Central air vs. mini split ?

[John Albert]

Hello all -

I may be buying a house before too long, and a few questions about installing air conditioning into a home that lacks it. House will be ranch-style, 1600-1900 sq. ft. I have no house in particular picked out yet, but some I'm interested would be fine -- EXCEPT for the fact that they were not built with air conditioning.

I'm wondering about the pros/cons of installing a "mini split" system (with multiple "room units" or perhaps more than one mini split unit), vis-a-vis going for central air...?

Just from casual browsing, it looks like mini split would be considerably cheaper and easier to install than a full central air system with ducting, etc. (the latter probably involving a LOT of wall/floor work as well).

Is central air worth paying the extra $$$ and installation work? Or can mini split do as good a job, have equal reliability, etc.?

I'm also wondering if pre-existing ducting in some homes that have either oil or gas hot air, could also be used with a central air system?

Actually, if I found the right place with pre-existing ducting, I might even consider going to a full geothermal system. But that's a different topic.

Thanks,

- John

[trader4]

It depends on the house, what it already has, and how easy or hard it is to run ducts. If the house has forced air heating, then generally no new ducts are required. If it has hot water heat, then a lot of ducts are required. How much work that is depends on the layout of the house, ie basement, crawlspace, etc.

MS is good for areas. One room or a few rooms. If you need and want to cool the whole house, as most people do, then central is what's needed. MS or even window AC can be used as a supplement to central AC. If you have a room that has a lot of sun exposure, isn't being cooled adequately by central, or a room you spend a lot of time it, etc.

But if you're in an area with periods of high humidity, nothing beats central air.

Yes, they always are. Another option you should look at is the new high velocity systems. They use air under pressure through like 1.5" hoses to deliver it. They are more expensive, but might be viable for a retrofit, because they use those hoses, not ducts.

Yes, it sure is.

[gfretwell]

I have been researching the same thing myself. If you already have forced air you might be able to use the existing duct work by adding A/C registers in the ceiling but it all depends on how the ducts are run. In a retro fit, if you need extensive duct work a minisplit ends up being competitive or even cheaper. Then the question becomes, how many condenser do you want. There are multi head systems but they end up being almost as expensive as using a one to one setup with multiple condensers and heads.

The first thing you have to do is create a scope of work on the particular house to see what is necessary to do the install.

Equipment alone

2400 BTU 3 head Fujitsu Mini Split $3400 3600 BTU 3 head Fujitsu Mini Split $4550 3600 BTU Trane 16 seer central (air handler and condenser) $3980 with a $585 rebate from FPL.

That does not include duct work, copper or labor.

[Lee B]

I don't have any technical knowledge about this. I can say that about 12 years ago, I had central AC added to my 1950s row house (basement plus 2 stories). The house had forced hot air, which the local utilities company used. At the time they warned me that the outcome would be that it would cool the 1st floor living area fine, but not so much the top floor. They were right, although it was definitely an improvement over what it had been like with no AC. I forget now how expensive it was, but they used the existing duct work and fan etc which helped to defray the costs.

Now I'm in a small 2 bedroom ranch that has central air. I'm almost positive that was an add-on as well since it's also a 1950's house. It does cool the house well, presumably because it's not trying to push air uphill. There is one floor vent in a bedroom that looks out of place and a return up on a hall wall, so they may have run some additional duct work, but I don't know.

FWIW, one of the houses that I looked at in this area (most of the houses in this neighborhood are identical) had been renovated and they'd put the AC (or maybe it was a heat pump?) in the attic. That seemed to work fairly well from what I could tell at the open house.

[(PeteCresswell)]

Per [e-mail]:

My parent's place had a system where the air was delivered through what looked tb 1.5 or 2" hoses. It was a retrofit.

I found the noise to be irritating enough that I would never have one installed in a house that I had to live in.

We recently re-did our system so that it has three zones: bedrooms, living room/kitchen, and rec room.

If I ever built a house, I would have a zone for each room and doors to enforce the zones.

My thinking is that hard times are coming fuel cost-wise and more zones would allow one to cut back heating/cooling to just a couple of rooms - or even just one - if the need arose.

[The Daring Dufas]

You beat me to it. Johnstone Supply was carrying the units but all I see on their site are the parts for it. O_o

TDD

[krw]

Unless the system were designed like a mini-split, I doubt you'd ever pay back the initial cost. I do shut vents off to rooms we're not using and have the upstairs unit on a "Nest" (we don't use the upstairs rooms much in the summer).

[clare]

Forced air systems are MADE for central air, and vice versa.

The ducting will be optimized for one or the other, but useable for both - or possibly a compromise for both - but it works.

[clare]

They can drive you nuts - some are terribly LOUD, at an irritating frquency.

[The Daring Dufas]

The units remind me of the AC systems on passenger planes. ^_^

TDD

[krw]

Or the Motel-sex.

[Stormin Mormon]

I worked for several years, helping a friend with his HVAC business. We installed central AC into systems which had been designed for heat only. Very possible, and we did a bunch of them. Of course, the HVAC folks in your area may or may not offer this service. The boss didn't discuss prices with me, so I'm not sure what this all costs.

. Christ> Hello all -

[Ed Pawlowski]

There is no one answer. Central air can be installed in any house. It comes down to cost. If no ducts, you can run them, often trough attic spaces or from the basement, through closets, etc. Since you are looking at ranch stile, it may even be possible to install the evaporator and blower in the attic.

As for using existing duct work, that depends on the layout and size. It may be possible, but it may have severe design limits too. That will vary with each house.

Mini splits usually are easier to install. They also have the advantage of being operated in just the zones you want to cool if you have a portion of the house not occupied. The practicality will be determined by the layout of the house.

Keep an open mind until you finally find your dream house and have a couple of HVAC contractors look at it.

Better yet, build your own energy efficient house and install the geothermal right from the start. Use ICF construction and it will be quiet and strong.

[trader4]

I've only seen one in operation. It was during an open house for a house being sold. It was an old colonial style house and it was a hot summer day. The house was nice and cool, air was coming out of the vents and I did not notice any noise. But, can't say what level it was operating at either. They could have had it cranking before the open house, and cut it way back during, etc.

My understanding is they have a design with special outlets that reduce the noise that you would expect. But how well that works probably varies from one manufacturer to the next. I would definitely want to see a few of the ones I was considering before having it installed.

I don't know about a zone for each room, but I agree that it's shocking that zoned systems, even doing just two, are not common on a single system. You do see a lot of new big two story homes with two zones via two separate systems, one in the basement, one in the attic.

Not only that, but increased comfort, as it can be balanced automatically. I think the big problem here is who pays for all this? Easiest and cheapest time to install that kind of system is during construction. But most homes are being built by spec builders, not homeowners. So, the builder may say to himself, if I sink an extra $5K into this, will the house sell for $10K, $15K more. Will a prospective buyer really care, etc.

I see this kind of thing going on here in NJ all the time. Builders are building $700K - $1mil houses and doing lots of cheap things that are a long way from shelling out extra money for fancier HVAC. If I were a builder, I'd try doing some enhancements and then making that a feature that distinguishes me from the competition. Basically, yeah my house sells for $50K more, but look at x, y, and z, what I'm giving you. A good place to start would be bathroom fans. In those houses referenced about, they all use the cheapest, noisiest fan available. For just $30 more, you could get one that was much quieter. Then when you're selling it show that to the clients.

[trader4]

Agree with your overall points. But that cost for the 36K BTU central eqpt is way high. It might be Tranes price, but you can get good eqpt from a company like Rheem for more like $2500. I bought a Rheem 5 ton/60K btu a couple years ago for about that price. It was 14.5 Seer though. Don't know what the price curves look like today, but 2 years ago, it didn't make sense to shell out the extra money for higher seer, the payback was just too long. That was for me here in NJ. If you're in AZ or FL, it could be different.

[trader4]

Even in two story houses that had AC installed when built, it's typical for the upper story to be warmer. Around here, NJ, they are going to two systems for larger houses now. One in the basement, one in the attic. That can help solve it, but also the system in the attic brings it's own problems. In my experience, a difference of two or three degrees in a house with a single system isn't unusual.

This stuff isn't rocket science and you would think installers today could do a better job, but it is what it is.

I forget now how expensive it was, but

[trader4]

You're in CT I think? Are you seeing geothermal being economically advantageous there? I'm not up on the latest prices, but I haven't seen anything that changes what it needs, eg wells drilled, etc that make it cost a whole lot of money. I guess if nat gas isn't available, and oil is the other choice, then maybe it could make sense. There is one system installed here in my neighborhood. But with nat gas available there, it makes no sense to me.

[(PeteCresswell)]

Per [e-mail]:

Considering that the cost to zone our rec room was well over a grand, I'd have to agree with that.

In retrospect, now that I know what a mini-split is, we would have been better served by installing same for the rec room - which is at ground level. I would think that the install would have been about as simple as such installs get.

[gfretwell]

Are you talking about an air handler or just dropping an "A" coil in an existing furnace? Big price difference.

[trader4]

Only drawback is that the minisplit would have cost 2 to 3X.