Author: Wei-Tai Kwok, Past President, Sustainable Lafayette
As mentioned in my earlier blog-post, my wife and I went to a highly informative presentation in Berkeley, CA in February 2019 where the workshop leader, Sean Armstrong, explained and completely demystified the roadmap of how we could achieve a zero carbon home. (Watch Sean’s workshop video and download his PPT presentation)
I’m going to focus this blog post on how we upgraded our ducted gas furnace and central air conditioning system to an electric heat-pump mini-split heating and cooling system.
We have a 2-story split-level home located in the suburbs of San Francisco, CA. How do we currently heat and cool it? For upstairs, there is one furnace and A/C unit perched in the attic and attached to a maze of ducts and ceiling vents. Downstairs, a similar furnace and A/C bring heating and cooling via ducts suspended in the crawlspace under the house and surfacing via floor vents.
An air-source heat pump makes good economic sense for heating and cooling our Northern California home, because we have a mild climate. Heat pumps work most efficiently when the average temperature is warmer than 50°F degrees, and usually no lower than 25-30°F, which we never see in the SF Bay Area. I had looked into heat pumps in 2003 when we were constructing our home, but at the time the common technology was ground-source (or geothermal) heat pumps (which extract heat from a maze of pipes buried at least 5’ underground to absorb the constant 50°F temperatures prevailing at that depth).
My builder didn’t know much about heat pumps, and my go-to-resource for answering all questions, YouTube, hadn’t yet been founded (it launched Feb 2005). Good thing I didn’t go with a heat pump then, because modern air-source heat pumps have advanced so much in the meantime (thanks to China, which we’ll talk about below) that now is actually a perfect time to get one installed.
Anyhow, back to the zero carbon home expert, Sean Armstrong, who explained two main approaches to replacing our gas furnace with heat-pump electric.
1. Keep all my ducts and vents, and just replace the central gas furnace with a heat-pump electric. I immediately liked this approach, as it sounded so straight-forward. To my surprise, though, Sean did not recommend this approach. Instead, he preferred to abandon the existing big 6”-8” diameter ducts and vents and to replace them with 3-4” ducts more efficient with heat-pumps. In fact, while you could go thru the trouble of running these new 3” vents inside the existing 6” vent work, he actually recommended uninstalling and removing the old ones totally.
Why? Because legacy HVAC systems are (poorly) designed to blow very hot air, super hard, for short periods of time. In contrast, the new heat pump systems (smartly) blow warm air, with mild force, but for longer periods of time. (Compare the energy it takes to blow water out of your mouth through a 5’ plastic straw, slowly through a thin one, or quickly via a thick straw…the thick one would take a lot of energy and force, while with the thin one only moderate force is needed).
Anyhow, the net takeaway was that keeping my ducts for my retrofit was not the top approach. My project looked like it was about to get more complicated!
2. Mini-Split Non-Ducted Solutions: Sean reviewed another approach which he said was very common now in Asia, which is to have a central heat pump compressor unit outdoors feeding up to five “mini-split” air handlers installed indoors. There are no ducts in this design, just electrical cables and refrigerant lines.
A huge light went off in my head when he said “hundreds of millions of people in China, Japan and the rest of Asia for that matter use heat pump mini-splits to heat and cool their homes.” I’ve seen and used them countless times during my Asia travels, what with each room having a remote control and the ability to adjust the fan levels. It didn’t’ really register in my head that the reason was because it’s simply the most cost-effective way for them to get modern day comfort and that someday my house would benefit from this same technology.
The great news is that the rapid growth in Asian demand has driven manufacturing costs down and quality and innovation up. Americans can now benefit from Asia’s past decade of rapid product advancement.
I heaved a sigh of relief that his recommended solution was something I was already familiar with, albeit unconsciously. Going with heat-pumps was not something expensive, exotic and risky.
WHAT WE WENT WITH
If you’ve read my previous three blog posts, you’ll know the rationale of why I hired a single contractor to propose a system-approach to all my energy efficiency and building electrification upgrades, rather than a point-by-point approach using different subcontractors. I didn’t want to be at this juncture of having a little bit of Sean’s information, and then shop HVAC contractors who were more likely to propose “what they’re used to selling” (e.g. ducted or non-ducted system, or even trying to talk me out of a heat pump) rather than what might be right for the energy profile of my house. After conducting an energy audit of my home, my contractor recommended a Fujitsu Halcyon Mini-Split (non-ducted) solution. What did this entail?
DESIGN AND INSTALLATION
There are a couple of issues I think readers should know as they contemplate mini-splits.
1. Placement of the indoor mini-split air handlers
There are a several choices of air handlers which can be placed on the wall, in the ceiling, on the floor, etc. Each has different pros/cons in terms of aesthetics, installation and function. What you do depends on your home design, your interior design choices, etc. My wife Violet initially didn’t like the idea of wall-mounted units: “Are we really going to hang those big ugly things in every room?” At 32” wide and just 8” deep and 10” tall, I didn’t actually think the white plastic units looked all that big and ugly. We asked our contractor about more discrete options like the “cassette” style which could be installed flush into the ceiling.
Our contractor said those were possible, but if comfort was a higher priority, the wall mounted units would circulate the air better and the result would be superior room comfort. The ceiling cassettes would be more invisible, but the trade off is their lesser ability to mix the air. Violet and I felt room comfort was a higher priority, and so we proceeded with eight wall mounted units (4 upstairs, 4 downstairs). And the good news is that after installation, Violet now thinks “they are not that bad looking after all, and you don’t really notice them after a while.” Whew, said the husband.
Also, each mini-split should ideally be installed on an exterior wall, so that the condensation created during the A/C process can be gravity-drained away. We were able to do this for 6 of our 8 mini-splits, but for two of them we located them on an inside-wall and needed to install a mechanical pump to push the condensate water upwards into the attic, then over to a downspout. Not the end of the world, but such pumps will eventually need servicing.
Here are photos of what the wall units looked like after installation in our home. Is it ugly? Or OK?
Note that each one is operated by its own remote control. All remotes are interchangeable, meaning any remote can control any unit…just get close enough and they work.
2. Placement of the outside compressor units
Our eight indoor units needed to be paired with two outdoor units. After mounting each wall unit, the contractor drilled a 3” hole through the wall to allow for tubes and cables to run down to the outdoor unit.
The aesthetics of that outdoor equipment pad and the connections, however, was where my wife and I grimaced the most. This wasn’t going to make our home look better, only worse, but just how much worse was the question. I’ll leave that to you the reader to judge how good or bad the outside looks before and after. Most of the websites and industry vendors will tell you “it looks just like a gutter” and after painting it to match our home, it probably will not be that noticeable. But for us it was one of the compromises we had to make to “go electric” in a sensible way. For those luckily enough to install heat-pumps during new construction, the line sets can be hidden in the walls.
Aside for how the units looked, another concern I read about was noise levels, so I read up on that. But it turns out heat pump fans are much quieter than the powerful A/C compressor fans I was replacing, which blew with airplane force. My new outdoor units are as quiet as my laptop fan…basically noise is a non-issue. And indoors, the units run quietly as well. Don’t worry about it.
WHAT DID I DO WITH MY OLD FURNACE AND A/C?
I cringe at throwing usable items into landfill, and since my existing system was only 15 years old with light use, I actually listed everything on CraigsList and Facebook Marketplace and managed to sell everything piecemeal for a couple hundred dollars (Note the AC condenser units are worth the most! Furnaces were harder to sell).
Also, my old ductwork and vents all got removed during this process, so there was drywall patching, sanding and painting involved here. That meant covering up a lot of the house in plastic.
COSTS & SCHEDULE
The cost for system design (performing a Manual J heating and cooling load calculation and a Manual S equipment selection calculation), removal of existing furnace and duct system, drywall patching, Fujitsu equipment, parts and installation was approximately $25,000. Took about 10 working days to complete.
So how comfortable is our home, now that we’ve had this new system for the hot month of August? We’ve definitely enjoyed turning on the AC mini-splits in each room that we’re in, knowing that’s more energy-efficient than cooling our entire upstairs like we did in the past. The cool-down times were actually pretty quick…maybe 10-15 minutes to get comfortable and 30 min to get downright cold if we wanted. We were impressed by the strong air handling capability despite these being smaller than 32” x 8” x 10”. The units run very quietly indoor and out.
We seldom used our old A/C and were somewhat embarrassed when family and guests came on hot summer days because our system simply didn’t cool the home down very much. I learned through this process that while my old AC was oversized and properly maintained, the ducts were designed and installed poorly, such that the cool air warmed significantly before entering our home.
I will have to add on to this blog when winter comes to report back on how these heat pump systems work in heating mode.
In the meantime, stay tuned for my next blog entry where we continue our summer journey to remove fossil fuels from our home. I’ll talk about replacing our gas domestic water heater with heat pump electric: this retrofit surprisingly involved the hardest decisions, so stay tuned to see why.
2 Outdoor Units: Model AOU36RLXFZ1 (36,000 BTU, 18 SEER, 9.4HSPF)
8 Indoor Wall Units: Model ASU9RLF1 and ASU7RLF1
Installer: Eco Performance Builders, Concord, CA.