Ductless Mini Split vs Conventional Furnace / AC

[DETRoadster]

As some of you know, I'm in the process of having a house designed and built (Approx. 1800 to 2000 sqft). Our architect is really pushing the whole space-age technology of a ductless mini split HVAC system. I understand how they work and for a retrofit in an existing home can see the benefit. I'm just not sold on their value in new construction over a well-designed ducted system.

- I hate the look of the air handlers but understand there are some that can be built into the wall or ceiling.

- They seem complex (ie, maintenance and repair issues down the road). All the expansion valves, plumbing refrigerant all over the house under pressure, lots of filters that need cleaning/replacing.

- Still not convinced that just 4 or 5 air handlers can adequately heat/cool all the rooms. Especially because we tend to close doors to rooms we arent actively using to keep the dogs out.

- Electricity in the PNW is cheap, but so is natural gas. Not seeing a real cost benefit.

Anyone with experience with one of these systems in new construction who can comment and convince me it's better than a high efficiency ducted furnace and AC system?

[2000cs]

I recall that they are common in Japan, but I don’t recall seeing them used for every room in a house. I share your concern about the hardware scattered throughout the house - would want everything except the plumbing to be accessible.

I also would think about condensation on the lines, dripping in the walls. The piping ought to be properly wrapped/insulated to prevent this.

I guess this requires less room (tubing vs ducting) in the house, so is cheaper to install. No ducts to clean is a plus. Fan noise in each room could be a negative.

I’m open to new ideas and approaches, but I’d want to see a comparable installation and warranty.

While nat gas is currently inexpensive, it is the next fuel under attack for its contribution to climate change (after coal, nearly dead). Expect the price to go up as supplies are constrained and carbon tax of some sort is implemented during the life of your house.

That’s all I’ve got.

[Frostynorth]

Ductless splits are nice, super quiet. Sounds as you want a full forced air system though.

An existing building ductless requires a lot less work, they are reliable, but replacement parts are expensive.

A setup with four of five heads could cool down those rooms, and be less expensive to run when rooms are unoccupied.

I've installed both (except running ductwork) and each has their benefits.

Many ductless are heatpump setups so they can cool and heat.

If I were building a house would just go forced air. They're overall simpler to service, easy maintenance (change filter, clean condenser, and get the gas heat checked once in a while - though I never check mine). Parts are much cheaper to replace as there are no complicated boards or electronics.

If it was just a room or two, or running duct is complicating the design of the house, ductless splits are pretty cool. If they're properly installed, there should be no major issues.

-

Where I live, natural gas/LP heating is pretty much required, as it's much cheaper to operate than electric. Gas furnaces are getting 96% efficiency. Ductless heatpumps can't generate enough heat when it's -30, they're good to about -10c. Still wouldn't bother.

I've spent hours trying to resolve ductless problems when they arise, it's ended up being boards (there are multiple) or compressors. The electronic expansion valves have been reliable.

[DETRoadster]

Originally Posted by 2000cs

I also would think about condensation on the lines, dripping in the walls. The piping ought to be properly wrapped/insulated to prevent this.

Exactly! There's just so many ways the system could go wrong. I dont want to find out 20 years from now I've got the aluminum wiring or T-111 siding of HVAC systems.

[DETRoadster]

Originally Posted by Frostynorth

Ductless splits are nice, super quiet. Sounds as you want a full forced air system though.

An existing building ductless requires a lot less work, they are reliable, but replacement parts are expensive.

A setup with four of five heads could cool down those rooms, and be less expensive to run when rooms are unoccupied.

I've installed both (except running ductwork) and each has their benefits.

Many ductless are heatpump setups so they can cool and heat.

If I were building a house would just go forced air. They're overall simpler to service, easy maintenance (change filter, clean condenser, and get the gas heat checked once in a while - though I never check mine). Parts are much cheaper to replace as there are no complicated boards or electronics.

If it was just a room or two, or running duct is complicating the design of the house, ductless splits are pretty cool. If they're properly installed, there should be no major issues.

-

Where I live, natural gas/LP heating is pretty much required, as it's much cheaper to operate than electric. Gas furnaces are getting 96% efficiency. Ductless heatpumps can't generate enough heat when it's -30, they're good to about -10c. Still wouldn't bother.

I've spent hours trying to resolve ductless problems when they arise, it's ended up being boards (there are multiple) or compressors. The electronic expansion valves have been reliable.

Thanks for the tips! Yeah, everyone mentions how quiet they are but honestly have you ever sat there and thought "Damn, my forced air system is loud?" yeah, me neither.

I wouldnt say I want a forced air system. I want a reliable, efficient, and effective system. What form that takes I'm totally open to. I've yet to be convinced that a ductless mini split can outperform a properly designed and installed forced air system. But again, i'm totally open to being convinced otherwise.

[vreihen16]

We live in a small 2BR house, that has an oil-fired Energy Star baseboard hot water heating system. Three years ago, we did a DIY install of an 18,000 BTU ducted "ductless" heat pump system, which uses the ductless compressor and stuff in a small air handler. Dropped our summer electric bills by over half compared to two window AC units, and trimmed 25% off of our heat costs in the winter.

The heat pump is rated for -4F at the low end, but in reality it starts struggling below 15F in our setup. We wind up running the oil system for 1-2 weeks every winter because we have it, to handle upstate NY's cold snaps. The heat pump and a few electric heaters would probably do us fine if we didn't have the oil system for heat (and use it for hot water as well).

With that said, the ducted "ductless" costs twice what a traditional ductless system does. We didn't have the wall space for a ductless air handler in any room. There are the usual wall-mounted air handlers, as well as floor-mounted ones, recessed ceiling units, and the ducted "ductless" that we used:



A ducted "ductless" system, concealed in ceiling headers:



The plans for our SC Garage Mahal call for using ductless and multiple compressors throughout for redundancy in case one fails. SC does not see the winter lows of NY, but does get a bit warmer in the summer. From experience with the current system, I'm going to upsize one level over the recommended size for each unit just to have the reserve capacity.....

[DETRoadster]

Originally Posted by vreihen16

We live in a small 2BR house, that has an oil-fired Energy Star baseboard hot water heating system. Three years ago, we did a DIY install of an 18,000 BTU ducted "ductless" heat pump system, which uses the ductless compressor and stuff in a small air handler. Dropped our summer electric bills by over half compared to two window AC units, and trimmed 25% off of our heat costs in the winter.

The heat pump is rated for -4F at the low end, but in reality it starts struggling below 15F in our setup. We wind up running the oil system for 1-2 weeks every winter because we have it, to handle upstate NY's cold snaps. The heat pump and a few electric heaters would probably do us fine if we didn't have the oil system for heat (and use it for hot water as well).

With that said, the ducted "ductless" costs twice what a traditional ductless system does. We didn't have the wall space for a ductless air handler in any room. There are the usual wall-mounted air handlers, as well as floor-mounted ones, recessed ceiling units, and the ducted "ductless" that we used:



A ducted "ductless" system, concealed in ceiling headers:



The plans for our SC Garage Mahal call for using ductless and multiple compressors throughout for redundancy in case one fails. SC does not see the winter lows of NY, but does get a bit warmer in the summer. From experience with the current system, I'm going to upsize one level over the recommended size for each unit just to have the reserve capacity.....

Thanks for the input! I had a really sweet oil fired boiler system with Euro style radiator panels in my house in NH. I recall electricity being really expensive out there. I'll need to crunch some numbers based on electricity and natural gas rates here in WA. My sense is there's not much of an advantage one way or the other but I could be wrong. Seattle's climate lends itself well to the mini split. If we get below 25 in the winter people begin to freak the F out. LOL.

So what's the benefit of the ducted ductless? Seems like you are locating all the guts outside the house at that point, so bonus points for easy maintenance I guess? You are investing in the duct system which seems to be the claim to fame that the ductless system avoids. So at that point, why not just run a conventional system?

[2000cs]

The most comfortable system in all the houses I’ve lived in was geothermal. This only makes sense when building because of the wells you have to drill, but it is quiet and comfortable heat-pump performance. No excessively dry air in winter, proper dehumidification in summer, broad ambient operating range. Central system with air ducts so typical at that end. Just no outside unit to decay and service. And very efficient.

[DETRoadster]

Originally Posted by 2000cs

The most comfortable system in all the houses I’ve lived in was geothermal. This only makes sense when building because of the wells you have to drill, but it is quiet and comfortable heat-pump performance. No excessively dry air in winter, proper dehumidification in summer, broad ambient operating range. Central system with air ducts so typical at that end. Just no outside unit to decay and service. And very efficient.

I'd love a geothermal system but that's not making the financial cut. I gotta draw the line somewhere!. I'm looking at $100k on driveway and utilities, $30k in tree removal, etc. A $25k HVAC system or $20k in solar panels just aint making the cut.

[Frostynorth]

Originally Posted by DETRoadster

Thanks for the tips! Yeah, everyone mentions how quiet they are but honestly have you ever sat there and thought "Damn, my forced air system is loud?" yeah, me neither.

I wouldnt say I want a forced air system. I want a reliable, efficient, and effective system. What form that takes I'm totally open to. I've yet to be convinced that a ductless mini split can outperform a properly designed and installed forced air system. But again, i'm totally open to being convinced otherwise.

Maybe not loud, but I certainly hear it turn on, and the air noise.


Because ductless systems are all variable speed, they're more efficient as they only use what's needed to achieve the desired temperature, where a traditional forced air system runs at maximum.

The hidden models are nice, but if not installed somewhere accessible on all sides, they are a giant pain to service. You could easily have a two or three head system and keep 2-3 areas of the house cool/warm as needed. I would say these are on par with the noise level of a regular forced air.

It would save money on electricity.

Originally Posted by DETRoadster

So what's the benefit of the ducted ductless? Seems like you are locating all the guts outside the house at that point, so bonus points for easy maintenance I guess? You are investing in the duct system which seems to be the claim to fame that the ductless system avoids. So at that point, why not just run a conventional system?

They are installed in a ceiling space 'hidden' away.

It's all efficiency, overnight your great room doesn't need to be kept the same temp as the bedrooms, the basement doesn't either. During the day the bedrooms can stay warmer.

[vreihen16]

Originally Posted by DETRoadster

So what's the benefit of the ducted ductless? Seems like you are locating all the guts outside the house at that point, so bonus points for easy maintenance I guess? You are investing in the duct system which seems to be the claim to fame that the ductless system avoids. So at that point, why not just run a conventional system?

I think that you're confusing a "package" system (air handler outside) with what we did.

Our house's small size means that the smallest conventional unit (2.0 tons) is overkill. At the time, we got 20 SEER (in a 1.5 ton system ducted "ductless") for less than a 14 SEER in a traditional 2.0 ton. The type of air handler that we used is on the right in the first picture above.

The previous owners sealed up all attic access in our single-story house, and I have no inclination to open it up and find out why to route stuff down through the ceiling. We also do not have free wall space for a traditional (cheap option) ductless air handler. Our only option was to come up through the floor from the basement, with ducts of some sort.

We hung the ducted air handler in the center of our basement (more like a crawl space, and ran sheet metal ducts to all four main rooms...poking up through the floor. I fabbed up a custom sheet metal return plenum to the basement through a kitchen cabinet, as well as a custom sheet metal distribution/splitter plenum for the outlet side of the air handler. All in, we did the whole duct install for ~$150 in materials at the big box store. Some surplus air handler insulation and scrap insulated flex duct showed up at our door from a friend, which we used to insulate the ducts and air handler.

The one pitfall of the ducted "ductless" system is that it was designed for use like in the second picture above with no restrictions and short duct runs. The fan can't build the full pressure of a traditional air handler, so everything had to be engineered with minimal duct bends and restrictions. Flex duct has more restrictions than sheet metal ducts, and believe it or not sheet metal is cheaper because HVAC contractors are apparently lazy and go for the flex duct. The sheet metal not only saved us money, but it also gave us the ability to have the ducts cleaned in the future without having the worries of tearing a flex duct liner out.

I had to learn duct sizing and engineering, the sheet metal trade, and even went to get the EPA certification so that I could legally handle the refrigerant. Considering that I had never even lived in a house with central AC or forced air heat before, this was a *huge* learning experience. My in-laws thought that I finally lost my marbles when I started this project, but now they come into our house for visits and comment how cool it is on the warmest summer days. (I jokingly said to my FIL when the AC was finished that my next DIY project was going to be 20 solar panels on our detached garage roof...which would be way easier than the heat pump project.)

For our SC barndominium project, using 2-3 single-zone mini split compressors is my first choice. Since we are going with an open concept (warehouse/industrial) house concept, I also have the option of using a traditional HVAC system with exposed ducts hanging from the ceiling. Of course, we would lose the failure redundancy with a traditional unit.....

[tdott]

I have a cool only one installed in my garage here in FL.

Paid $450 for it and installed it myself, 3yrs old and no issues
yet my central AC unit only 5 years old had it's cool replaced and always has drain line issues. I like the mini splits, units are much quieter inside and out. I would put one in my master bdrm and one in the living room if I could, would allow more fine control.

Now there are some expensive Mitsubishi or Panasonic ones that cost several thousand installed. The one I went with is cheap enough if anything happened I'd throw it away and install another.

I'd use them as a supplement to a central air system but probably not as a replacement, but that is in FL where we don't really need any heat.

[tgrundke]

We have a multi-zone'd minisplit in our ~1800 sq. ft. home that has a boiler for heat and no ducts. Dining room has a larger unit, then each bedroom upstairs (3), and it does a good job. The only time it struggles is when the temperatures get 85+ with high humidity.

We got a Daikan system and I'm impressed with the quietness and efficiency. Our bills in June+July went up about $30/mo. over usual. We can vary the system based on need in each room, so that helps the efficiency.

We also like that the compressor outside is virtually silent - even when it's running at full tilt. As compared to my neighbor's brand new Carrier unit, which we can hear run at all times.

The only downside, apart from the wall mounted unit "look" if it bothers you, is that Daikan does not have a good central/internet based management portal for the units - they all need to be controlled individually.

TL;DR: If you want to be able to control each room individually, I think mini-splits are the way to go. Otherwise, if you already have duct work for a furnace, it may just be simpler to go the route of a standard system.

[chassis]

I have experience with split systems in commercial office applications.

The benefits are efficiency and individual zone (room) control. What are the reasons your architect is selling you on them? Does he get a commission from the distributor? Ask him.

The architect can and likely has done the calculations to size the units to adequately cool the zones. If you doubt this then find another architect because this is an entry level calculation.

Tubes for refrigerant are insulated.

We prefer Mitsubishi, with Bosch a second choice.

Noice is different. I have been able to hear central forced air AC units in all houses I have lived in. Some quite loud in fact with booming duct sheet metal. Split systems will have a different sound as compared to a central force air system. Whether it is better or worse is your call. I don’t mind the sound of a split system.

[DETRoadster]

Originally Posted by vreihen16

I think that you're confusing a "package" system (air handler outside) with what we did.

Our house's small size means that the smallest conventional unit (2.0 tons) is overkill. At the time, we got 20 SEER (in a 1.5 ton system ducted "ductless") for less than a 14 SEER in a traditional 2.0 ton. The type of air handler that we used is on the right in the first picture above.

The previous owners sealed up all attic access in our single-story house, and I have no inclination to open it up and find out why to route stuff down through the ceiling. We also do not have free wall space for a traditional (cheap option) ductless air handler. Our only option was to come up through the floor from the basement, with ducts of some sort.

We hung the ducted air handler in the center of our basement (more like a crawl space, and ran sheet metal ducts to all four main rooms...poking up through the floor. I fabbed up a custom sheet metal return plenum to the basement through a kitchen cabinet, as well as a custom sheet metal distribution/splitter plenum for the outlet side of the air handler. All in, we did the whole duct install for ~$150 in materials at the big box store. Some surplus air handler insulation and scrap insulated flex duct showed up at our door from a friend, which we used to insulate the ducts and air handler.

The one pitfall of the ducted "ductless" system is that it was designed for use like in the second picture above with no restrictions and short duct runs. The fan can't build the full pressure of a traditional air handler, so everything had to be engineered with minimal duct bends and restrictions. Flex duct has more restrictions than sheet metal ducts, and believe it or not sheet metal is cheaper because HVAC contractors are apparently lazy and go for the flex duct. The sheet metal not only saved us money, but it also gave us the ability to have the ducts cleaned in the future without having the worries of tearing a flex duct liner out.

I had to learn duct sizing and engineering, the sheet metal trade, and even went to get the EPA certification so that I could legally handle the refrigerant. Considering that I had never even lived in a house with central AC or forced air heat before, this was a *huge* learning experience. My in-laws thought that I finally lost my marbles when I started this project, but now they come into our house for visits and comment how cool it is on the warmest summer days. (I jokingly said to my FIL when the AC was finished that my next DIY project was going to be 20 solar panels on our detached garage roof...which would be way easier than the heat pump project.)

For our SC barndominium project, using 2-3 single-zone mini split compressors is my first choice. Since we are going with an open concept (warehouse/industrial) house concept, I also have the option of using a traditional HVAC system with exposed ducts hanging from the ceiling. Of course, we would lose the failure redundancy with a traditional unit.....

Got it. So your install in an existing structure dictated some of your choices. if you were doing a "clean sheet", new build, like I am, would you do it all over the same again?

[DETRoadster]

Originally Posted by chassis

I have experience with split systems in commercial office applications.

The benefits are efficiency and individual zone (room) control. What are the reasons your architect is selling you on them? Does he get a commission from the distributor? Ask him.

The architect can and likely has done the calculations to size the units to adequately cool the zones. If you doubt this then find another architect because this is an entry level calculation.

Tubes for refrigerant are insulated.

We prefer Mitsubishi, with Bosch a second choice.

Noice is different. I have been able to hear central forced air AC units in all houses I have lived in. Some quite loud in fact with booming duct sheet metal. Split systems will have a different sound as compared to a central force air system. Whether it is better or worse is your call. I don’t mind the sound of a split system.

I'll ask him. He said they are using them a lot in their LEAD and "green" builds and getting away from natural gas in general He's also big on induction stoves over gas ranges (another point I'm not sold on).

He knows that ceiling height in the basement shop below is a big deal for me so the lack of duct work is a good thing. Also, he knows we are on a budget so I think in general the mini-split system ends up a little more cost effective than a furnace, an AC unit, and all the duct work.

[chassis]

Yes LEED likes efficient and the zone control and variable fan speed both contribute to efficiency. Induction heating is similar, more electrical energy goes into useful heat vs gas stove which heats the air as well as the cooking implement.

Look to Europe for residential energy efficiency. Induction cooking ranges are common there. Sounds like your architect is up on these things.

[overcoil]

Had Mitsubishi ductless in my last house. The house was a very open design and the cooling was excellent. Also the exterior unit was small and architecturally it was almost unnoticeable and didn't mar the minimalist exterior design. This was an earlier system and didn't have heat.

The one thing about the maintenance was, that I needed the HVAC people to come out yearly and disinfect the inside of the indoor unit. They sprayed a disinfectant over the coils and had a drip bag underneath, a very extensive cleaning regimen. If this cleaning wasn't done a fungus formed on the moving vanes etcetera and the unit would spew out water droplets.

[vreihen16]

Originally Posted by chassis

Noice is different. I have been able to hear central forced air AC units in all houses I have lived in. Some quite loud in fact with booming duct sheet metal. Split systems will have a different sound as compared to a central force air system. Whether it is better or worse is your call. I don’t mind the sound of a split system.

Our system is actually super-quiet, even with the fan running 24/7. I can hear our refrigerator and near-silent Bosch dishwasher over the air handler near the return plenum, and no noise whatsoever at the outlet vents. When I was visiting a friend's house a few years ago, I noticed that their traditional central AC unit was noticeable whenever the fan kicked on.

Originally Posted by DETRoadster

Got it. So your install in an existing structure dictated some of your choices. if you were doing a "clean sheet", new build, like I am, would you do it all over the same again?

As I wrote, my preference for our future "clean sheet" build is 2-3 single-zone split units for redundancy, and +1 oversizing each unit over what the recommended size is for each area being cooled.....

[vreihen16]

Back in the early 1990's, my employer had a high-pressure small-duct AC system installed in two office suites across the hall from my office at the time. It was supposedly the bleeding edge of AC technology at the time, using several ducts the size of vacuum cleaner hoses into each room. When it was new, the airflow was so strong that it used to blow papers off of people's desks!

Over time, the airflow dropped off noticeably. I was moved into one of those offices when the system was about 17 years old, and had to buy my own portable AC unit because the high pressure system couldn't even blow a draft in my new-to-me office any more. The HVAC repair guy (not trained on this system) said that the squirrel cage fan blades flattened themselves over time, which is why it could not move air. More likely, the ductboard and tape distribution plenum that the original installers fabricated blew apart over time from the high pressures, and was leaking in the ceiling.

Anyway, I'm mentioning this because these systems are still available from at least one manufacturer, and are being targeted as retrofits for historic/landmark buildings where the hoses can be routed inside existing interior walls. Definitely not something that I would use in a new construction, though.....

[DETRoadster]

Originally Posted by Caravaggio

The one thing about the maintenance was, that I needed the HVAC people to come out yearly and disinfect the inside of the indoor unit. They sprayed a disinfectant over the coils and had a drip bag underneath, a very extensive cleaning regimen. If this cleaning wasn't done a fungus formed on the moving vanes etcetera and the unit would spew out water droplets.

That sounds miserable!


Great feedback, everyone! We have a design review with the architect in a week. I'll dig into his recommendation for a mini-split further when we meet.

[TheWatchGuy]

Unless your house is small, mini-splits arent a great choice imo. They are great for cooling a room, but unless you only have a few rooms, or never go in some rooms, youre going to have some pretty big temp differences unless you install them in every room.

if i was going new build, forced air and ductwork would be my go to for anything with more than a few rooms. If i was retrofitting an existing house, minisplit would be the easiest and most cost effective way to do it. Or if i built a smaller house with only a couple bedrooms and an open space kitchen/dining/living room, might go for the minisplits. in my current house though with 3 floors (main, upstairs, basement), 3 "common areas" (Living room/kitchen, loft space, basement game room/bar room/tv area) and 6 bedrooms, putting in a bunch of minisplits wouldnt be a great choice over the traditional setup. We'd have 10+ units around the house.