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setaG_lliB
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Air conditioning: Dual-zone mini split vs two portable units

Sun Jul 08, 2018 12:26 pm

I'd like to finally add air conditioning to my house. I'm interested in cooling only the main level (around 1200 sq ft), as the basement manages to stay fairly cool even on the warmest summer days. I've also been told that my ~45 year old furnace isn't ideal for air conditioning. For these reasons (plus overall cost), I've ruled out central AC.

So what I'm thinking/hoping will work is strategically placing two 14,000 BTU portable AC units, or installing a 30,000 BTU "dual-head" mini split, where one outdoor compressor feeds two indoor wall-mounted blowers.

Obviously, the portable units have two major advantages:
-Cost. The LG units I'm interested in are only $550 CAD each, and no professional installation is required.
-Ease of use: Each unit is powered by a standard 120v outlet. They can easily be moved around, if necessary.

The mini split, on the other hand, would set me back $3000+installation. Would this be money well spent? I could get a third portable and still be well under $3000. I realize that the mini split would be a hell of a lot quieter, but in terms of cooling efficiency, are they that much better?
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Sun Jul 08, 2018 12:54 pm

The mini split will be miles more efficient as the hot side and cold side don't have to share the same box. It's also much more aesthetically pleasing (14,000 BTU window units will likely need an exterior brace), quieter, and just might be helpful at sale time.

I've got a Mitsubishi dual-head unit and it saved my sanity through the recent heat wave.
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Re: Air conditioning: Dual-zone mini split vs two portable units

Sun Jul 08, 2018 12:56 pm

Portable units are less efficient, and also need their condensation to be drained. My friend had a portable unit because he couldn’t afford a ‘real’ one and he built a little sump pump to drain the water. Is something to worry about that a built-in unit would automatically take care of. The portable unit was also much louder, which was fine for a grad school bachelor pad, but not terribly pleasant overall.

My advice would be to determine how many days you’ll need the AC. If there’s only a week or so of hot weather as there is in some areas, you can get away with portable units, but if you’ll run it for a few months, a more substantial investment is more worth it.

Can you get a unit that does AC and heat so you can supplement your old furnace? That way you get the benefit of AC and get to use the imequipmebt year-round.
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Re: Air conditioning: Dual-zone mini split vs two portable units

Sun Jul 08, 2018 1:37 pm

In my experience, all portable units are terrible. An in window AC uses air from the outside to cool it's hot side while a portable unit doesn't have that luxury. Instead, it uses the air of the room to cool it and then throws it outside. This creates a vacuum which will suck the hot air though all the cracks in the house, heating up every other room. I've been looking at mini splits myself, but could never really get the time together to do such a project. If you do go mini split, know that they also have heat pumps which do both AC and heat; which I guess as you have a furnace won't really matter.
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Sun Jul 08, 2018 1:41 pm

FireGryphon wrote:
Can you get a unit that does AC and heat so you can supplement your old furnace? That way you get the benefit of AC and get to use the imequipmebt year-round.
Every mini-split unit I've looked at is a heat pump, so they can be used both for cooling in the summer and heating in the winter. Whether that makes sense depends on the price of electricity vs the fuel for your furnace, and how cold it gets (they get increasingly ineffective as the outdoor temp drops below freezing). When I do the reno on my condo I will be installing one as the climate here in Seattle is pretty ideal for their range of operation and I currently have electric heat so there are rebates available from my utility (since heat pumps are more efficient than electric heating).

That said, pure air conditioners will get colder than a heat pump will, especially when the outdoor temp is very hot. So you do get something for the noise and inconvenience. (There may be mini-splits that also or only do "true" A/C -- but I wouldn't have seen those around here as they're really not necessary in this climate)
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Sun Jul 08, 2018 2:55 pm

Thanks for all the info! I guess that settles it, a mini split is the way to go.

A few of the units I looked at were heat pumps, though that feature would be of limited use up here. Winters are long and like to dip below -35C.

Is there any particular brand I should be looking at? So far I've seen units from Carrier, LG, Mitsubishi and Trane.
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Sun Jul 08, 2018 3:17 pm

I've never heard of dual head systems before. I live in south Louisiana, where a/c is a way of life here. Our summers are about 8 months long, and even winters can be very warm. Those dual-head systems look perfect for cooler climates.

If the systems are ductless, then the cooling coils must be in the head units themselves. I wonder what they do about condensation drain, if the coils are in the heads.
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Re: Air conditioning: Dual-zone mini split vs two portable units

Sun Jul 08, 2018 3:20 pm

The Swamp wrote:
If the systems are ductless, then the cooling coils must be in the head units themselves. I wonder what they do about condensation drain, if the coils are in the heads.
There's a drain line alongside the coolant lines that snakes out to wherever the heat pump unit lives and it piddles out there.
UberGerbil wrote:
That said, pure air conditioners will get colder than a heat pump will, especially when the outdoor temp is very hot. So you do get something for the noise and inconvenience. (There may be mini-splits that also or only do "true" A/C -- but I wouldn't have seen those around here as they're really not necessary in this climate)
When we bought ours, units with a single inside unit were cool-only whereas dual-head units were two-way heat pumps. As for cooling capacity, my Mitsu had no issue maintaining 65-68F in the recent Northeast heat/humidity wave. It will be interesting, though, once the power bill rolls in.

As for the heating capacity, we use that in the fall/spring when it gets a bit cold for a day or three and we don't want to turn on the central heat (natural gas-fired baseboard hot water), so we just nudge the bedroom up a few degrees.
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Re: Air conditioning: Dual-zone mini split vs two portable units

Sun Jul 08, 2018 4:58 pm

FireGryphon wrote:
Portable units are less efficient, and also need their condensation to be drained.

I had one that used the heat of the condenser to evaporate the condensation and blow it out the exhaust duct.

Ari Atari wrote:
In my experience, all portable units are terrible. An in window AC uses air from the outside to cool it's hot side while a portable unit doesn't have that luxury. Instead, it uses the air of the room to cool it and then throws it outside. This creates a vacuum which will suck the hot air though all the cracks in the house, heating up every other room.

Some have two ducts, allowing outside air to be pulled in to cool the condenser.

However, even if you find one with the above two features, I still wouldn't recommend portable units. Mine never worked particularly well, and the condensate evaporation system was really problematic (not to mention loud). First the float switch that turns on the pump that sprays the condensate over the condenser failed, resulting in a mess when the condensate pan overflowed. I fixed that, but eventually the condensate pump itself failed, resulting in another mess. I used it with a drain hose for a while after that, but eventually the blower motor seized up, and which point I got rid of that POS.
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Re: Air conditioning: Dual-zone mini split vs two portable units

Sun Jul 08, 2018 5:05 pm

The models I saw were 22-SEER units, which is pretty efficient. By comparison, my central air a/c is a 13-SEER. So they should not be particularly expensive to operate.
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Re: Air conditioning: Dual-zone mini split vs two portable units

Sun Jul 08, 2018 6:25 pm

I recently installed a minisplit myself (for an upstairs room) and have an old inefficient "central" ac for the downstairs.

1. installation costs can be brutal as a total percentage on any installation for any minisplit, particularly if you are just installing a single small unit.

2. if you want your warranty, you'll need authorized pro installation for that reseller. I had an authorized pro do just the termination on the line-set and testing for $300 to get my warranty.

3. you will need to account for zones (rooms) and their interaction assuming doors to rooms aren't always closed with good seals.

4. oversize your btu for your installation relative to guidelines.

5. make sure the coolant line is not far from any inside unit and the outside unit. Though 50 feet is the recommended maximum, I'd suggest less than 40 feet. Make sure the line is reasonably straight (between the units) and very well insulated right up to and around the inside unit with *closed*-cell foam. Also, I strongly recommend doing the same for the line-set extension of the inside unit (which is usually pre-wrapped, but not well). IF you don't do this then you can have a LOT of condensation either pouring down into the inside unit (exceeding the drainage design for the unit), or dripping out somewhere along the line. It should also be very well insulated right up to the connection on the outside unit as well. I had several problems with this, so if you can learn from my mistakes - all-the-better. :wink:

6. IF you are getting a pro to do the install, try and negotiate a flat-rate rather than a per-unit install rate if you are going to use more than 1 unit.

7. Generally it's advantageous to use more than one unit. You decrease your total/complete failure rate, you generally get a higher SEER unit for the btu, and typically you can place the outside unit closer to its inside unit. IF you shop it well, sometimes you can get within 1/3rd price increase.

8. Note that as a "heat-pump" any heating that your unit will provide for you in the winter is subject to failure at freezing conditions (..in point of fact though, it's not much more efficient on the heat-side than any other source of heating - so consider safe spot-heating with reasonable efficiency ratings in addition to your mini-split if your winters get colder than about 30 degrees Fahrenheit).

9. Consider an efficient underground (buried 5 feet) air-pipe (cast iron and paint it with enamel to limit rusting) for the side of the outside unit to draw from. (..I *really* wish I'd done this, but unfortunately I didn't have access to sufficient ground where I could bury pipe where I had to place my outside unit.) This is for a cool-air draw (from being underground) across the radiator rather than the typical out-side air temperature. Doing this (well) should not only extend the life of the unit (because the pump and fan are working much less), but also dramatically lower costs. (..obviously you'll need an above-ground (above flood-line) covered (for rain) opening for out-side air to be drawn-in.)
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Sun Jul 08, 2018 9:31 pm

CScottG wrote:
4. oversize your btu for your installation relative to guidelines.


You should not oversize AC or Heat Pump systems. While Mini Splits are generally true variable speeds and allow you to get away with a lot more, a properly sized system will last longer, cost less to install, operate more efficiently, and provide better comfort. In addition, oversized systems can result in damage to the structure they are installed in due to inadequate humidity control.

5. make sure the coolant line is not far from any inside unit and the outside unit. Though 50 feet is the recommended maximum, I'd suggest less than 40 feet. Make sure the line is reasonably straight (between the units) and very well insulated right up to and around the inside unit with *closed*-cell foam. Also, I strongly recommend doing the same for the line-set extension of the inside unit (which is usually pre-wrapped, but not well). IF you don't do this then you can have a LOT of condensation either pouring down into the inside unit (exceeding the drainage design for the unit), or dripping out somewhere along the line. It should also be very well insulated right up to the connection on the outside unit as well. I had several problems with this, so if you can learn from my mistakes - all-the-better. :wink:


Maximum length for a dual zone mini split is typically 82 feet per evaporator. The insulation provided from the manufacturer is sufficient to prevent condensation issues assuming the installation was done properly. Those units remove several gallons per day per ton of refrigeration by means of the evaporator coil alone. After 18 years as a HVAC Tech and Educator I have never come upon an evaporator overflowing due to "exceeding drainage design" for any reason, much less a poorly insulated line set, so this would be a first for me.

6. IF you are getting a pro to do the install, try and negotiate a flat-rate rather than a per-unit install rate if you are going to use more than 1 unit.


Get multiple quotes and negotiate the lowest price.

8. Note that as a "heat-pump" any heating that your unit will provide for you in the winter is subject to failure at freezing conditions (..in point of fact though, it's not much more efficient on the heat-side than any other source of heating - so consider safe spot-heating with reasonable efficiency ratings in addition to your mini-split if your winters get colder than about 30 degrees Fahrenheit).


Mini Splits can provide adequate heat well below freezing temperatures at a cost lower than all other sources of heat. Modern conventional central air units are able to efficiently heat all the way down to outdoor temperatures around 20°F(YMMV as all houses are different). The discharge air temperature from the evaporator units will often feel cold as they are at a temperature below normal body temperature. This can decrease your comfort level during the winter, but that is a different conversation.

9. Consider an efficient underground (buried 5 feet) air-pipe (cast iron and paint it with enamel to limit rusting) for the side of the outside unit to draw from. (..I *really* wish I'd done this, but unfortunately I didn't have access to sufficient ground where I could bury pipe where I had to place my outside unit.) This is for a cool-air draw (from being underground) across the radiator rather than the typical out-side air temperature. Doing this (well) should not only extend the life of the unit (because the pump and fan are working much less), but also dramatically lower costs. (..obviously you'll need an above-ground (above flood-line) covered (for rain) opening for out-side air to be drawn-in.)


Condensing units are not designed to be ducted in any form as the fan motors/blades are intended for low static applications, so I am unsure as to what you are getting at here. As an educator and technician I am well aware that have not seen everything and if you know of an install or have more information regarding what you describe here I would love to be educated on it.
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Sun Jul 08, 2018 10:26 pm

setaG_lliB wrote:
I've also been told that my ~45 year old furnace isn't ideal for air conditioning. For these reasons (plus overall cost), I've ruled out central AC......The mini split, on the other hand, would set me back $3000+installation.

How certain are you that your 45yo furnace will hold out until you can afford to replace it, after recently spending $3k+ on the mini-split? Single-zone central air isn't as ideal on multi-level houses (ask me how I know), but if you install a high-efficiency furnace with central A/C or a heatpump, you may be elligible for some combination of tax rebates/credits and an incentive from your utility provider. The savings in fuel will pay for the rest in a few years.
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Re: Air conditioning: Dual-zone mini split vs two portable units

Sun Jul 08, 2018 10:55 pm

ShadyDog wrote:
CScottG wrote:
4. oversize your btu for your installation relative to guidelines.


You should not oversize AC or Heat Pump systems.



I should have qualified my suggestions, based on my experience - that's south (..still US) and very humid. And while I was intending that, I should have also mentioned that the "guidelines" statement was relative to the generic guideline for the particular unit, not industry standard guidelines for a specific site/condition. Nor was I intending to suggest something in total that was substantially larger, or has every room that's "over-sized". (..ex. where the largest room (or 2 largest) often open to others is sized one size larger than suggested, and most other rooms meet that generic guideline.)
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Mon Jul 09, 2018 9:43 am

ludi wrote:
How certain are you that your 45yo furnace will hold out until you can afford to replace it, after recently spending $3k+ on the mini-split?

I'm glad someone else got red-flagged by this.
setaG_lliB wrote:
Winters are long and like to dip below -35C

It would seem that you have more to gain from replacing your existing furnace with a modern high efficiency unit, especially for the winter heating bills. And at that point, you're already most of the way to the hardware/cost of a mini-split. Also, I use my basement as a "cold-bank" in the summer. Setting the thermostat to "circulate" sucks cold air from the basement and pumps it upstairs to cool the house without having to run the compressor nearly as often.
And yes, you'll get an Energy tax break for updating your furnace. I'm pretty sure that's nation-wide.
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Re: Air conditioning: Dual-zone mini split vs two portable units

Mon Jul 09, 2018 9:52 am

DPete27 wrote:
Also, I use my basement as a "cold-bank" in the summer. Setting the thermostat to "circulate" sucks cold air from the basement and pumps it upstairs to cool the house without having to run the compressor nearly as often.

That is a clever idea. Not applicable in Florida, but pretty clever.
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Mon Jul 09, 2018 2:02 pm

The problem is, not only is the single-speed motor in the furnace unsuitable for AC, but apparently the ductwork would have to be resized as well. All of this seems overkill for 1.5 - 2 months of hot weather. Natural gas is fairly cheap where I am, so I'm not too concerned about replacing it yet.

CScottG wrote:
a bunch of helpful tips

Whew! Thanks for all the info. I'll take a closer look at all of this. Hopefully these units don't have to be babied too much.

DPete27 wrote:
Also, I use my basement as a "cold-bank" in the summer. Setting the thermostat to "circulate" sucks cold air from the basement and pumps it upstairs to cool the house without having to run the compressor nearly as often.

Interesting. I will definitely try that.
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Mon Jul 09, 2018 2:24 pm

I should clarify that my [not special] thermostat has fan settings of:
Auto = Fan on when AC/heat is on
Circulate = Fan runs for...about 10 minutes on, 20 minutes off, etc etc (if I had to guess), even if the AC/heat isn't required. This is a helpful energy saver compared to having the furnace fan running 100% or nothing when the inside temp is pretty sable at/around your desired temp setting. Obviously if it's really hot and the AC is running a lot, then the circulate timer gets interrupted by the AC needs and it ends up acting like the "auto" setting.
On = Fan is on 100% of the time.
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Re: Air conditioning: Dual-zone mini split vs two portable units

Mon Jul 09, 2018 3:22 pm

EDIT: Wrong thread.
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Mon Jul 09, 2018 5:47 pm

Just got the weekly e-mail from the utility. If their numbers are right (and how would I disprove?), running both outlets of a 30K BTU Mitsu split for a week of 95F/70F temps (at 65F/68F thermostat settings) cost me all of an extra $13, and that's at $0.1484/kWh. I knew they were efficient, but dayum!!
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Re: Air conditioning: Dual-zone mini split vs two portable units

Mon Jul 09, 2018 6:51 pm

Captain Ned wrote:
.......cost me all of an extra $13, and that's at $0.1484/kWh. I knew they were efficient, but dayum!!

$13 can buy a few potatos and mini glow sticks. Well done sir.
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Tue Jul 10, 2018 6:43 am

Wow. Most impressive.
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Tue Jul 10, 2018 12:52 pm

Captain Ned wrote:
Just got the weekly e-mail from the utility. If their numbers are right (and how would I disprove?), running both outlets of a 30K BTU Mitsu split for a week of 95F/70F temps (at 65F/68F thermostat settings) cost me all of an extra $13, and that's at $0.1484/kWh. I knew they were efficient, but dayum!!

Jesus. I think I’m paying around $65 a month to run a 15 year old Carrier central AC. But it’s Canada, so I guess you could say I’m paying $65 a year for air conditioning. :P
Like a good neighbor jackbomb is there.
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Tue Jul 10, 2018 2:37 pm

jackbomb wrote:
Jesus. I think I’m paying around $65 a month to run a 15 year old Carrier central AC. But it’s Canada, so I guess you could say I’m paying $65 a year for air conditioning. :P

Well, that's just about what I'd pay for a month myself but, like you, I don't have to run it all that often. I was just surprised at how low the extra cost was given it ran 24/7 out of both outlets for a week in some Floridian heat/humidity.
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Re: Air conditioning: Dual-zone mini split vs two portable units

Wed Jul 11, 2018 6:52 am

Captain Ned wrote:
The mini split will be miles more efficient as the hot side and cold side don't have to share the same box. It's also much more aesthetically pleasing (14,000 BTU window units will likely need an exterior brace), quieter, and just might be helpful at sale time.

I've got a Mitsubishi dual-head unit and it saved my sanity through the recent heat wave.


This may also give you a chance to put the compressor on the north side of the building in the shade...

That may save you 10% on your electric bill...

If you are going to spend any money at all I'd put it into insulation, upgrading the furnace, sealing cracks and leaks, and saving up for a geothermal unit.
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Re: Air conditioning: Dual-zone mini split vs two portable units

Wed Jul 11, 2018 9:40 pm

Captain Ned wrote:
jackbomb wrote:
Jesus. I think I’m paying around $65 a month to run a 15 year old Carrier central AC. But it’s Canada, so I guess you could say I’m paying $65 a year for air conditioning. :P

Well, that's just about what I'd pay for a month myself but, like you, I don't have to run it all that often. I was just surprised at how low the extra cost was given it ran 24/7 out of both outlets for a week in some Floridian heat/humidity.

For some reason I read that as $13/month. Guess I had a few too many beers. :lol:
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Re: Air conditioning: Dual-zone mini split vs two portable units

Thu Jul 12, 2018 6:05 am

DPete27 wrote:
I should clarify that my [not special] thermostat has fan settings of:
Auto = Fan on when AC/heat is on
Circulate = Fan runs for...about 10 minutes on, 20 minutes off, etc etc (if I had to guess), even if the AC/heat isn't required. This is a helpful energy saver compared to having the furnace fan running 100% or nothing when the inside temp is pretty sable at/around your desired temp setting. Obviously if it's really hot and the AC is running a lot, then the circulate timer gets interrupted by the AC needs and it ends up acting like the "auto" setting.
On = Fan is on 100% of the time.

Definitely saves energy, but my installer told me that circulate can have a negative effect on the life of the fan motor due to the frequent stopping and starting. I just keep mine on "On" all year round. More comfortable for me, and it doesn't cost us much more in energy with the high efficiency DC fan motor we have. And also my thermostat doesn't even have a "Circulate" function. :lol:
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Thu Jul 12, 2018 7:58 pm

Captain Ned wrote:
Just got the weekly e-mail from the utility. If their numbers are right (and how would I disprove?), running both outlets of a 30K BTU Mitsu split for a week of 95F/70F temps (at 65F/68F thermostat settings) cost me all of an extra $13, and that's at $0.1484/kWh. I knew they were efficient, but dayum!!

Sold! Which Mitsubishi unit are you using?
 
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Re: Air conditioning: Dual-zone mini split vs two portable units

Thu Jul 12, 2018 8:12 pm

setaG_lliB wrote:
Captain Ned wrote:
Just got the weekly e-mail from the utility. If their numbers are right (and how would I disprove?), running both outlets of a 30K BTU Mitsu split for a week of 95F/70F temps (at 65F/68F thermostat settings) cost me all of an extra $13, and that's at $0.1484/kWh. I knew they were efficient, but dayum!!
Sold! Which Mitsubishi unit are you using?

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Re: Air conditioning: Dual-zone mini split vs two portable units

Mon Jul 16, 2018 2:22 pm

jackbomb wrote:
Captain Ned wrote:
Just got the weekly e-mail from the utility. If their numbers are right (and how would I disprove?), running both outlets of a 30K BTU Mitsu split for a week of 95F/70F temps (at 65F/68F thermostat settings) cost me all of an extra $13, and that's at $0.1484/kWh. I knew they were efficient, but dayum!!

Jesus. I think I’m paying around $65 a month to run a 15 year old Carrier central AC. But it’s Canada, so I guess you could say I’m paying $65 a year for air conditioning. :P



Oof, most of the energy star stuff, even when not run in super-efficient mode will run you well under $200 a year to operate, and considering I'm only running mine 3-4 months a year in summer time, far less. I moved recently and have to buy a window unit for my home I rent. I'm sour about it because my less than 3 year old Mazda's AC just blows hot air now for reason unknown. I have to imagine a leak, or maybe worse that the evaporative condenser has **** the bed. :evil: So I'll be buying 2 AC's this week...
Corsair 600T | ASUS P8P67 PRO | Intel 2500k @ 4.4Ghz | Asus 1080GTX | G.SKILL Ripjaws Series 8GB | Corsair HX650 650W | Asus ROG Swift Gsync 27"

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