1 vs 2 mini-splits

[Robert Hartmann]

Any thoughts on which is better given roughly the same cost of installing one 24,000 btu mini split vs two 12,000. We are replacing a PTAC unit (HVAC like in hotels) with a mini-split for our sunroom. I was planning to build a woodshop (2 or 3 car garage), but the cost is more than I want to pay right now. In the interim, I'm using part of our attached 4-car garage for woodworking. My plan is to put up a wall in the middle and use one side for my shop. I want to put a mini-split in so I can work there year-round. The "new" 2-car garage and sunroom are almost identical in size.

The only difference in installation is the single unit would require a longer run for the lines to the sunroom as opposed to placing a second unit in the optimal location. The distance is still well within limits.

My HVAC guy says it's a wash. He installed two in his house, but said it was really only for ease of installation. I'm thinking the same. If I install two, the second one would be in the best location and require the shortest run for the lines. I already have 220v in both locations. Ideally I would put the garage unit at that other end of the garage. Unfortunately I don't have a good (inexpensive) way to get 220v there.

[Jim Becker]

For heating/cooling, it "should" be a wash. For cost, I suspect two units will cost more than one dual zone unit. You will also have to provision two separate 240v circuits if you put in two units vs 1 for the dual zone. Both indoor units are powered from the condenser/compressor unit(s) outside so the only routing you need to deal with relative to that is for the lineset for each inside unit including the control/power cable that comes with the unit.

Personally, I think I'd opt for the dual zone for the situation you describe because I believe it will cost less than two single units and provide the same end results.

[Lisa Starr]

If you go with two units, will you be able to move the "garage" one to use in the shop?

[Bill Dufour]

Two units make more sense to me. I assume there will be times some one will be in one room and no one in the other. Why pay to heat and cool both if only one is occupied? I suppose this also depends ion your lifestyle now and in the future. Kids in the house or not etc.
We have a spare bedroom I almost never go into. I have the hvac shut down in that room. Waste of money to condition it very much unless occupied when I can open the vent.
Bill D

[Chris Parks]

Two units, if a single unit breaks down you have no heating and cooling at all but if one of two breaks down at least you have something still working.

[Lee Schierer]

They also make systems that will cool/heat two different spaces via two different thermostats using a smart manifold syslem mounted inside the house with only one outdoor unit.

[Bradley Gray]

My brother in law manages a fancy hotel that has multiple mini splits with more than I head. They have an issue in the "tweens" seasons where one room wants heat and another wants cooling. Apparently, the whole system has to heat or cool, not both.

[Jim Becker]

They also make systems that will cool/heat two different spaces via two different thermostats using a smart manifold syslem mounted inside the house with only one outdoor unit.
I believe that's one of the two choices he's looking at...dual zone vs dual systems.

[Jack Frederick]

Fujitsu, which I am most familiar with, Two 12’s will be substantially more efficient than the single 24. Check the specs on the units specified, though 12’s can run on 15 A circuits, the 24 a 20 or 30A. I think you will get more even air/temp distribution on the 12’s

[Robert Hartmann]

Thanks for the input. First of all, I have an open 30 amp circuit located where the garage unit would go and the sunroom already has a 20 amp for the existing PTAC unit, so power is not an issue. I'm looking at either two units or a dual zone unit as Jim mentioned.

A couple good points about usage/load needs. The sunroom will be heated/cooled year round. The garage unit will probably only be needed for extremes not to mention I have a wife, three kids and a job (for a couple more years), so woodworking time is sparse. Seems more logical to have two units. One would get a lot more use than the other so that might save wear and tear on one of them.

[Ronald Blue]

I put two 18,000 units in my shop. It wasn't only a little more expensive than one large unit. While my shop is very well insulated I wanted the better cooling that two separate units give. While a two head unit could have been done the installation would have been much more challenging. Home Depot had the best price last summer on Mr Cool.

[Jim Becker]

Home Depot had the best price last summer on Mr Cool.
Costco. :)

[Ronald Blue]

Costco. :)

The closest Costco is 2 hours from me. I have a Sam's membership but they were out of stock there.

[George Yetka]

Jim they are not always powered by the condenser. That is different amongst all the systems.

Lee they are called VRF or Variable refrigerant flow. And are a waste of money IMHO for residential use for a sunroom and a garage both are going to want heat or cooling at the same time. The VRF systems are beneficial in office settings where 1 room may be an IT room and the next an office. For the application Robert is talking about I would say 1 condenser and 2 heads without VRF.

Robert you may want to jump up the size of the garage unit to 18,000 btu. 12000 sounds like it sized for maintaining temperature. For me shop use is not an all day everyday event, I would want it to adjust temperature a little faster

[Jim Becker]

Jim they are not always powered by the condenser. That is different amongst all the systems.

Good to know but sounds strange to me. Both the Daiken and MrCool systems I've owned have been setup that way, but I suppose other brands could certainly provide power to the interior units separately. But you still need the control cables back to the outside unit so that would seem inefficient for separate power since the interior units use very little power compared to the outdoor unit.

[Jack Frederick]

The beauty of the vrf is that they are the units that offer the efficiency and comfort. Going single stage will not deliver the higher efficiencies and comfort. As you describe your use two units are definitely better for you. The suggestion to go with an 18 has some merit, but 12, 15 or 18 will all deliver the comfort. If you go on the low end and worry about the pick-up heat, most are wireless and you can control them on your phone so you can start them up, get ready and then go out to the shop and work in comfort.
The way these work is the 14-3, again on my Fujitsu units, runs from 1,2 & 3 on the condensing terminal block at 220v to the evaporator. 1 & 2 are power and 3 is a communication leg. That control circuit uses the 2 & 3 legs. All the controls are in the condensing unit. Compressor speed, condenser fan speed, and expansion valve position are all controlled by the condensing unit. The indoor evaporator is sensing room temp on the coil and the fan speed modulates based on the input from the condensing unit. Frequently on AC systems the refrigerant lines are called liquid and suction lines as the expansion device is in the evaporator. On mini-splits, the expansion valve being in the condensing unit the two refrigerant lines are both gas lines.

[Doug Colombo]

We installed a 18K single zone unit up north (Michigan) and have loved it. Two condos in our complex installed dual zone units and have had a few issues with them if settings were way different between the inside heads (one heat, one cool or large temp differences). My vote would also be for two units. I agree with both Bill and Lisa - why pay to run a larger unit when you may not need heat / cool in the garage at that time and also two units gives you the ability to move one unit to your shop if you want. Good luck and based on my experience with them (5 years), you will love it.