2 feet above grade and 6 feet below grade, with 2" rigid foam R5 which makes it R10, in NJ.

The right way to calculate this is with a load calculation. But I would think you would need less than 10,000 BTUs. A one ton mini split should be more than adequate.

From what you describe I would not expect your basement to be in the mid 50s in the winter. Is the basement ceiling insulated? What temperature do you maintain the first floor. Are there windows and are they double paned and tight?

Hi Mike,
Ceiling and walls to be put in and insulated so it should hold high 50's, low 60's thereafter I'm hoping. Decent windows cause home is 2 years old.

That's part of my decision 9K 3/4 ton or 12K/1 ton. 10K is in between

You don't have to insulate the basement ceiling if the floor up above is going to be heated. If the temperature on both sides of the ceiling is about the same then there is no heat loss. The only reason you might want to insulate the ceiling is for noise.

I am also in NJ and I finished about 550 sq. feet of my basement many years ago. Two walls are exterior facing, one is interior to the unfinished part, the other is exterior but all underground. The exterior walls are built with 2x4 with 3.5 inch batt insulation. That makes the insulation R-13. There is also an air gap between the insulation and the exterior wall.

On a very cold day the basement might be 64 degrees. I have eight 90W halogen lights in the ceiling (720W) which converts to about 2500BTU. If I turn all the lights on at full brightness I can raise the temperature to 66 degrees in about a half hour. If I turn on the 50 inch plasma TV the temperature rises faster. The point is it doesn't take much heat to warm up the basement.

That's a big price difference between 0.75 and 1 ton. I was taking an educated guess. The 0.75 ton should be fine. You will never use the mini split in the summer for cooling unless you have a lot of computer equipment giving off heat.

Mike -
Your comments are precisely what I was after and jives with my thinking. Thus recommendations of 18K I'm going to discredit. I may go 12K, just because it seems there's not significant oversizing as inverters seemingly regulate themselves.
Ceiling already has fiberglass batt and I am using rigid foam throughout, 2" for walls and 1" for ceilings. I plan to insulate the rim joists as well, and there are three 18" windows. But like you, I'm hoping that eliminates some heat loss and thus raises the average temp in basement.

Only one 70" LCD I'd imagine, and a refrigerator, so no real heat, I think, but certainly some, from those appliances. Agreed I probably don't need it for AC, mostly want to heat it up in winter and dehumidify in summer, which a lot of these units have the dry mode.

I'm looking at the 12K LG Art Cool Gallery with picture frame option

Sounds like a good plan. I would be interested in hearing how this turns out. Please keep us posted.

A little oversize is not bad. In fact, the variable-speed equipment operates more efficiently at partial load that flat-out. I would not go way over or it will start to short cycle too much. The floor is insulated? if you are going for using this mostly for heat, you might want to consider a floor unit rather than high ceiling mount. My experience is that the standard high wall equipment make good ceiling heaters when they throttle back and slow the blower down. Ceiling fans help a lot. My house, however, has very cold floors so the problem might be magnified.

If ceiling fans are not possible due to low overhead space, one of those quiet hassock fans placed near the standard high wall unit might do a lot of good.

Ionized,

this is basement so ceiling fans not feasible in my space. Basement floor will just be laminate on top of concrete slab.

By floor unit you mean radiant?

Yes mostly heat, but some AC and definitely some dry mode to reduce summer humidity.

In damp basements, dehumidifiers will be needed. Don't believe anyone that tells you that mini splits are dehumidifiers. They can be put into a mode that biases the operation to cooling or to dehumidification, but in the latter mode, cool will still be produced. That often means that you need to run a dehumidifier and AC (mini split) concurrently.

There are mini split indoor units that sit on the floor, the most common are the high mount wall models, and there are ceiling cassettes. For heating, the floor model will work better inherently. With the high wall models, some sort of additional circulation can benefit the heating mode in my experience. It should also boost the dehumidifying efficiency.

Ionized, never seen a floor model. Will look. Unless you have a recommendation of brand or model

So one contractor is stating that a higher btu unit will have a heat pump that operates in lower outdoor temperatures, and below a certain outdoor temperature a smaller unit will produce less heat?

"The output mostly depends on the outdoor temperature, but as you can see it does differ with indoor temperatures as well but very minimal.

It isn't a calculation of how much load is needed like it would be in manual J.

For instance if you take a look at the chart in the red box. It shows you the output for the 24 degrees farenheit outdoor temperature with indoor temperature of 64 degrees will only give you 9.51K BTU on the Art Cool Gallery unit. Which is not enough for your need of 12K you mentioned when the temperature goes that low."

In damp basements, dehumidifiers will be needed. Don't believe anyone that tells you that mini splits are dehumidifiers.

Ok everyone who challenged me should dog pile on the new rabbit.

https://www.youtube.com/watch?v=2cn-LWSmVjY

Newer designs allow heat pumps to operate relatively efficiently in colder temperatures. The Flash technology from Mitsubishi is remarkable. I really don't understand your post at all. Yes, at low temps the heat pump makes less heat and makes heat less efficiently. The size will still be determined by calculation. Fortunately, the heat loss in the basement will not vary with outdoor temperature very much, but heat production will suffer.

Sizing to heat may put you in oversize situation for cooling which is not ideal. You might want to size smaller and assume that on a few of the coldest days you will stay upstairs or put on two sweaters.

Ionized it's a guest room. 12K for sufficient heat, vs undersizing and struggling to heat. The compromise may be oversizing for AC as you mention. 3K difference should be too big a deal?

I wouldn't think a inverter mini split would matter much on sizing, because the unit is always going to be ramping up or down based on load of the structure (these are full variable speed systems in which the compressor ramps up or down based on load). With probably a 1000 different ways to go with in the mini split spectrum that is the harder choice to make IMHO. [This doesn't mean it will dehumidify a basement properly.]

I really suspect inverter technology will change a lot of things in this business over the next decade. The problem with over sizing is when you have a over sized single speed AC and low loads. The system short cycles and due to this creates an over supply of humidity.

Mini split technology on it's own changes so fast that these units have become what is known as disposable AC. They really aren't built or made for long term. Best case scenario that you could hope for is probably about 10 years. Then you go out and buy a new one.

Austin, thus is the reason I'm leaning toward 12k instead of 9K to ensure I get proper heating, which may oversize AC but hopefully inverter modulates that.

If your basement is like mine then the temperature will rarely go above 72 degrees during the summer. Don't expect to run the AC except in cases when you have several people and equipment generating heat.

I agree Mike. So only for like a summer party. So sizing for heat which may oversize for AC is what I'm leaning towards.

Be careful. Not all mini splits that I've see advertised have variable-speed compressors. Less expensive models are sold that are single-speed. As a point of interest, relatively recently, and maybe still there were DC-driven compressors as well. (They are reluctance motors rather than the more usual induction motors.)

There are a lot of subtleties involved in choosing the best mini split system within a brand and what brand to choose. As already mentioned, some work much better in low temperatures for heating. If it is very cold in your area, it will be worth the extra coin to buy one of these. Another factor is the ability to modulate output. Some modulate lower than others.

As an example of the subtle choices, say that you want to install 5 mini splits in your home. The largest residential compressor unit may support 4 indoor units so you may install one that runs 4 and one that runs 1 (or 3+2). Does it matter where you install the smaller compressor? Yes, the smaller ones are better installed to run a room or two that are most likely to be running by themselves with the larger system off. That would most likely be a bedroom or two and at night the system would have longer run times without shutting off compared to being hooked to a larger compressor that can't modulate to the same low minimum. Leave the larger compressor unit to run the units that condition the main parts of the house that is on when it is hot and everyone is active and moving around. Here is a pretty good article that discusses how to make some of these choices although I think that the setback advice is oversimplified:

http://www.greenbuildingadvisor.com/articles/dept/musings/how-buy-ductless-minisplit

Ionized, read the whole article. Good one. Thanks.

I'm specifically looking and deciding on these two LG Art Cool Gallery

LA090HVP AND LA120HVP

http://www.lg-dfs.com/art-cool-gallery.aspx/LA090HVP

http://www.lg-dfs.com/art-cool-gallery.aspx/LA120HVP

mini split has the market of confusion stitched up, because there are so many different ways. That being said I don't think I would ever come to a point in which I were to have a multi headed beast at my home. (multi zone with multiple heads or air handlers if you will).

Reason being this technology changes so fast and after a decade you're more likely to have to rip all of it out and start over. I view these things as maybe a secondary or special need type appliance.

The other thing about inverter type mini splits is the power source needs to be really good. If you have a lot of brown outs and power surges where you live it's in your best interest to fix those problems with a high quality surge protector. Those electronics are costly and typically only warrantied for maybe a year thru some manufacturer's.

I found this:

"Ueno and Loomis wrote, “One homeowner complained of temperature unevenness; when the data were examined, it was clear that they operated their MSHP [minisplit heat pump] in an ‘on-off’ manner, rather than using a fixed setpoint. This resulted in wide swings in interior temperature (between 60°F and 70°F+). The electricity use showed many hours with the MSHP running at maximum capacity, followed by periods with the unit shut off. When operated in this manner, the MSHP is heating at its least efficient (maximum output) state. Electricity consumption was a high consumption outlier; when compared with simulations, it was the worst-performing house (heating [energy] use 57% higher than simulation).”"

And another commented:
OK. LEt's say the ground freezes down to 2' so thats 4' at about 20°F, and a perimeter of 200' is 800 sqft at R-10. That is 800*50/10 = 4000 BTU/h

Let's say the bottom two ft of the wall are at 50°F, 400*20/10 = 800 BTU/h

Let's say the slab edge loss is a 2' wide strip 200' long and R-3 to 50°F it would be 400*20/3 = 2666.

If you add it up, you get 7500 BTU/h conduction at 20°F outside. This load would be well buffered by the underground thermal mass. If the temp fell for one day to 0°F, it would NOT increase proportionally (to (70/50)*7500 = 10,500). It would take days at that temp for the load to creep up, but the mini output would fall during weather that cold.

If the 9K put out 9K at 20°F, you'd be fine with a little margin, and it would throttle down as needed and not cycle too much.

If it would bug you if the basement got a little chilly during a cold snap (like 3 days in single digits) every few years, then go up one size. It will prob be slightly more efficient running at lower throttle.

Austin Air Companie, any evidence for this?

"The other thing about inverter type mini splits is the power source needs to be really good. "

airahcaz

I am operating on memory. I read the Uneno and Loomis case study considerable time ago. I think that those monitored homes were experiments in energy efficiency. They were built to be super efficient and have way above code insulation. They were small and may have all been two-story and at least some of them were. In order to keep equipment costs low, and get correct sizing, they decided to try to condition the homes with single mini split heat pumps. In the two-story homes, these were located at the top of the stairs. There were lots of (predictable) problems.

Downstairs is difficult to heat from upstairs. Upstairs is difficult to cool from downstairs. Doors need to be kept open for the most even temperature. (They monitored door open/closed state.) After failure, they added second units to some of the homes so they could heat from downstairs and cool from upstairs and continued monitoring.

Set-back advice from that study applies most to very-well insulated and air sealed homes. The heat transfer between rooms is very fast compared to through exterior walls so zoning and set-backs are not very useful. In an old, poorly-insulated, leaky structure, the calculations are different. How different depends on leak and other heat transfer rates.

How closely do the conditions of that study apply to your basement? In some aspects, pretty well. In others, maybe not so well. Set-back utility depends on heat loss rates and how long and deep the set backs are. (If you are out of the house for a month, a set-back is a no brainer.)

It bugs me that the manufacturers have not yet programmed a "set-back" recovery mode for their variable speed heat pumps where they'd operate closer to an efficiency sweet spot to bring the temp back up, albeit, more slowly. Residential boiler manufacturers have done it. You can do it manually by raising the temperature setting gradually, but who wants to do that?

Most recent HVAC installer is suggesting a 3-4 zone unit, vs. single zone, as if we need to heat bedroom (bathroom, future office, etc.) later, we'd have to replace the outside unit? This will double initial costs, materials and labor, but worth considering?

If I understand this correctly, run run, run, run away from this installer. They suggested that you install an outdoor unit with many unused taps so you can install more indoor units "someday"?

You should not install excess compressor capacity unless installation of more indoor units is on this side of the horizon. We've gone over enough excess capacity talk to rule that kind of action completely out. (Don't forget that you will have a lot of extra wear and tear on the compressor with frequent starts as well. I don't think that we have hit on that aspect yet.)

What kind of heating and cooling do you have in the rest of the house right now? Right now, heat pumps are not thought of as a good way to heat if natural gas is available. At a time, they were, but gas prices have gone way low. If you add the disadvantaged fuel cost and the equipment cost, you are really going in the wrong direction if you can heat with nat gas.

We have NatGas: a 2.5 ton for main floor (unit in basement) and a 1.5 ton for 2nd floor (unit is in attic). We don't want to "tap into" these, thus the ductless route.

As for multi-zone, it full well meant to provide for a bedroom and an office, both will be built as part of finishing basement, so a three-zone unit was part of the discussions, but we were going to forgo any heating needs assuming basement will be fine overall with a single 12K unit, supplemented with a space heater in basement if really necessary

Have done some research today and emailed and chatted with an on-wall heater manufacturer: Cadet. This is their newest model
http://thd.co/1MVRLk4 and has a digital thermostat that regulates output.

So perhaps Single zone in main living space and an in-wall heater (or even electric fireplace) for the bedroom and office which will have infrequent use when there's a need for additional heating in those winter months that guests indeed sleep over.

Power source needs to be really good.

Appliances --- any that you attach to a power source is rated for a certain voltage with 'some' tolerances. Usually 10% up or down of a rated voltage of the appliance. You go out side that envelope for any length of time or repeatedly for that matter and problems will develop.

I am not sure what kind of 'evidence' you are looking for... ride along with me isn't possible due to commercial insurance reasons.

So I leave you with this.... Mini split power surge among other problems

I have a manual that allows me to read LED codes on my units if I ever need to. It is way cool that it is so easy to diagnose these and then get the replacement parts directly from distributors. In addition to that, I have parts of my "system" still working just like the guy in the vid if one compressor or indoor unit goes down. In his case, three of four were keeping him reasonably comfortable.

Electronic components are certainly susceptible to power surges. It is an urban legend, however, that they are very sensitive to voltage fluctuations. The power supplies regulate the voltage to nominal at the points where it counts over a wide range of input. That probably extends to the motors in inverter-driven compressor systems.

P.S. I just watched another Youtube vid connected to the one posted. Mitsubishi has the troubleshooting info on their web site:

http://mylinkdrive.com

The problem with using a multi head unit is that the capability to ramp down to a lower speed (where maximal efficiency is) is much less if you have a larger compressor feeding 3-4 units.

I would put in a single 12000BTU in the main area and keep the doors open as much as possible. I would use a oil filled radiant heater in the bedroom as needed when someone is sleeping in there. Remember not to turn the thermostat down in the basement when not using the area as the mini splits use less energy operating at their lowest speeds; you will actually end up using more energy if you try to turn the thermostats up and down depending on usage.

" Remember not to turn the thermostat down in the basement when not using the area ....you will actually end up using more energy if you try to turn the thermostats up and down depending on usage."

That is way oversimplified. The energy effectiveness of set backs is dependent on several things, including the relative effectiveness of the equipment, heat transfer rates from the structure to outdoors, and the length of the setback period. For example, if the set-back period is a year, it will certainly save energy with variable speed compressors. I am relatively sure that a one month set-back would save money. How about a week, or a day? Most people go several hours.