Size Your System


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When it’s cold outside, you expect dependable and efficient heat. If your old heating system has seen better days and it’s time to buy a new gas furnace, there’s no law saying you have to purchase a new one from your installer. When you get a residential furnace online at HVACDirect.com, you can save thousands of dollars. Then you simply have a certified professional install it for you.

Online shopping lets you choose from the convenience of your home or business. None of our employees work on commission, so you’ll encounter no high-pressure sales tactics here. Long into the future, a new gas furnace will compound your savings, bill after bill.

We carry a sizable selection of heating furnaces from leading brands you can trust, like Goodman Furnaces and AirQuest By Carrier Furnaces. You can find just the right replacement furnace or heating system to suit your home and budget. When you buy a furnace online, you can enjoy significant savings — especially when you choose from our inventory of High-Efficiency Furnaces.

Each of our high-efficiency natural gas furnaces is available with a liquid propane conversion kit. Shop our selection of brand-name furnaces and use the shop-by filters at left to choose your furnace efficiency, BTUs and other custom features. To learn more about the options you need to consider when you purchase a furnace online, including blower motor speed and burner stages, watch the videos linked to each filter.

Frequently Asked Questions

When should you replace Your furnace?

You might want to Replace Your Furnace for several reasons. Most often, a furnace no longer functions properly. It may be blowing cold air, leaking an excessive amount of water or not heating your home sufficiently because of a house upgrade, renovation or expansion. Worse yet, the furnace may not work at all.

New gas furnace prices will seem like a bargain when you consider the heating costs caused by outdated systems. Older furnaces have inefficient blower motors and even less efficient AFUE, which stands for their annual fuel utilization efficiency rating. If your bills are larger than your heat output, it may be time to upgrade your furnace. Regardless of when and how you want to replace your furnace, consider the cost of the new equipment and the efficiency of the furnace and what that will save you in the long term.

What is furnace capacity?

Furnace Capacity refers to the maximum heat output of a furnace, measured in BTUs (British Thermal Units). The higher the BTUs, the more heat. Most homes will have a furnace with a capacity of 60,000 – 100,000 BTUs. Several factors determine the ideal size of furnace, with house size and its geographic location being the two primary factors.

How often should you have your furnace serviced?

You should have your furnace serviced once a year when the unit is in prime condition, more often when it starts showing signs of aging. The best time to service a furnace is prior to the beginning of heating season.

Routine servicing of a furnace ensures it performs at peak output with minimal effort. Furnaces that fight against themselves, attempting to push air through blocked or occluded airways, generating heat with nowhere to go and struggling with dirt and grunge on their moving parts use more energy and usually succumb to failure way before their time. Failure to service a furnace generally results in higher energy bills, increases the risk of fire or carbon monoxide poisoning and voids the warranty for virtually all brands of equipment.

How do you calculate furnace size?

You calculate furnace size by multiplying the square footage of the house by the heating factor – a value based on climate factors expressed in BTUs. For example, a 2,000 square foot house in a region that has a heating factor of 30 (mild winters) would require a unit with a heating capacity of 60,000 BTUs. To make this a little easier, we’ve developed an HVAC System Sizing Guide to help you determine the size system and options you need for your climate and conditions.

There are other factors to consider and account for, including insulation, age of the house, ceiling height and doors and windows. These might not require a major adjustment but should not be overlooked. Ceiling height is particularly noteworthy. Experts recommend increasing your BTUs by 25% if your home has vaulted ceilings throughout. (The standard ceiling height is eight feet. Few homes have ceiling heights that consistently exceed eight feet. Perhaps one room – a dining room or formal living room - would have a vaulted ceiling, but the other rooms would likely have standard ceiling heights.)

With furnaces, bigger is not necessarily better. First off, the more BTUs a furnace produces, the greater its initial cost, and the more energy it will use while it is running. Secondly, the runtime of an over-sized unit will be shorter, and may not allow for sufficient dehumidification.

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