cool” and “Heat” on the terminals, you can swap those wires no matter what color they are.

As long as you have a two-speed blower.

This isn’t a safe way to get a furnace boost if you have a variable speed blower that can self-adjust its speed (in which case, the “parked” wires are live). If you aren’t sure whether you have a two-speed or variable speed blower, don’t risk damaging it. Consult an HVAC technician for advice.