Home Performance Deep Dive Series

Can heat pump water heaters extend the life of your EV?

In a recent weekly room on Clubhouse, we were busting performance myths about all-electric homes.  Naturally, heat pump water heaters came up, and one of my green realtor colleagues in Phoenix, AZ asked about the ROI of the heat pump water heater I installed in my home last year.  My colleague has been electrifying her home, recently added solar panels, and her gas water heater was the last gas appliance standing. Beyond decarbonizing her home’s energy and direct operational savings by switching, there were further hidden benefits for some EV drivers.


Heat pump water heaters are well known for their insane efficiency.  Some models are 4 times more efficient than traditional water heaters, meaning they provide 4 times more heat per kWh of electricity used.  But there are several other free benefits produced by the function of the heat pump: dehumidification and cooling.  Heat pump water heaters use a heat pump to gather heat from the ambient air and move it to the water tank, in doing so they cool the ambient air. We ducted our cool exhaust from the heat pump water heater to our network closet.  Free equipment cooling! As a byproduct of moving air over the cool coils, another benefit is the air is dehumidified. As water heaters are often located in humid areas such as basements/crawlspaces, attics, or garages, the dehumidifying benefits of heat pump water heaters are an added bonus that could mean less reliance on other dehumidifiers (and further electric savings).


Heat is the enemy of batteries.  This is why most electric vehicles maintain battery temperature with liquid thermal management.  Ever heard your EV’s AC kick into high gear during hot weather, under hard driving, or when fast charging?  That is the car’s onboard thermal management system working to cool the batteries for better performance and battery health.  The Nissan Leaf is known for having battery degradation issues as it lacks any active battery thermal management.  Nissan chose to rely on passive air cooling for their battery, which has led to accelerated battery degradation in some cars in hotter locations or with frequent fast charges.  There have been well documented cases of Nissan Leafs in Phoenix losing battery capacity from the area’s hot weather. 


With this understanding of EV batteries, and the bonus benefits provided by heat pump water heaters, we have an interesting possible win-win for EV drivers considering a switch to a heat pump water heater.  My Phoenix colleague drives a Tesla Model 3, and beyond the operational savings, her interest was peaked on the water heater’s bonus feature of cooling the ambient air.  Her current gas water heater is located in the garage and her car’s thermal management often kicks on to cool the battery while parked in the garage.  Not surprising in Phoenix’s hot climate.  This led the conversation to focus on the heat pump water heater’s potential use for extending your EV’s battery life and reducing energy use to cool the battery via the car’s thermal management system. 


In warmer climates, it is almost standard to find water heaters in the home’s garage.  It’s not just warmer climates such as Arizona, Florida, and Texas, in Atlanta you’ll find many detached homes and townhomes built over the past several decades tend to locate the water heater in the garage. Whether you drive an EV or not, a cooler garage will be appreciated.  But if you drive an EV, you could have double benefits as the heat pump keeps the garage cooler requiring the car to cool its battery less, and any heat released from the battery can be used by the heat pump water heater.  With the added comfort benefits and more homeowners upgrading their garages, will a heat pump water heater become a must-have garage upgrade?  


Share your thoughts in the comments below.