Understanding How Your Furnace Works

How your furnace works | CoolHeat Comfort Systems

 

With heating season upon us in Ottawa, Prescott-Russell & SD&G having a better understanding of how a furnace works will help prevent unexpected Furnace Repairs.

A lot of home owners in our service area like to be able to do a lot of repairs themselves and having an understanding of how a furnace works will help with that.

 

Here's the basic sequence of operation for a high-efficiency furnace:

*Before start-up*

1. Thermostat calls for heat: When the temperature in the room(ambient temperature) is lower than the number you set(setpoint), the thermostat sends an electrical signal to the furnace control board to begin start up operation.

*Furnace start-up*

2. Inducer motor start-up: The inducer motor (also known as the ventor motor) starts, creating a negative pressure in the furnace. This creates a positive pressure through the plastic venting pipes and blows to the outside. You've probably seen the white or black(older venting system) sticking outside your home.

*SAFETY CHECK*: The pressure switch will confirm there is properly flow in the exhaust system, and allow the next step to happen.

3. Gas valve opening: The gas valve has a big magnet in it, that will 'energize'; opening the gas valve and allowing gas to flow to the burners.

4. Igniter activation: The igniter gets powered (either a spark or hot surface ignitor) and ignites the gas, creating the flame.

*SAFETY CHECK*: The flame sensor ensures the flame is still burning, and wasn't blown out, which would pour gas into the house. Failure to 'sense' the flame, would cause the furnace to turn off. If all of the furnace's safety switches remain in the 'safe' position, it allows the next steps to happen and warm up your home.

*Main Operation*

1. Heat exchanger warms up: The heat exchanger(HX) absorbs heat from the flame, and once it reaches temperature, the board tells the blower fan to start. 2.

Blower motor activation: The blower motor begins to circulate warm air through the house via the ductwork.

*SAFETY CHECK*: The overlimit switch ensures the heat exchanger doesn't overheat. If the blower motor dies, or there's obstructions(like a plugged filter), it would trip this safety and turn off the furnace.

4. Exhaust venting: The inducer motor continues to push the exhaust gases outside through the venting system. The white pipes are called System 636. It's the only approved venting system for high efficient furnaces in Canada.

*Shutdown Sequence*

1. Thermostat satisfaction: once the temperature in the room reaches the setpoint, the thermostat removes the signal to the furnace control board, which shuts off the furnace.

2. Gas valve closure: The gas valve closes, shutting off gas supply.

3. Inducer motor shutdown: The inducer motor purges for an extra 30 seconds to a minute; ensuring all harmful gases are out of the home; and then turns off.

4. Blower motor shutdown: The blower motor runs for a bit longer(typically 1-2 minutes) to ensure all warm air is moved around the home.

That is the basics behind how a furnace works.

Join us next time when we dive into this deeper and start to discuss troubleshooting of these furnaces. 

 

Back to blog
  • Ray Richer | President

    Ray is considered one of Ottawa Valley's most knowledgeable residential HVAC specialists. With over 15 years working in the industry, he's helped thousands of homeowners with their heating and cooling systems, as well as renovations, exterior landscaping and large commercial projects.

GET IN TOUCH

  • Zone 1

    Cumberland

    Orleans

    Clarence

    Rockland

    Clarence Creek

    Navan

    Sarsfield

    Carlsbad Springs

    Vars

    Hammond

    Cheney

    Wendover

  • Zone 2

    Ottawa

    Central Ottawa

    South Keys

    Vanier

    Rockcliffe Park

    Gloucester

    Blackburn Hamlet

    Nepean

    Bells Corners

    Barrhaven

    Riverside South

    Findlay Creek

    Greely

    Metcalfe

    Russell

    Embrun

    Kenmore

    Morewood

    Forget

    Cannamore

    Marionville

    Limoges

    Chrysler

    St-Albert

    Casselman

    Saint-Isidore

    Fournier

    Plantagenet

    Alfred

    Lefaivre

    L'Orignal

    Curran

  • Zone 3

    Kanata

    Stittsville

    Dunrobin

    Carp

    Woodlawn

    Constance Bay

    Buckham's Bay

    Fitzroy Harbour

    Arnprior

    Braeside

    Pakenham

    Kinburn

    Munster

    Carleton Place

    Ashton

    Ashton Station

    Mississippi Mills

    Merrickville

    Franktown

    Kemptville

    Winchester

    Osgoode

    Kars

    North Gower

    South Gower

    Hallville

    Manotick

    Richmond

    Vernon

    Mountain

    Chesterville

    Finch

    Berwick

    Avonmore

    Moose Creek

    Dunvegan

    Vankleek Hill

    Hawkesbury

  • Zone 4

    Smith Falls

    Perth

    Lombardy

    Lanark

    Renfrew

    Burnstown

    Waba

    Calabogie

    Maxville

    Bonneville

    St. Andrews West

    Lunenburg

    Newington

    Cornwall

    Apple Hill

    Martintown

    Williamstown

    Lancaster

    Alexandria

    Summerstown

    South Mountain

    Glen Walter

    Spencerville

    Peltons Corner

    Burritts Rapids

    Long Sault

    Ingleside

    Morrisburg

    Iroquois

    Cardinal

    Johnstown

    Domville

    Prescott

    Maitland

    Oxford Station

    Oxford Mills

    Munster

    Dwyer Hill

    Prospect

    Actons Corners

    Brockville

1 of 4