Ductless mini split HVAC vs NE Ohio climate

I'm drawing an addition out the side of the house for a bedroom, open area for both kids to have their stuff, a laundry room, and a basement below it.

my house is 1500 square feet right now with an oil furnace and 3 ton heat pump.  Less than 400 square feet is basement, the rest is dirt floor crawlspace.  The ductwork is pitifully designed and does a poor job of maintaining velocity and keeping the rooms are temps anywhere near remotely similar to each other.  I'm not sure a complete redesign of the duct system is the correct thing to do because of the age of the house and the fact that the crawlspace is gross and there is plenty of asbestos tape in the system that I don't want to disturb.  
 

which brings me to mini split systems.  I'm seeing more and more of them around here.  I'm 20 miles south of Cleveland so my normal heat pump works down to around 28 degrees without having to kick on the oil for backup.  Below that it produces heat but then runs the AC to defrost which negates the heat and it's an expensive cycle of nothingness.  The oil heats quickly but is expensive and less consistent.

the mini split is essentially a small heat pump.  Do they run into the same inefficiency issues at cold temps that large heat pumps do?  I like what I see from them, but if the addition will be basically unheated when it's colder than 28 out i can stop looking right now.

thanks

In my experience, when the outdoor temp gets down under (approximately) 20 degrees F., the system will bring in auxiliary heat.  Also, the cycle time will be long near the threshold where aux. heat comes in.

I see the sales literature touting "acceptable" performance at below 0 deg. F. temperatures, but I don't believe it.  Even in a climate as moderate as Richmond, VA, you will not see heat pumps installed without auxiliary heat. 

Edit:  How big is the addition?  Electric "strip" heat is the easy button (available in a mini-split?), but not cheap if it's on all the time.

They are an interesting concept, but not cheap. Mitsubishi and Trane are the same and offer "hyper heat" as an option. By the time you buy a system and install it, you could nearly buy a new gas furnace and new ducting for the whole house.

A small stand alone furnace may be the cheapest and simplest answer. Used stuff is out there on the cheap.

We had mini splits installed in our guest house, and liked them so much we put them in upstairs in our main house. We opted for the Mitsubishi system. The ones in the main house are the ceiling cassettes, so they're less visibly intrusive than the older, wall mounted ones. They were also slightly more expensive upfront.

Mitsubish literature touts 100 pct of heating capacity down to 0F. We don't get that cold here in rural Maryland, but we have seen temps into the teens and the units have kept our houses perfectly comfortable, even with no wall insulation and crappy insulation everywhere else.

For the 3 units in our main house, the system ran about 14k installed. Mitsubishi runs occasional Mr rebates, and we also got a energy credit rebate from our local utility.

We're such ballers that we put a Fujitsu mini-split in my wife's barn to heat/cool her tack room, and more importantly to keep the plumbing inside from freezing during Iowa winter conditions.  

It just went in this summer, so no extended assessment of how well it works at sub-zero temps, though it played fine through the first sub-zero spell we've had this year without the separate ceiling mounted re$i$tance heater kicking in. 

We did select a model from the catalog that was designated for operation at lower temperatures than the standard model.  If I recall correctly, the external portion of the unit also has metal fan and fan guard assembly that's supposed to be more robust with respect to ice.

So, anyway, take a look at the spec options when you're looking at one to install.

The most recent generation of minisplits is supposed to work at lower temperatures than they used to, I think some of them are good down to zero degrees F before the auxiliary electric heat strips kick in.

As far as traditional furnaces go, we don't have gas available on our street so that's a no-go.

Adding 600 square feet per outside dimensions.  I'm trying to weigh all options right now.  The heat pump was sized with adding on in mind.  In the end the correct thing may be to properly redesign the system from the plenum out.  I'm familiar with ductwork design enough that i can lay it all out and have done so before.

I have installed several of them and never had a problem with them not producing heat, even down into the teens temp wise. Granted I'm a lot farther south than you are and temps that low are not a frequent occurrence. My current heat pump gives up when temps get into the 20s.  

The brand I'm most familiar with is Klimaire. They advertise 100% heating capacity in temps down to 5 degrees F and reduced capacity down to -22.

It's not a major US brand and their pricing show it. The last unit I put in was a 18000 BTU, 21 seer for my father. It was just over $1000. Looks like they are in the $1200 range now. It takes 2-3 hours to install one. 

I just put an 18K BTU Mr. Cool DIY in my garage.  Hasn't been cold enough to test much below 30 degrees yet but it gets the garage up to temp pretty quickly.  When I was looking at them, it seemed most of the better units advertised full heat down to 5 degrees.

What about PTAC units (hotel style heat pump and A/C)?  Seems like there should be an ample supply of used units out there.  

Disadvantages versus a mini-split would certainly be the thru-wall mounting, but it has an advantage over a mini-split in that there is no refrigerant line plumbing required and no need to mount the condenser unit.  Another bonus would be no need to have a HVAC technician hired to charge the refrigerant.

In reply to engiekev :

PTACs can be noisy- the nice thing about the mini split we got is it's essentially silent.  For a garage or shop or something I'd consider it, or if $$$ is a factor, but otherwise, they kinda are a little bit terrible.  

Have a friend who is an hvac tech and his boss sells me only the quantity of refrigerant used at cost plus he takes his van home on weekends so that's easy.  With the heat pump i did the install except for the line set.  

In reply to Patrick :

The minisplits I have installed come pre-charged for 25' of line. All you have to do is hook up the lines, evacuate the lines and air handler and open the valve.  

Toyman01 said:

I have installed several of them and never had a problem with them not producing heat, even down into the teens temp wise. Granted I'm a lot farther south than you are and temps that low are not a frequent occurrence. My current heat pump gives up when temps get into the 20s.  

The brand I'm most familiar with is Klimaire. They advertise 100% heating capacity in temps down to 5 degrees F and reduced capacity down to -22.

It's not a major US brand and their pricing show it. The last unit I put in was a 18000 BTU, 21 seer for my father. It was just over $1000. Looks like they are in the $1200 range now. It takes 2-3 hours to install one. 

Dang that's a great tip! I might have to check them out for my garage...

In reply to Toyman01 :

Ah that is good to hear, I was perusing videos on installations and I was puzzled why you would have to charge the system at all. Kind of defeats the purpose of mini splits if you have to pay HVAC techs to get involved.

engiekev said:

In reply to Toyman01 :

Ah that is good to hear, I was perusing videos on installations and I was puzzled why you would have to charge the system at all. Kind of defeats the purpose of mini splits if you have to pay HVAC techs to get involved.

Klimaire's warranty states a HVAC tech should do the install. I haven't had an issue with installing them myself though. I had one in my previous house that lost a controller due to a lightning strike. They replaced the parts no charge, even though it was out of warranty.

My heat pump was charged for 25' but we needed 35' of line so it needed a little bit.

thanks for the tip toyman on the brand, their pricing isn't bad at all.  I'll likely look into one for the garage work area too