When you add an ADU to your home, you’ll need a strategy to heat and cool the space and to manage its air quality. Your existing HVAC system may not be able to handle the extra square feet of the ADU. In this case, or if it is detached, the ADU will need its own HVAC system to cool, heat and ventilate it as well. As this is a smaller space, and you have the opportunity to pick a system from scratch, it’s worthwhile to look into more options than just your typical furnace and central air conditioner options that most full-sized homes end up with. Here is a wider range of options you should consider.

1. Integrate into Existing HVAC System

When it’s possible, integrating your ADU into your existing space may make sense. First, you need to make sure that your current furnace and air conditioner can handle the extra square footage. Each will be rated for a certain size, and trying to heat or cool space with an undersized unit won’t work and will waste a ton of energy too. However, if your furnace and air conditioner are already oversized, then you can add air ducts in the new space and let your HVAC system handle the rest. Although, be warned that air ducts take up a lot of space and may not be the most efficient option.

2. Mini-Split Heating and Cooling

Usually, the most efficient option to heat and cool your ADU are mini-split systems. These do not need ducts but simply blow hot or cold air out from the unit itself, which sits on your wall. The combination heating and cooling units are most convenient as you only need to maintain one unit instead of two separate ones for heating and cooling. Mini-splits are highly efficient and will help keep your utility costs in the ADU low.

3. Fireplaces and Furnaces

You could also choose to use a fireplace or a furnace and pair it with another cooling option for the summer. Furnaces are a reliable option that most homeowners (and potential tenants) are used to. However, they may be too large for all but the largest ADUs. Fireplaces may work for those smaller ADUs. Gas fireplaces are most reliable and efficient and usually a cheaper option than electric or wood-burning.

4. Radiant Heating

Radiant floor heating is another possibility. It is a great option if you are repurposing a garage and need to remove and repour the flooring anyway. Radiant heating provides consistent heat, and it can be relatively efficient. You will need to find room for the boiler, though.

5. Window and Portable Air Conditioners

If you aren’t using your home’s central air conditioner or a mini-split, then your other options for cooling are window and portable air conditioners. Neither is as efficient as a mini-split, but they do have their own advantages. A window air conditioner is the most cost-effective solution in terms of upfront investment. A portable air conditioner can be moved around the ADU, cooling the space that you’re in.

It is best to get a professional’s advice from an ADU builder in Berkeley or the surrounding areas about which HVAC options would be best for your ADU.