“Conventional systems generally don’t come in sizes smaller than 1.5 tons (18,000 BTU/hr), but you can get mini-splits as small as 0.5 ton (6,000 BTU/hr), and smaller ones are coming soon.”

I have a very small bedroom in a house in New Hampshire where adding ducts would be unpractical. It would probably be well served by single-zone (1:1) ductless heat pump if I could get one in a 3,000 BTU/hr capacity. I’m concerned that a 6,000 BTU/hr unit would be oversized for a small room.

I can’t help you with the air distribution and varying temperature issue, but we’ve had a Daikin Fit, variable speed, 2 tons ASHP installed for over two years now that replaced a 2.5 tons Carrier single speed ASHP installed in late 2000. House has been improved over the years, significantly reducing load. We also have the Daikin One+ thermostat and 2 tons VS air handler. Location is southern IN, 2,160 sf, bi-level.

If you have any interest, there is a lot of information and user/dealer adjustable settings available in the One+ stat under: Settings/Dealer Edit/(enter last four digits of stat MAC address)/begin setup. From here you can change and/or view many things. I have reduced the T the aux. heat strips come on to -5F, heat pump to operate down to -10F, house preferences/data, filter reset, etc. You can also see technical data concerning pressures and temperatures at outdoor coil, indoor coil, fan speeds, etc. Since mine is new, I’ve taken some pictures of operating data to benchmark if I have problems later.

Also very interesting is ‘Quiet mode,’ which can be adjusted from either standard user or dealer edit setting in the thermostat. This is a reduced power mode for the outdoor compressor and fan designed to lower the outdoor sound level. The Fit is very quiet most of the time, but I’ve noticed a lower or deeper compressor sound in colder weather when in HP heat mode and operating at full speed (800 CFM). My wife says she doesn’t notice it. I’ve also watched the operation in typical winter conditions and it will often slowly ramp up, then go to high speed, then turn off after overshooting the set point. All refrigerant levels are correct, as per dealer one year service. The solution is ‘Quiet mode.’ It essentially makes the unit run at a lower capacity, using less energy and creating less noise, during heating mode with longer run times and no overshooting the set point. But what about COP? At least with our 2 tons unit, NEEP data suggests that app. 25F and below is the temperature at which running at lower speed in heating mode is less efficient than normal/higher speed operation. So I will turn it off during really cold days here.

Part of the sound issue I’m having, during winter, is likely due to a vibrating lineset. I need to remove some dry wall in the basement utility room ceiling and reattach the original pipe from our 1982 build. I’m sure it’s firmly attached. In addition, the installers just set the outdoor unit on a plastic pad that sits on compacted, level soil. I need to firmly attach it in some manner to help reduce vibration. I’ll probably need to use some concrete mass and rubber pads to attach the heat exchanger. Sound issues aside, I do like the idea of ‘Quiet Mode’ with the HP operating at lower capacity and reducing energy use between 25F- 55F. Funny, I found an Australian online forum (whirlpool) about Daikin HPs being too loud in heat mode from 7 years ago. Maybe the same thing? You think they would have improved it by ’20-’21 when the Fit HP came out here.

Overall, we are very happy with the Fit VSHP. The price was moderate, the warranty is 12 years parts and labor, and the efficiency (18 SEER, 10 HSPF) and comfort have improved versus the old single speed Carrier HP (13 SEER, 8.5 HSPF). We’re using one 21’x17’x5″ MERV 15 filter that lasts a year. It’s overpriced, but I was able to order one online this year and saved $25 versus the local dealer. Good Luck.

Shae, I’ve had 2 Daikin Fit variable speed inverter heat pumps installed almost 2 years ago in a 2-story house built 2008 in Atlanta GA. and find that if you use the mobile app and play with both the fan speeds and Comfort – humidity range settings, it can help you tailor settings to your house. The dealer didn’t know about these and only after living with the system can you get a feel for what’s right since there are so many variables involved. Not sure about the thermostat as I’m pretty balanced except for the kitchen getting a little cooler compared to the other rooms. It may help to use ceiling fans selectively?
In my case, one dealer correctly oversized by half ton, my lower floor unit in the basement and it works great with the higher average temps we have been experiencing country wide. The other dealer undersized my attic Daikin Fit and used the regular design temp which makes it struggle to keep the upper floor cool when it goes over 97 degrees outside, even with giant pine and maple trees providing some shade, something that is happening with more regularity as the world warms. I have open cell spray foamed the attic and put in attic and basement dehumidifiers and exhause fans after reading everything on this site but feel the design temps need to be updated to a few degrees higher.

Anyway to know the window units capacity? The nameplate may have the amp draw or wattage or possibly BTUH. Probably the two together are already a little more than a ton since the smallest units I find are around 6000 btuh. You’re medium size unit may be about the 9000btuh capacity that Milton has installed (or it could be a 11-12000btuh, I see a few of these that operate on 120v). So say you have a 9000 and 6000, you’re at 15000btuh (1.25tons). You’re not to peak weather conditions and are only able to maintain 77F, therefore I’m still thinking a 9000btuh single unit will be undersized. The passive solar design seems fairly sound, so as you mention air tightness is probably you’re major concern. Maybe with the improvements you mention you’ll be able to get by with a 1 to 1-1/2ton unit. Nothing beats having a good HVAC load calc done though to be sure.

My problem is that the house used to be mostly balanced with temperatures. With the new Daikin fit I find that the house is more lopsided then before. My living room/dining area is kind of one big room and my kitchen has 2 open doorways one to each room. During the winter that area is warmer then needs to be and during the summer its also warmer then it needs to be. The thermostat was never moved nor was the return air but I added in a whole extra trunk line and filter for the new unit. Both filters are 20×25 and I’m using honeywell filter grille filters so they are essentially 3-4″ media MERV 11 filters. Thermostat located in hallway where 3 bedrooms come together. Return filters are located at opposite end of hallway (one grille almost in the kitchen).

Does having an inverter variable speed unit make the placement of thermostat more critical? Should I have it moved? In my mind it should be moved.

There are TONS of setting on the Daikin Fit also. No sure if someone can help me there but I have no clue if my dealer set it up properly for my house or not.

I have two Sensi thermostats for the two zones in my home , and like the simplicity and overall functionality but agree that the temperature swing is too narrow and results in short cycles even at widest differential setting.

It is certainly more than we have now 🙂 Some window units that are boring a hole in my auditory cortex!
We are mid-90’s today with, bizarrely, a North wind and humidity of 60% (sounds low to me), heat index is 109. I have 1 small and 1 medium window unit on and it is 77 degrees in here. The house is passive solar and situated with the roofline on an E-W axis with the garage on the West End – deep enough eaves and arbors on the South so no direct sun comes in windows. Everything is ca. 1986 on deep clay soil so nothing is tight any longer – need windows, reseal them and doors and walls. It is daunting. I always enjoy this, thanks .

Thanks!