Most homeowners never give their furnace a second thought other than adjusting the thermostats temperature and changing the furnace filter, but is there more to know about how the ducts in your house work? If having the cleanest possible air in your home and a substantial yearly saving, then this article might interest you.
Your furnace basically begins in the large box in your basement that contains an air handler (fan & filter), which blows air across heated coils (in winter) to heat up the rest of your home. A flue expels the combusted gas from the furnace to the outside (carbon monoxide). The carbon monoxide detectors in your home make sure there are no leaks escaping to the interior of your home. The metal duct work coming from your furnace typically has a large rectangular box running the length of your home (known as the trunkline). Duct pipes (usually round) are then run to every room in your home. If it’s a large room, it may have two registers, but often you will find them under windows where cold air is typically leaked in from (due to imperfect glass insulating properties). Once the air in any of the rooms cools down, it drops to the bottom of the room where cold air vents return it to the furnace for heating it up again and recycling the process. Blocking cold air returns can make the furnace work harder as it does not have enough return to recycle it again.
A thermostat constantly monitors the temperature of the home (typically found on the main or top floor of a home). When the temperature of the home drops to a certain level (often using an expanding/contracting metal coil to tilt a mercury switch), the thermostat sends a signal to the furnace to turn on. Once the room reaches an upper limit (typically a few degrees Fahrenheit above the set point), the furnace receives the signal to stop heating the coils, while the fan continues to blow over the already heated coils for another few minutes. The whole cycle can last anywhere from 7-20 minutes depending on how much it needs to heat.
As every home tends to have a unique floor plan, so the duct work is basically customized for each home as well (following an architect’s layout). In all homes, rooms have different square footage, and since the furnace doesn’t know this, no two rooms will have exactly the same temperature. Since hot air rises, typically the upper rooms of homes are hotter while basements are the coldest. Vents in basements are found in the ceiling and in the floors in higher floors. If the home was insulated properly this is the general rule. However, in custom and luxury homes where there is a vaulted ceiling in a great room, the heat can often be trapped at the top, making it harder to regulate that room with the rest of the house. Conversely, in rooms that have large windows facing the sun, rooms can heat up quite a lot, also impacting the regulation of your thermostat. This can be solved with smart zoning.
System Zoning to Control Temperature in Different Rooms
In most homes, there are always rooms in the home where some are colder while others are warmer. There are many reasons that can tribute to this, but one of the best ways of fixing this issue is by using system zoning. This involves multiple thermostats around the home connected to a control panel for the furnace. The control panel controls dampers within the ducts according to that room’s thermostat. This works well for family members who like different temperatures. You can also replace your existing vent registers with smart registers. The register has its own thermostat that opens and closes based on the set temperature. Either of these methods can save up to 30% on your heating bill.
Other Ways of Saving Money on Your Heating Bills
There are many things that can be done to improve the performance of your air ducts/HVAC system such as:
Taping up seams of your ducts with aluminum (or duct tape) – make sure to use aluminum tape nearer to the furnace or duct tape will eventually peel away
Use a programmable thermostat
Replacing the air filter by its recommended rating
As hair, skin cells, dust, mold, bacteria and fur are constantly being sucked in to your furnace, it is a good idea to have your ducts cleaned every 3-5 years (more often if you have pets, kids, live on a dirt road, or have family members with breathing issues) – this is a good time to get your dryer vents cleaned out as well to reduce the risk of fires
Keep the furnace are clear for best air flow
Use curtains in rooms with large windows as another insulator to the outdoor cold air
Get your furnace serviced once/year to make sure there are no leaks, it is clean and working at optimal performance. This is especially critical for oil furnaces.
Make sure all registers and cold air returns are clean of blockages (ie furniture)
Make sure there are no blockages in vent registers especially if you have small children
Reducing your thermostat by 1 degree Fahrenheit for 8 hours/day can reduce your heating bill by 1%, while reducing your thermostat by 10 degrees for 8hours/day can save you up to 10% on your heating bill
Use low-shedding carpets in rooms where appropriate
Use fans to move air around
This article would not be complete without discussing how air conditioners tie in to an existing furnace. Air conditioners come in 2 parts: an indoor air handler and an outdoor condenser unit. In an existing central air system, evaporator coils are placed in front of the furnace blower to blow the cold air coming off the coils throughout the vent systems. As the coils become warmer, freon is circulated to the outdoor condenser, where the heat is removed and recycled back to the furnace as cold liquid.
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