Mini-Split or Conventional for HVAC?

[JFoy]

Thanks to everyone for the advice thus far.

One thought I've considered if I go with mini-splits is to buy two dual head systems. That way, if one compressor goes out, I would have some degree of redundancy.

The comments about oversizing a conventional system are true here as well - the contractors all want to do that. They say that with the variable speed fans, an oversized unit will be fine as the fans run at low RPMs. Plus, they say that if I want that extra umph of cold air during a hot summer, the unit can do it. I suppose there is an argument there.

Still, I can't help but think of all the ceiling penetrations for the supply ducts and resulting air leakage points. And I might be overthinking it too much given the building is sealed with the 1in spray foam.

Point for the conventional unit is freshening the air better. While some mini-splits do have a fresh air exchange, we'd have to use the ceiling fans all the time to stir the air whereas a conventional unit would do a better job by default. My wife and I smoke plus have two cats so I have to wonder if a mini-split can clean the air as well. I know some of the mini-splits can be equipped with HEPA filters.

The praises of the mini-split efficiency and low operating cost wins hands down. I have to wonder about servicing the units though - is it as easy to service a mini-split as a conventional unit.

 

[SirReal63]

Thanks to everyone for the advice thus far.

One thought I've considered if I go with mini-splits is to buy two dual head systems. That way, if one compressor goes out, I would have some degree of redundancy.

The comments about oversizing a conventional system are true here as well - the contractors all want to do that. They say that with the variable speed fans, an oversized unit will be fine as the fans run at low RPMs. Plus, they say that if I want that extra umph of cold air during a hot summer, the unit can do it. I suppose there is an argument there.

Still, I can't help but think of all the ceiling penetrations for the supply ducts and resulting air leakage points. And I might be overthinking it too much given the building is sealed with the 1in spray foam.

Point for the conventional unit is freshening the air better. While some mini-splits do have a fresh air exchange, we'd have to use the ceiling fans all the time to stir the air whereas a conventional unit would do a better job by default. My wife and I smoke plus have two cats so I have to wonder if a mini-split can clean the air as well. I know some of the mini-splits can be equipped with HEPA filters.

The praises of the mini-split efficiency and low operating cost wins hands down. I have to wonder about servicing the units though - is it as easy to service a mini-split as a conventional unit.

We have two three ton Mitsu's with 8 heads to cover 3500 square feet, it has worked beautifully. It is a little more tonnage than we need but with a mini split there is no penalty for oversizing.

As far as working on them, to me it seems easier, there are no pieces of equipment in closets, all of the mechanicals are out in the open. I grew up working with my Dad who was a HVAC Tech. We have had our installer out twice since we had them installed, once because a mis-manufactured fitting slowly leaked the Puron out, it took him maybe half an hour to replace the fitting, pull the vacuum and re-charge, most of his time was with the vacuum. The second time one of the condensate level switches failed and a slow draining condensate line backed up. It took another hour to replace, half of that was yakking with me. No charge for any of it. It took two days to install them, one day to run the line sets and one day to run the head units and charge them.

Our 8 units just quietly sit here keeping this house the temp we set the thermostats for. We do use ceiling fans, one upstairs and three downstairs, to keep the air moving, I am not sure if they are really needed but I like having them. If we ever build another house, it will have the mini splits in them.

 

[LouNY]

I have two 36,000 btu Mitsubishi splits systems in my house with seven heads, it does an excellent job of cooling and a good job of heating in the early part of the season. I am glad that I had this system install.
That said it cost all most twice what a conventional systems were quoted at, the conventionals would have been using flex duct in a hot attic as no one wanted to quote running ductwork in the basement and crawl space.
The mini- splits have been much more efficient to run compared to the window units previously in use.
In your case, new construction, a compact house with future plans to split the house into two uses and being smokers with cats;
I would lean toward two small conventional systems with VFD's on the blowers mainly to get some air changes in the house and filtration of the air, good well insulated ductwork will distribute the cooling and heating in a compact dwelling with several rooms much more evenly. One unit if you don't split it in the future with powered dampeners and a few thermostats to zone the home garage areas.

 

[jaxs]

Sound's like you understand pros and cons of both systems. Since you are concurned about penitrations and the flex duct monster, I'll give you something to ask contractor about. Put an up-flow furnace/air handler in alcove behind 1/2 bath basin. Fur down hall ceiling and cut vents for each room. All outlets should have adjustable dampers in covers. There should be a considerable cost savings compared to attic ducts. Effeciency is better since duct isn't exposed to attic air temperature.

 

[Rustyiron]

I'm in a similar building, a big shop with a small living space. (about 900s/f) We added a mini split last year (outside unit with 2 "heads") and it's been one of the most satisfying money spent in a long while! Right now it's only in the mid 70's but very sticky. The de-humidfy setting is just wonderful.
Up here in the frozen north we use it for the "shoulder seasons" that's spring & fall for heating after/before we've shut down/fired up the wood boiler that heats our radiant system in both the shop & house.

 

[ovrszd]

Mini splits have their place. My wife struggles with the visual....

 

[wagne223]

For me, the best feature on mini splits is the ease for self installation.

For the most part, AC installers and sales think they can do something no one else can and they overcharge for it.

I ordered an 18k pioneer heat pump online for $800 shipped. I did the install then called a local AC company to come out to do the purge, vacuum and verify the refrigerant. They charged me $250.

Had they supplied the unit and installed, price would have been $3k

I plan to install 2 more mini splits , one in the bedroom and one in the living room.
For 2 reasons. 1. Backup in case the main central unit goes out. 2. I can run the minis on a generator when a hurricane comes through.

 

[cqaigy2]

For me, the best feature on mini splits is the ease for self installation.

For the most part, AC installers and sales think they can do something no one else can and they overcharge for it.

I ordered an 18k pioneer heat pump online for $800 shipped. I did the install then called a local AC company to come out to do the purge, vacuum and verify the refrigerant. They charged me $250.

Had they supplied the unit and installed, price would have been $3k

I plan to install 2 more mini splits , one in the bedroom and one in the living room.
For 2 reasons. 1. Backup in case the main central unit goes out. 2. I can run the minis on a generator when a hurricane comes through.

I can see where having ac might be pretty nice when it gets hot and humid and you've lost power. :thumbsup:

 

[Sigarms]

I'm a proponent of mini splits.

From what the OP has described, I'd go mini split myself.

Two single zone systems, one in the living room facing towards the kitchen, one in the bedroom. Perhaps a air exchanger in the bathroom for more ventilation from the kitchen/living area, or if that isn't possible, a 2 zone mutli zone for living area and kitchen with a dedicated horizontal ducted unit for for the bathroom and a dedicated system for the bedroom.

That said, mini splits are not the greatest thing since sliced bread. Right now I'm replacing an outdoor that is only two years old because the manufacturer does not have the compressor in stock and they're waiting for it to come off a slow boat from overseas. There a MANY issues to compare between both systems.

What's the difference between a power control board and a power filter board? For service, mini splits do require some expertise as they are nothing like a conventional system what guys are used to working on.

As much as people may claim how great multi zone systems are here, I have numerous horror stories (just like a conventional split unitary system).

First mini split I sold was Sanyo back in or around 94, before they changed names LOL

 

[ultrarunner]

For me, the best feature on mini splits is the ease for self installation.

For the most part, AC installers and sales think they can do something no one else can and they overcharge for it.

I ordered an 18k pioneer heat pump online for $800 shipped. I did the install then called a local AC company to come out to do the purge, vacuum and verify the refrigerant. They charged me $250.

Had they supplied the unit and installed, price would have been $3k

I plan to install 2 more mini splits , one in the bedroom and one in the living room.
For 2 reasons. 1. Backup in case the main central unit goes out. 2. I can run the minis on a generator when a hurricane comes through.

I have found HVAC work very expensive and more so when demand is up...

Thankfully... the only thing I have ever needed was a purge, vacuum and verify... quite reasonable.

Mom had qot quotes for a new furnace... the old one had a cracked heat exchanger and dated from the 1950's

All parts for the new furnace, sheet metal, duct sealing, permits came to $1250...

The inspector commented on how it was one of the best installs he had seen... always makes you feel good unless they tell everyone that.

I also downsized the replacement and no issues...