(707) 800-6287 |  Sonoma Napa and Marin Counties

Edited March 16, 2022


Considering installing an HVAC in the attic? Learn all the pros and cons below.


When installing a new HVAC system in your home, one of the most important questions to consider is where to place the furnace and/or the air conditioning unit itself. These units can be pretty big and bulky, so it’s important to plan before anything is set up. Basements are often ideal locations for furnaces and air conditioners because they’re spacious, well insulated, and other units like hot water heaters and fuse boxes are typically placed down there as well. However, many homes out in California don’t have basements, which means finding a different location for your HVAC units.


While some builders west of the Mississippi create ground-floor closets and other small spaces for hot water heaters and HVAC units, you can also consider placing your furnace or air conditioner up in the attic if you have one. This can provide a number of benefits, including convenience and comfort on the ground floor. However, an attic-based HVAC system also comes with its own set of challenges and common issues. Whether you’re installing a new HVAC system or just considering moving your current units up into the attic, it’s important to understand all the pros and cons of an attic-based setup.


In this post, we’ll go over a few things to consider before installing a furnace or air conditioner in your attic, including benefits, downsides, and a few factors specific to your home that could end up affecting your decision.


Thermal Envelopes

Before deciding if you want to install an HVAC system in your attic, you should first consider the specifics of your home’s thermal envelope. “Thermal envelope” is a term commonly used in the HVAC and construction industries to refer to the insulation and sealing of your house. Essentially, the thermal envelope is anything that protects the inside of your home from the air outside. This can include the walls, the roof, any insulation in the walls, windows, caulking and weatherstripping, and even the foundation. Ideally, your house should be a tightly-sealed envelope protecting you and your family from everything outside and allowing you to control the temperature and air quality inside.


The thermal envelope is also sometimes referred to as the heat flow control layer. That’s because the most important function of the envelope is to keep firm control of the heat transfer between the inside of your house and the outside. When you were a kid, did your parents ever yell at you to keep the door closed when the A/C was on because they’re “not paying to cool the outdoors?” They did that because any break in the thermal envelope, like an open door, will cause a transfer of heat between the inside and the outside of your house. In the summer, cold air-conditioned air will leak outside while heat comes in, and during the winter, furnace-warmed air will escape and allow cold air to leak in. This doesn’t just apply to open doors or windows. Any small crack or break in the thermal envelope will allow temperature-controlled air to escape, reducing the efficiency of your HVAC system.


So what does this mean for you and your attic? Often, an attic will be the weakest part of your home’s thermal envelope. If you go up to the attic and feel a draft, or if the temperature just feels different from the downstairs, there’s a good chance that the attic has a looser thermal envelope than the rest of your house. If that’s the case, putting your HVAC units up there will make them significantly less efficient. We’d recommend either placing the units elsewhere in your home or hiring a contractor to seal the attic more tightly.


Pros of HVAC in the Attic

If you do have a suitably tight thermal envelope in your attic, there are plenty of reasons why putting the HVAC units up there could be a good idea, especially if you don’t have a basement to hide it in. Here are a few of the benefits of sticking your furnace or air conditioner up in the attic:


Noise Reduction

This benefit is less of a practical concern and more of a quality of life thing. Despite a ton of advancements in HVAC technology over the past few decades, one issue they haven’t been able to fix yet is the noise problem. Furnaces and air conditioners make a ton of noise when they’re running, which can be a real pain when you’re trying to focus on something.


Worse still, air conditioners can sometimes make noises loud enough to risk damage to your hearing. A/C units can create sounds between 80 and 90 decibels, and the risk of hearing loss starts around 70 decibels or so. Does that mean your air conditioner is going to make you lose your hearing? Almost definitely not. But prolonged exposure to sounds over 70 decibels creates a risk, and even the smallest risk is worth avoiding.


By placing your air conditioner or furnace up in the attic, you can drastically reduce the amount of noise you hear downstairs while the system is running. This is a little more convenient, especially if loud noises make it difficult for you to sleep. While this particular factor won’t affect the function of your HVAC system, it’s still worth considering, especially if you’re sick and tired of the sound of your air conditioner running every day.


Protection From Water Damage

If you live somewhere subtropical like the coast of the Gulf of Mexico, this is probably the first benefit that you thought of when you considered moving your HVAC system to the attic. Anyone living in that area knows firsthand the inconvenience of a flooded basement, whether that’s from a hurricane or just your standard torrential downpour. Any time your house is flooded from the outside, the lowest floors will always be the first to be filled with water. That means anything in your basement is at risk of being damaged by rainwater, including your HVAC system. Placing the furnace or air conditioner in the attic reduces that risk significantly. After all, if the flooding is so bad that it even reaches your attic, then you probably have much more serious problems than a damaged air conditioner.


Even if you live in the middle of the Mojave Desert, your home can still be flooded. Despite being safe from the threat of hurricanes or heavy rain, internal problems like a broken pipe can flood your house with the water from your plumbing system. Placing important units like the furnace or air conditioner in the attic will protect them from this kind of flooding as well. When a pipe breaks, it’s always the floors below that are affected by the water. Because there’s really no reason to have water pipes running through your roof above the attic, there’s essentially zero risk of a broken pipe flooding your HVAC system up there.


Shorter Ducts

If you have a standard ducted HVAC system, placing the heating and cooling units in the attic will reduce the length of the ducts required to transfer air throughout the house. Because vents are best placed in the ceiling or high on the walls, an HVAC system based in the basement will require enough ductwork to run all the way up the walls in the basement as well as the walls and ceilings of every floor above it. If you place the units in the attic, however, the ducts have a short path directly down into the floor underneath, and you’ll only have to run ducts through your walls if your home has multiple levels.


This is beneficial for a few different reasons. The first is pretty straightforward: cost. Shorter ducts require fewer materials and can be installed faster, which saves you a little money when you’re putting them in. They’re also quicker to maintain and clean.


Shorter ducts will also save you money by making your system more energy-efficient. One of the most common ways for an HVAC system to lose efficiency is through air escaping small breaks in the ducts. If temperature-controlled air is being lost in the ducts, the system has to work harder to replace that air, which raises your electricity bill at the end of the month. Shorter ducts, however, offer fewer opportunities for the air to escape. This can make your system run much more efficiently, saving you some cash every month.


More Space in the Home

This is another quality of life advantage rather than one that affects the actual function of your HVAC system. Simply put, HVAC units can be kind of an eyesore. They’re big, boxy, and they take up a ton of space that can be used for something else. If you place your air conditioner and furnace in the attic, you’re saving yourself at least a closet that can be filled with something more relevant to your day-to-day life. This is especially true if your home doesn’t have a basement, so you’d otherwise be forced to find space for your HVAC system somewhere else in your living space.


Fewer Pests

This advantage can vary depending on where you live, but the pests found in a basement can sometimes be worse than the ones in your attic. Bugs, spiders, and other creepy-crawlies typically prefer darker, cooler areas like basements, so putting the HVAC system up in the attic can protect it from those little critters. However, your mileage may vary on this one, since some pests like squirrels and birds are more commonly found in attics. The preferred hangout spots of your local pests are something to consider when deciding where to place your HVAC units. If you like, you can ask your HVAC installation company for their recommendation. They’ll typically know the area pretty well, and can let you know if the units will be safer up in the attic or down in the basement.


Cons of HVAC in the Attic

Of course, everything has both pros and cons, and attic-based HVAC systems are no exception. While there are advantages, putting your HVAC units up in the attic comes with its own set of particular challenges. Here are a few things to consider before you move your HVAC system upstairs:


Harder to Maintain

Keeping an HVAC system up and running smoothly takes regular maintenance, which can be difficult in the attic for a few different reasons. First, having your air conditioner in the attic can lead to an “out of sight, out of mind” mindset. When you’re not seeing and hearing your HVAC units every day, it can be harder to remember to keep up with regular maintenance like swapping out the filters and cleaning the units. This can lead to bigger and more expensive problems down the road.


With HVAC units in the attic, it can also be harder to detect potential problems within the system. Sound is often one of the easiest ways to tell if something is wrong – hearing anything other than the standard air conditioner humming is a good sign that something is broken. Sometimes these symptoms are apparent before the actual function of the unit is affected, and the sooner you address them, the less expensive the whole thing will be. If you can’t hear the system running, however, you can miss signs of problems until they start to affect the actual airflow. At that point, you’re already looking at potentially high repair costs.


Uninsulated Ducts are Inefficient

It’s not uncommon to go up to the attic and see bare ducts running every which way. This is convenient for cleaning and installation, but a lack of insulation can cause problems for your system. If the ducts are exposed, then the air inside them is also being exposed to the ambient temperature inside the attic. That means heated air will cool down, and cooled air will get warmer. By the time the air reaches your vents, it’s not even the same temperature that it was when it left the unit. This forces the whole system to work harder and make up for all the lost energy inside the attic, potentially leading to higher electricity bills.


The way to avoid this is by making sure your ducts are insulated, no matter where they are. That can mean placing them in the floor or crawl space under your attic if there’s room, or even just having insulation placed around them when they’re installed. Insulation is extremely important, so wherever you choose to have your HVAC system set up, make sure your ducts are properly insulated all throughout the house. Otherwise, you could end up losing energy every time the system turns on.



Some attics are spacious and easily accessible, but many of us have attics that are small, cramped, and hard to even get to. That can obviously present an issue when it comes to maintaining your HVAC system. As a general rule, we recommend having your system services by an HVAC technician about once a year. The technician will make sure everything is running smoothly, check on the refrigerant levels in your air conditioner, and clean a few things that can get clogged. It’s also recommended to have your ducts fully cleaned every three to five years.


Having all these things in the attic can make it difficult for the HVAC tech to get in there and do the necessary maintenance. The same goes for the maintenance you can do by yourself. It’s harder to get up there and change the air filters every month if your attic is cramped. If you do install your HVAC system in the attic, we recommend cleaning it up a little and making sure there’s a clear path to both the duct access points and the units themselves. This will save you a ton of hassle every time your units need to be serviced.


Air Leaking Into the Attic

As we mentioned before, there’s always the risk of air leaking from the ducts while the HVAC system is running. This obviously creates a problem for the efficiency of the system, but it can also cause issues for your attic as well. Temperature-controlled air can be fairly moist, and if it escapes through the ducts, it can create an unpleasantly humid environment in the attic itself. This is especially true if your air conditioner or furnace doesn’t have proper ventilation to the outside.


Not only does this humid air make the attic unpleasant to be in, but it can also start to cause problems with rot or mold. Since attics are often full of exposed wood beams and walls, excess moisture in the air can cause that wood to rot or even form mold. Insulating the ducts can help with this problem, and so can carefully maintaining the ducts themselves to make sure no breaks or holes appear where air can escape. This will help protect any exposed wooden structures in your attic as well as maintain the energy efficiency of your HVAC system.



Furnaces and air conditioners both create a ton of condensation as they either heat or cool the air. Typically, that condensation is collected in a pan under the unit and flows through a drain line to the outside, so it’s not a problem. However, sometimes the lines can become clogged, causing water to build up in the drain pan and overflow. The pan itself can also be damaged or cracked, allowing some water to escape and drip down under the unit.


In a basement, this isn’t a huge problem. A little water will pool underneath the unit until you finally discover it and fix whatever is causing the leak. However, if your HVAC units are up in the attic, that water won’t just collect under the unit. A leaky or overflowing drain pan will cause water to drip down from the attic into the ceiling of your living area, potentially creating water damage. If you do decide to install your system in the attic, you should make a note of which room is directly underneath the units. Keep an eye on the ceiling under the HVAC system. If you see water dripping down from above, you probably have a clogged drain line or similar problem.


Figuring Out if Having an HVAC in the Attic is Best for You

Ultimately, the best place to put your HVAC units will depend on your individual home, situation, and preferences. As a general rule, we recommend the basement for people who have one, but since many houses in California don’t have them, an attic is a great replacement. If you can make sure the units are accessible and the ducts are well-insulated and sealed, it’s probably worth it to get the whole system out of the living area and give you and your family a little more space downstairs. However, this will obviously depend on your own preferences and home, so think about it before you make a decision.


Wherever you decide to install your HVAC system, you should make sure to hire a professional HVAC installation company. This is absolutely not a good DIY project, and even small mistakes can lead to huge electricity bills or costly repairs later on down the road. Your local HVAC professionals will also be able to help you figure out where to place the units by taking a look at your home and giving you some advice. Remember that these people often have years or even decades of experience in this area, so take advantage of their knowledge!


If you’re in Sonoma, Napa, or Marin Counties and you’re interested in moving your HVAC system upstairs or installing a new one, or you just have more questions, feel free to give Valley Comfort Heating and Air a call at (707) 644-7201, or get in touch with us through our website. We have all the experience you need to find the perfect location for your HVAC units, and we can install them for you too. If you’re ready to change up your HVAC system, a better solution is just a phone call away.