Building an addition on your home is a great investment that gives you more square footage for living, changes the look and layout of your space, and increases the value of your home.
But before you even break ground, so to speak, it’s important to determine whether your current HVAC system is up to the task of heating and cooling the additional space.
Depending on the addition, you might not need to do anything to your current system. However, there are plenty of instances where your heating and cooling systems will need to be upgraded, expanded, or supplemented when you build a home addition.
This guide will go over everything related to home additions and HVAC upgrades, including things you need to consider, calculating your heating and cooling needs, how different types of additions can impact your choice, and the many options you can weigh for heating and cooling your new space.
Weigh Your Options Before You Build
We mentioned already that a home addition can require an HVAC upgrade, expansion, or supplementation, and you’ll want to decide what to do about your system before you plan, design, and build.
For example, expanding your current HVAC system will likely require adding more ductwork or new pipes and radiators, and you’ll want to work that into your building plans.
Another reason it’s important to choose the right heating and cooling option before you start is so you can budget for the project accurately. Having to buy a new furnace and air conditioner will require an additional investment that you may not have planned for.
Moreover, having a plan in place will help ensure you have all the tools and equipment you need, and the right professionals lined up to execute your project.
Start with a Professional Calculation
To make an informed choice about heating and cooling your addition, you’ll want to start with a load calculation. This will allow you to determine what size furnace/boiler and air conditioner your home will require, and whether you need to upgrade to accommodate the additional space.
It’s a good idea to have this calculation done by a professional because there are so many factors to consider, including:
- Square footage of the home with the addition
- Efficiency of your current furnace/boiler and air conditioner
- Direction your home faces
- Style and layout of the home with the addition
- Climate and humidity
- Number of exterior walls
- Thickness of your insulation
- Number of windows, doors, and skylights in the house (with the addition)
- Age and efficiency of your windows, doors, and ductwork
- Total heat sources in your home (such as gas fireplaces)
Options for Heating and Cooling Your Addition
The load calculation will tell you:
- Whether your current HVAC system is sufficient to handle the heating and cooling needs of your home with the addition OR
- Whether you need to upgrade your furnace/boiler and air conditioner OR…
- Whether you need to supplement your existing system
Expanding Your Current HVAC System
When your current furnace or boiler and air conditioner are sufficient to heat and cool your home as well as the additional space, then you will likely be able to expand your current system without having to purchase new units.
If you have forced air, then expanding your current system will involve building new ductwork and air supplies throughout the addition and connecting it all to your existing ductwork.
If you have a boiler system, then you’ll need to install new pipes and radiators throughout the addition and connect it all to your existing pipe network.
Upgrading Your HVAC System
Depending on the size of your addition, it’s possible that your current heating and cooling systems won’t have a large enough capacity to accommodate the new space. This is especially the case if your new addition is large or has many windows or other features that may increase heating & cooling demands.
In that case, one option is upgrading to a larger furnace or boiler and larger air conditioner with higher BTU outputs.
There are many benefits to upgrading your old furnace or A/C, especially if your current heating and cooling units are 10 years or older, are starting to break down more often, or are less efficient than the models currently available.
Upgrading will require an additional investment, but buying a brand new high-efficiency furnace and air conditioner comes with a number of advantages, including better performance, lower energy bills, convenient control systems, quieter operation, and a new warranty.
Moreover, upgrading your heating and cooling systems will guarantee that your furnace and air conditioner are sized properly for your new space, and that alone can be worth the investment (more on that later).
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Installing a Separate and Independent System
If your current HVAC system isn’t large enough to accommodate your additional space, then there is an alternative to upgrading your furnace and air conditioner: you can supplement them with additional units.
There are several circumstances when this might be appropriate, including when:
- Your existing furnace and air conditioner are relatively new
- The addition is creating a lot of extra space (such as an in-law suite)
- The addition is a separate structure from your home
- You don’t want to expand your ductwork or hot water piping
- The new space has different heating and cooling needs from the rest of the house
- The new space won’t be used regularly
- You don’t have central heating and air conditioning that can be expanded
Depending on the situation, there are several options for heating and cooling your addition with an independent HVAC system. Options include:
- Ductless mini-split air conditioners
- Ductless heat pumps (models that do heating AND air conditioning)
- Gas fireplaces or wood stoves
- Ceiling fans
- Separate furnace/boiler and air conditioner
- Window or portable air conditioners
The Type of Home Addition Can Help You Choose the Right HVAC Setup
The HVAC system that’s going to work for your renovated home depends on more than just added square footage. There are lots of reasons why the type of addition can impact what you do with your HVAC system. Here are some things to consider:
- If the addition has different cooling/heating needs from the rest of the house (such as a sunroom, library, or room above a garage), then you might want to install a separate system that’s independent from your main HVAC setup.
- If the addition won’t be used regularly, such as a guest suite, or isn’t part of your main home, then an independent system might be preferable.
- If you’re adding a small space, such as a bump-out for a bathroom or a dormer in the attic, then you may not have to make any changes to your heating and cooling systems, but you might have to add ventilation.
- If you’re adding a story to your home, then you’ll likely need to upgrade your furnace/boiler and air conditioner, or install independent units to heat and cool the space separately
- If you’re enlarging your space (such as by converting a garage) or adding a new room to an existing floor, then you might have to upgrade to larger units, or supplement the space with additional heating and cooling sources.
Upgrading Your Heating and Cooling Systems for Improved Efficiency
Upgrading your furnace or air conditioner isn’t always just about getting the right size. You might also want to upgrade your furnace and/or upgrade your air conditioner because they are older, needing frequent repairs, less efficient or effective, costing too much to operate, no longer under warranty, or not as sophisticated as the models available today.
Improved Efficiency and Performance
Consider this: if your furnace is more than 15 years old, then it might only be 70 percent efficient (and possibly less). If you want that same low-efficiency furnace to heat your home with the addition, then your energy consumption and bills are going to skyrocket (the same goes for an older and low-efficiency air conditioner).
By upgrading, you can get a furnace that’s upwards of 99 percent efficient, a boiler with an AFUE of 95 percent or higher, and an air conditioner with a high-efficiency SEER rating of 16 or more.
All of this translates to better performance, less maintenance, reduced energy consumption, and lower energy bills. Although you might have to invest more upfront, you will save more in the long run with cheaper heating and cooling costs.
Furthermore, you might be able to combine all the expenses for the project—including the cost of the new air conditioner, new furnace, and the addition—into a single low-interest loan, depending on how you’re financing the project. This will save you from having to secure a separate loan down the road for new HVAC equipment.
Finally, always choose models that are backed by great warranties, because a good warranty can save you plenty on maintenance and service calls, and will give you a good idea of how long the unit will operate reliably and efficiently.
Why Furnace and Air Conditioner Sizing Is Important
Size might not seem like a crucial factor when you’re picking out new HVAC equipment, but there are several reasons why you need to consider it.
Our furnace size & BTU calculator can help provide a basic assessment of the heating output of furnace needed by home size.
Here’s what happens when your furnace and air conditioner are oversized or undersized versus properly sized:
|Too Big||Irregular cycling, hot and cold spots, poor efficiency, increased maintenance, and a shorter lifespan||Short cycling, higher humidity levels, more maintenance, poor efficiency, and a shorter lifespan|
|Too Small||Continuous operation, poor efficiency, home is always too cold, high energy bills, increased maintenance, and a shorter lifespan||Continuous operation, poor efficiency, home is always too hot, poor humidity control, high energy bills, increased maintenance, and a shorter lifespan|
|Just Right||Regular operation, home is the right temperature, no hot and cold spots, reduced maintenance, better efficiency, good humidity levels, lower energy bills, and a longer lifespan||Proper operation, improved efficiency, right humidity levels, even temperature throughout the house, lower maintenance requirements, lower energy bills, and a longer lifespan|
How is furnace/boiler efficiency measured?
The efficiency of heating systems is measured with annual fuel utilization efficiency (AFUE). This measures the amount of fuel the furnace or boiler consumes versus how much heat it produces. The higher the AFUE, the more efficient the model.
How is air conditioner efficiency measured?
The efficiency of air conditioners is measured with seasonal energy efficiency ratio (SEER). This measures the amount of fuel the air conditioner consumes versus how much cooling it produces. The higher the SEER, the more efficient the model.
Canadian summers don’t typically require the ultra-high SEER models that are available, and somewhere between 16 and 18 SEER is usually sufficient for our summers.
How are furnaces and air conditioners sized?
The size of a furnace or boiler is measured with British thermal units (BTUs). One BTU is equal to the amount of energy required to increase 1 pound of water by 1 F. A 40,000 BTU furnace, for example, produces 40,000 BTUs of heat per hour.
Air conditioners are measured in tons, which correspond to BTUs. A 1.5-ton air conditioner produces 18,000 BTUs of cooling per hour. For each half-ton you add, you increase the BTUs by 6,000. For example, a 2-ton air conditioner produces 24,000 BTUs of cooling per hour.
How can I calculate what size furnace and air conditioner I need?
There are lots of factors that go into properly sizing a heating or cooling system, and it’s a good idea to have this done by a professional. But here are some rules of thumb so you can get a ballpark estimate of what size range to look at:
Furnaces: Between 30 and 60 BTUs per square foot.
Boilers: Around 50 BTUs per square foot.
Air conditioners: Around 20 BTUs per square foot.