I'm so confused over Mini-Splits, Central A/C and Heat Pumps

15 years ago

Can someone explain the difference between a heat pump, central air and heat and a mini split as far as cost of operation?

WeÂve been told by 2 companies that a mini split wonÂt work in our house but 2 other companies said it will. There would be 6 zones with the mini split in 1800 square feet.

WeÂve been told there is no benefit, cost wise, to having a mini split versus a central unit with 2 stage. We have 2 estimates so far and the mini split is less than $500 more than a central air and heat 2 stage unit.

We live in southern Louisiana. The house will have spray foam insulation in the roof, outer walls and under the floor, low E windows and doors, metal roof. No trees are close enough to shade the roof.

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Comments (5)

energy_rater_la
15 years ago
heat pump, central air and heat and a mini split as far as cost of operation?

heat pump same as central air and heat except that the heat pump provides the bulk of the heat.
this is what I recomend to my clients based on savings
compared to electric strip heat.
with heat pumps the electric strip is emergency heat and for when temps are 30 degrees..which is not that often for us.

central air is electric strip heating only. the most expensive way to heat your home. (espically if you have
entergy for your utility provider)

mini splits are pretty cool. expensive but fit a lot of needs and great for tight retrofit spots.
the condensing unit goes outside like with any set up,
but this is where it changes. in each room the air is provided by a wall mounted air handler unit. the condensing units are up to 3 tons. each room would have the
ahu..this is what they are calling zones.
cost is higher, but you don't have ductwork, so it evens out a little better.

with the foam insulation & low e windows your tonnage of ac required will be less. although I don't recomend 'rule of thumb' sizing
instead of the ususal 400 to 500 sq ft per ton, your
house will be more in the range of 600 to 700 sq ft per ton. oversizing will cost more to operate, wear the equipment out sooner, and will NOT dehumidify.
be diligent in finding out what is being spec'd for your home and what options are available for you.
some systems will qualify for tax credit, and it is always
a good idea to do better than the legal minimum allowed by law (code).
in what part of La. are you building?
best of luck.
kntryhuman
Original Author
15 years ago
Thanks for the explanation. We moved a 1300 sq ft 106+ year old house to Folsom and added another 575 sq ft. The addition is 10' ceilings, master bedroom, bath and laundry. The rest of the house is 8' ceilings, 2 small bdrms., 1 bath, dining, kitchen and den all open.

We are trying to do everything to get the lowest possible electric bills. We have Washington-St Tammany Electric.

We're seriously considering solar hot water and possibly electric. We will have a tankless water heater to start and use it as a back up.

The thing that's really confusing me is different companies saying they can't put mini splits because we would need 6. Then the other companies saying it's not a problem.

So if I understand correctly, the heat pump would be a better option.

What part of Louisiana are you in?

Thanks again.
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First off, 4 stories sounds like a big vertical head for residential mini-split equipment just from my casual notice of those requirements. I would check that out first. I am testing a whole-house mini-split installation right now (Mitsubishi, 7 in, 3 out). I will let you know in a year or so if I like it ;-) On paper they are more efficient due to inherent efficiency and the inherent zoned nature. We have been having pretty hot weather and with my wife out of town this week, I have been pretty much been cooling the bedroom and the kitchen with some intermittent cooling in the utility room where the exercise machine lives. Note that I am not much of a sit and watch TV type. You are really a leg-up over lots of others on this decision as you have experienced mini-splits. One thing to think about is that, IIRC, most of them don't have back-up heat so you will not have any heat while they are defrosting. (Maybe none of them have electric resistance back-up, but I think I ran across at least one brand that does.) You also have to pay close attention to cold weather performance for the mid-Atlantic region. I know that with Mitsubishi's current residential equipment, the 1:1 systems have better low temp performance than the multi-splits. They are more efficient too. Even if they do have back-up heat, you can kill the efficiency pretty fast if you need back-up very often. Keep in mind that there are lots of options to the wall-hung indoor units. They cost more, but there are units that can be dropped into ceilings and others that sit on the floor. There are also short, ducted units that would solve that big room problem by splitting the supply and return. (You could also install more than one indoor unit/room.) Condensate needs to be dealt with using pumps. I am not an HVAC or building pro, so take my observations with a grain of salt. After replacing a ducted system with mini-splits, and talking to my install guys a lot, here are some observations and conclusions. Installing a mini-split through outside walls, as is it usually promoted, is pretty quick and straightforward (read fast and cheap) compared to installing a new duct system in an existing house with no central AC. My install was done through interior walls running the lines/cables under the raised house and out to the side which was much more complicated. If I were doing this over and I had a good duct system within a house envelope, I would stick with it. The trouble is, what is a good duct system? More often than not, they are outside of the living space. In addition, they are considered good when they leak 5% of the air and they only get worse as they age. My system was in the attic with parts of the duct system in the attic and partly in a furred-down space over the hallway. The worst part was one duct that started at the AH in the attic, dropped down under the house in a chase and ran for about 30 feet before it reached the first floor register in an addition with a flat roof (thus no attic). It then reduced in size and ran another 25 feet under the house. That part might have been mini-splitted even if the rest of the house retained a ducted system. By your description, your duct system was not installed very well, but if the design is sound, it could be revamped less expensively than installing minis. In general, I think that ducted systems are trickier to design and install than mini-splits so there is more tolerance for less than careful and knowledgeable installers with mini-splits. Due to their ability to handle variable loads, choosing the right size is not as critical either. (I had 4 tons cooling plus a gas furnace before, now I have about 106% of the cooling and 60% of the heating. The heating was way oversized.) My system will handle cooling fine with the house the way it is, but I should not have trouble after I make improvements to limit infiltration and add insulation. My installer is knowledgeable, smart, very workmanlike, and experienced (he has taught the trade for 30 years). He would have installed new ducts and a two-speed system for a slightly lower price than the chosen mini-split equipment. I doubt that he would do it for the same price if doing it on a similar home going through interior walls. He did not have much mini-split experience and brought in a collaborator that does, on this project because he was looking forward to a learning experience. I don't think that he lost his shirt, but I don't think he made as much as he usually does.
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energy_rater_la
15 years ago
Near Lafayette. Born in st tammany parish hospital.
We moved a lot..Mississippi, then bogalusa.
then turned 'of age' and got the heck out of dodge!

you would be better off with gas tankless if gas is available in your area. electric tankless takes a LOT of electricity, and is not cost effective.

check into solar tax credits for solar
water heater. And for tankless gas w/h's

if you install an electric tank, look on the
box the w/h is shipped in. Energy Factor is what you are looking for. EF's are as high as .95, better insulated
but the lesser cost w/h's are in the .80 range. whirlpool
makes a .95.

check the department of natural resources website for
HERO program (home energy rebate option)
you should qualify. drop me an email if you don't understand the dnr site info.This program would help to
offset some of your upgrades.

keep in mind that with efficiency your cost is up front
and savings long term.

Heat pump would be a good savings for you, but if your
home has never had central you would have to install ductwork, system, and possibly upgrade electrical panel.
if no one in your area has experience in mini split install
you would have to factor that in your decision.

best of luck y'all!
kntryhuman
Original Author
15 years ago
I don't blame you. As soon as I'm old enough to retire, we're getting out of Louisiana.

The house had central air and heat but we tore all the ducts out. We would like to use the mini splits.

The house is over 106 years old so we have to gut the entire house, plumbing and electrical. We're starting from scratch.

We can get 30% rebate from the state on solar and 20% tax credit from the Feds. The water heater would cost us $8400 up front and $2000 after rebate & credit.

We're going to have propane. I think we're going to put in a propane tankless heater for now and try to do the solar in December. We can make a loan in December and pay it off in April when we file our taxes.

Do you know anything about the mini split systems?
kntryhuman
Original Author
15 years ago
Thanks for the explanation. We moved a 1300 sq ft 106+ year old house to Folsom and added another 575 sq ft. The addition is 10' ceilings, master bedroom, bath and laundry. The rest of the house is 8' ceilings, 2 small bdrms., 1 bath, dining, kitchen and den all open.

We are trying to do everything to get the lowest possible electric bills. We have Washington-St Tammany Electric.

We're seriously considering solar hot water and possibly electric. We will have a tankless water heater to start and use it as a back up.

The thing that's really confusing me is different companies saying they can't put mini splits because we would need 6. Then the other companies saying it's not a problem.

So if I understand correctly, the heat pump would be a better option.

What part of Louisiana are you in?

Thanks again.

I'm so confused over Mini-Splits, Central A/C and Heat Pumps

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I'm so confused over Mini-Splits, Central A/C and Heat Pumps

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