Mini splits are great devices but they have their limitations in large houses with multiple rooms. The bathroom would get air when the door is open. The temperature could be several degrees above or below the the large living area.

How do you heat and cool the house now and do you want to install a mini split?

We are still framing. Before we started building I took plans to a couple of hvac companies and both thought it would be better to go with central air since we have space for the unit that is centrally located between all the rooms. But now both those companies and a 3rd company think it would be best to put the blower in the attic.

we had the blower in the attic in our last house and it really wasn't a good setup. when it wasn't blowing, we could feel warm air coming through the return air vent in the ceiling and when the ac did kick on, it blew hot air for several minutes before it felt cool. The only advantage is that it was quieter than one in a downstairs closet.

I asked about the mini splits when I was getting bids and they said the cost was about the same and for ac, the mini splits were more efficient. But for heat, they were not.

Husband is concerned that getting parts for repairs will be a problem. And someone else told us that condensation (lines?) was more of an issue with them.

Yes, maintenance headaches, long wait times for parts when they break, hot spots in the home where there is no room for the head to be mounted unless you put in a ceiling mounted cassette... but then it's just more and more equipment to maintain and replace when the system starts to go south.

Mini splits are best for small non-critical rooms. Unless you have 1 indoor head per outdoor condensing unit, then you have redundancy for when one of them goes down.

But if you have one unit outside with multiple heads indoors tied to the one unit outdoors there is no redundancy. If the system goes down it is most likely to take all the heads down with it... unless the problem is in one or two of the indoor heads.

The more equipment you have the more costly it is to maintain, repair and replace.

If you like the redundancy of having multiple systems so if one or two goes down you still have some cooling in a third system then that might not be all bad.

In the commercial realm they sometimes will put in over capacity of these systems for mission critical things that need to be cooled. Because the foot print is small they put in 2 equally sized units. 1 head and 1 outdoor unit for one side. 1 head and 1 outdoor unit for other side.

They run just one unit at a time and then monthly switch the units... the one that was running is shut down or turned way up as a back up protection if it gets too hot in mission critical room it kicks in as back up.

So they do have their space when you think about it. But in a residence I think it is rather limited unless the dwelling has a really small foot print.

We are in north central texas.

We have minisplit for our whole house. It was built without duct work and duct work could not be added. The way we handle the bathrooms is the master bath with vaulted ceilings and lots of window exposure, as well as sky lights, gets it's own unit. The other two bathrooms are central in the house (no exterior walls) so they just get what drifts in through their open doors from the central area of the house which is open with vaulted ceilings (we have the ceiling cassette there). If all your baths were on exterior walls and used regularly I would put a separate indoor unit in each as nothing is worse than getting out of the shower and sweating when you dry off. But our secondary baths are used more as powder rooms and keeping them at 74 or what ever the house is set at is fine.

For your application I would put in central air and ducts because they are cheaper and more available. Also more knowledge of people to work on them. If you are very picky about needing ice cold air in certain areas than mini-splits is a better way to go. If you had a large house that you only live in parts at a time then mini-split is better because the cool air falling from above gives an instantly cool feeling so you really only need to cool the area of the house your actually in. This doesn't sound like your application.

We have never had a problem with our system beyond some leaking refrigerant but we did ask after spare parts when we bought the system and were told they had easy access because these systems are very common in other areas of the world and the parts were in the distribution chain and available. We also have two outdoor units, one on each side of the house. So if one side were to not work, we could run the other and still be cool in at least part of the house. We really like that but your system size would likely be so small you wouldn't have two separate outdoor units.

1885 home isn't the same as homes built in the last 30 years. If you live around that many older homes then I can see how mini splits can fill a void that would be difficult for regular central air system.

The point is... 1885 homes are rare. So the opportunity only comes if you happen to live around a lot of older homes of this caliber.

The other part is location. If you live in some obscure location you will only find what is available in that area. Sometimes, your choices are few.

The attic is the worst place to install the air handler and duct work in my opinion. Try to avoid it even if it means giving some interior space.

Mike with 1348 square feet their choices are few as far as placement of equipment goes.

OP can you post floorplan of the house?

quite often you can fur down and keep ducts within conditioned

space. in my own small house I gave up half a closet for equipment

and installed ductwork in furdowns to serve all rooms.

austin air, my point is that mini splits are highly adaptable to many

situations. new construction, existing construction & old homes

can all be serviced by minisplit.

best of luck

This study address some of your questions about a limited number of units serving more than one room each in new construction. It is not your climate, but might offer some insight. If you are building a high efficiency structure, the efficiency of the equipment is not as important but mainly about comfort in this case.

Energy_rater_la, can you say which contractor for the NOLA work?

Long-Term Monitoring of

Mini-Split Ductless Heat

Pumps in the Northeast

K. Ueno and H. Loomis

Building Science Corporation

November

Well it's not also placement of the equipment it's also being able to service it and to be able to repair it or replace it (easily) again when the time comes. Cramming everything in a tight closet can cause more problems if you don't have the room to do it properly I wouldn't do it. Been there too many times... no room to do nothing except look at it.

People tend to like tall ceilings in the realm of home aesthetics and you also have to think about resale value of the home. Installing fur downs in home that doesn't already have them isn't advisable because you may take a hit on the price of the home or it could increase the difficulty in which to sell it when that time comes.

A solution should solve problems, not create new ones.

The mini split option could work in a home like this, but to cool / heat adequately would require probably 2 or 3 indoor heads, maybe more. That's a lot of equipment to maintain for such a small home.

I think you can give up 25 sq. feet for a utilities room (HVAC, hot water heater, etc). The chase for duct work can be hidden above kitchen cabinets are as the border of a tray ceiling. With a little planning the HVAC equipment can be efficient, easy to service, and look aesthetically good in my opinion. It does require some thought and planning which is what architects and engineers are paid to do.

Most folks who have strong dislike for installing the air handler in the attic are from Northern climates where good heating is a priority. However, in the South you can install well-insulated ducts in the attic and get very effective cooling, which is usually what you want. The heating capability will suffer with attic ducts because hot air rises, but in Southern climates the priority is usually cooling and humidity reduction, not heating.

One disadvantage of an attic A/C installation is that the layout of flexible ducting is often very messy, and they manage to take up a large part of the usable space in the attic. You also need good access to the equipment, preferably something like pull-down stairs in the garage so that the mess is kept out of the house. Some houses don't have space for a full-sized pull-down stairs.

Bruce

I wouldn't count on the bathrooms getting any direct air but since the area around the bathrooms will be cool the bathrooms should stay relatively cool with the air conditioning in the other rooms. You could install little breather air vents in the bathrooms connecting to other rooms and that will allow the warm air in the bathrooms to move towards the cooler air of the rest of the house. More times than not the space under the doors will do this for you but I would recommend bridge vents somewhere up high on the walls to connect the bathrooms to the other rooms to allow that "warm air that rises" to move outta the bathrooms.

Chicago Heating & Cooling

I have seven high-wall mount mini splits in my house. That meant that I was installing nothing direct in my bathrooms. I considered installing two of the minimally-ducted mini splits and using them for each bedroom/connected bath area. They are, however, more expensive and less efficient. I'd say the biggest problem is that they will not dry as well as if you have a duct in there and you may see quicker microbe growth on wet surfaces, particularly around the drains and shower curtains. At the time, the added expense made me turn away. With those units the shorter duct run obviously make placing the ducts indoors easier.

The biggest problem with outdoor ducts (attic and open crawl space) is that when they leak, they cause pressure differentials between inside and outside the envelope. There are some nice diagrams of how this happens on the web if you are having trouble visualizing it. Supply duct leaks turn your AHU into a power vent and warm, humid air gets drawn in anywhere there is a little gap. That can cause condensation when the air hits a cool surface, and mold, in addition to energy losses. It can also make it much more difficult to controlling humidity. Return duct losses in ducts outside the envelope pressurize the house, but consider where that air is coming from, nasty crawl or hot attic, perhaps? How much air does a typical new duct system leak? Maybe up to 5% is considered OK and it does not improve by itself as the system ages. Five percent is a big number for me. That is a lot of uncontrolled outdoor air coming in. Pressure differentials also occur due to imbalance between supply and return, but that is a different problem and less of an issue if the ducts are indoors.

You can have ducts near the ceiling and not have ducts in the attic. Homebuilders seem very difficult to move in terms of new practices for energy efficiency. It is no surprise that few of them have accepted the obvious fact that outdoor ducts should be avoided. One option, if you want to keep ducts in the attic is to seal and insulate the attic. That is increasingly done with old homes retrofitted with AC that have ducts up there. In old construction, it is often a lot easier than sealing up all the duct leaks and the leaks between the living space and the attic. In new construction, it has the disadvantage of adding HVAC load in that semi-conditioned space.

This is not to scale, and the proportions are off but this will give you an idea of the layout. The water heater is in the attic nearly over the downstairs shower.

We have 9 foot ceilings, and originally I thought we could have 8 foot ceilings in the grayed area for the ductwork and the blower unit in part of the space designated as safe room. The hvac companies didn't think that would work.

Eventually, we want to have a bathroom upstairs, over the left halfbath and shower room. Then have the rest of the space for office, ham shack, bunk beds, and sewing/quilting space. We do plan on a mini split up there. That is a few years down the road though.

Downstairs, the outer walls are about 10-12" with closed cell insulation in the metal outer walls, and foam board and batt insulation in the 2x6 framed walls. And yes, we will have HRV or ERV.

p.s. There are windows across the kitchen wall opposite and matching the living room windows, plus windows in the bedrooms - one window in the small bedroom and two windows in the larger one. There is also a door I forgot to add going from the kitchen into the larger bedroom.

Is R6 or R8 the definition of a well insulated duct? Would you use that amount of insulation for walls and attic floors? Yet for a duct it is about the best your are going to do. It really makes no sense when you consider the duct work is carrying air at 55-60 degrees, yet the conditioned space is being kept at 74-76 degrees.

But people are told the attic insulation should be R40, but R8 is fine for all the duct work that snakes around your hot attic.

It's supposed to be really hot here today in Katy, Tx. If I think about this later on this afternoon I will take a picture showing plenum temp with system running and system off.

I know I have a problem with this house I just moved into late last year. The thing is knowing you have a problem and willing to do what is necessary to fix it. You can't just ignore the attic just because you have the room necessary to relocate the system within the conditioned space of the home. If you don't fix ventilation problems your system will still not perform well. Additionally you still need room to run the duct work within the envelope as well. That isn't a viable option for an older home.

If you have an older home, you really only have one choice in my professional opinion.

Attic installations can work. R8 ducts in the attic are perfectly fine provided that the attic is well ventilated. I am going to be fixing these issues within the next 6 months or so at this house I currently live at.

The previous house I lived in is now a rental. I asked my tenant what her light bill was for May she said $17. Said she runs the system at 74.

My bill at this house was $91. This house is larger but I typically only cool maybe 1/3 of it most days. I can clearly see the difference from this house to the last house, I have a good idea where the problems are. The system is a 2 speed system over here, but likely 14 SEER at best. It's only a temporary system as this house needs lots of work still. (I tend to get bored a lot in my off season)

I will be documenting these things on my YouTube channel over the next year or so. You can subscribe to my channel here.

There are videos there that show what my utilities were when I lived there as well as how I ran that system over there.

Here's a picture of the attic of my previous home

I have more pictures in the way of problem areas for this house. If this gets to be too much for this thread and people are interested in this subject let me know I will start a new thread.

I will say this... the attic temp is misleading because it's air temp. If I use an infrared thermometer off various targets it's typically 130 or so. The idea is you have to get this temperature down thru natural means because right now this is robbing me big time.

I know that it was not your intention, but with your air vs surface temperatures, you've demonstrated why attic ventilation can't really have much of an impact on keeping the house cool. When the sun is shining, Shingles absorb energy that is transmitted through the roof sheathing by conduction and then radiates it to other surfaces in the attic. The primary means of heat transfer from the roof to other parts of the attic is radiation. It would be difficult, or impossible, to flow enough air through an attic to have a significant impact on heat gain in the dwelling space.

But it does... That little v in HvAC stands for ventilation. It's not there by accident.

Here's some more info on it. The importance of attic ventilation

That is an interesting piece from an historical
standpoint. The approach and attitude are appropriate for leaky homes
built without central heat and no mechanical cooling or ventilation. I am
thinking 1940s at the latest. It is clearly biased towards cool, drier Northern
climates where vented attics may still have some merit. We are addressing a predominantly hot, humid
environment unless I missed my guess about North Central TX. (Are ice dams a common problem in the OP’s
location?) Today is it generally recognized that vented attics with ducts in
them in hot humid climates are not a good idea. One building expert went as far
as to write. “Venting attics in the South was dreamed up by some disgruntled
Yankee pissed about the Civil War and wanting to get even.”

The Asphalt Roofing
Manufacturers Association, which apparently produced the linked article, has a history
of suspicion of unvented attics with insulated roof decks. Even though the increased temperature of the
shingles in inconsequential, and will have little or no effect on shingle life
they are more worried about their precious shingles than the utility bills paid
by the people under them. They present no data to support their position
because they don’t have any.

Well there's more than one way to look at it like anything else you want to look at.

I realize the document comes from the shingle industry which is merely to say that no one else cares to think about the effect of an improperly vented attic. If not for my previous home and the proof it provides in the way of comfort, the way of low utility bills and the differences in temperature I've personally seen from one attic to another.

It's not hard to imagine a 140 degree plus attic versus a 100 degree attic and the effects of load on the structure these two different temps will have. My case is not as bad as some I have been in. But if I can reduce my attic temp of 114 degrees on a hot day (95 or so OAT) a mere 10 degrees, it will have an overwhelming impact on performance of the AC system.

(The money it costs to operate month in month out. Many argue saying a heat load calculation should be performed... why not fix problems related to heat load of a structure. The canary in coal mine if you will...)

Whether it's a good idea or not to put HVAC systems in an attic isn't an argument I am going to win in a house that was built in the late 70's. The cost to put it in doors is not only impractical it would be far too costly.

Homes being built today in this region are still being built with HVAC systems and duct work in the attic. There is nothing to suggest it can't work. Remember I have proven it can work with my previous home.

I will also add my previous home has no radiant barrier nothing. No paint, no preformed roof deck with radiant barrier backing. The attic ventilation (natural) over there is about as good as it gets and there are no thermal breaks unlike the house I am in now.... I've attached a few more sets of pictures below.

There are more than one way to reduce attic temperature. A very common way is to suck the air out with power vents. They were a real big fad for a while, remember? Much of the time, the replacement air came from the living space, heck of a way to cool an attic.

What is an “improperly insulated attic”? The thinking of the home construction industry is totally upside down and it is hard to turn a group like that around and make them see things right. We’ve had widespread mechanical cooling in homes for over 50 years and the industry has not been able to catch up to that yet. The fact is that an attic in my climate (South coast) with insulation between the attic and house IS improperly insulated. The insulation belongs at the roof line. That is certainly true with ducts in there and may be true even without ducts in there.

What will the impact of reducing the air temp in your attic by 10 degrees? Again, most of the heat transfer is radiative. If calculated, I think we will be underwhelmed and most of the effect will be on losses via the ducts. If that is true, move the ducts inside the insulation rather than insulating between the house and the ducts.

To tough (expensive) to move the ducts? That is why building experts are encouraging folks in that position to seal the attic up and insulate at the roof deck. That is second best, but cost-effective if you have to relay on construction professionals. If a homeowner is willing to spend a few days or weeks in the attic sealing air leaks, and sealing duct leaks, you can do better than sealing the attic and insulating at the roof line. How many of us can do that?

With a sealed attic containing ducts, the duct leaks have a minimal effect because the attic is coupled to the living space, and you only have to insulate the ducts enough to prevent condensation. A cool metal roof might be a good investment if the owner is going to be there for a couple of decades.

Older homes tend to have a lot of openings through the ceiling. It is frequently less trouble to insulate at the roof line than try to fix a mess like you will find between attic and living space. Most people won’t hesitate to punch holes in their own, or ceilings of others, the cable guy, the homeowner, electricians,… Hardly anyone with punch a hole through an insulated roof deck, for obvious reasons. When it rains, it will pour.

Power attic fans have a bad reputation because most are improperly installed.

Insulating the roof deck is much more expensive than insulating the attic floor. Plus there is a greater chance of improper installation. It is not needed if the HVAC and duct work are installed inside the conditioned space.

I'd go further and say that almost any power vent is improperly installed. That's because proper ventilation means no power vent. I suppose there may be special cases where it is not possible to vent well without power in some unusually-designed attic.

Zone 4 hit 90 degrees yesterday evening... 10 degrees less in attic would do what again? (It can't hurt, unless I fall thru the ceiling while fixing these problems.)

Certainly there are more issues for this zone than just attic ventilation and insulation... just so you know I am looking at the whole picture.

Insulating the roof deck. Nope. If the roof develops a leak you're talking one hell of a mess. Texas is known for violent storms... IE: Hail, followed by torrential rain down pours and then brimstone heat.

Powered vents: Nope. Natural ventilation is the best way.

Certainly design of the house can play into how well or not so well the attic can be ventilated. Stay tuned to that old 'Hot Channel' we're going to find out... God, willing.

I am not one to back away from a challenge. (Putting HVAC inside the envelope is pointless when I know (previous home) works excellent... low utility bills and crisp cool air the minute you walk into that house. You can't escape that feeling in this fish bowl weather. (IE: high humidity).

Major redesign of the HVAC system / where it's located as well as duct work is costly. You have to not only move duct work, you also have to move electrical or gas connections if it's gas system, duct boots are all in ceiling of rooms all ducts are in attic. How are you going to supply rooms? Pointless and not worth the expense to attempt to put the whole HVAC system + duct work within the structure envelope. If you only put HVAC in envelope and duct work in attic you wasted your money relocating equipment only and when system breaks down it makes repairs that much more complicated and costly. (crammed in a closet).

PS: there are no basements here. 99% of all homes are on concrete slabs.

Moving the HVAC in an existing house out of the attic is not practical. It is an option for new builds.

i feel the power vent has the most benefit at night when the outside air temperature drops 20-30 degrees.

A summary of my thoughts on this is that in new construction, ducts inside and same for furnace/AHU, the whole system. In the sad situation where the homeowner has a poorly insulated attic with a lot of leaks to the living space, it is very often most beneficial to seal the attic and spray insulate the roof deck. Yes, in a DIY situation, it can be less expensive to find and seal the leaks and re-insulate the ceiling, but if you have to pay someone to do it, not so much, and you still have the downstream problems associated with adding more holes to run utilities and such. Insulating at the roofline does have the drawback of added heat exchange compared to the ceiling due to increased surface area.

All roofs leak, hail or not. Retrofitting homes with high density spray foam under the deck greatly strengthens them to wind damage even weeks after wetting from leak damage. There are problems with this type of insulation that need to be worked out, but it is not moisture from without, but within.

Spray foam under roof commentary

Taken from spray foam under roof commentary........

"Ready for this… here it comes…
roofs leak. They always have. They always will. Sometime you see the leak,
sometimes you don’t. This is true regardless of what system you use. There is
no greater risk of roof damage with SPF, regardless of type, under a roof deck
when exposed to a leak than the risk compared to structural insulated panels (SIPs)
or typical commercial compact flat roofs. We can build with multiple layers of insulation
and membranes and decking, and somehow we manage to deal with roof leaks. It is
not the end of the world. SPF is not a greater risk under a roof deck than the
risk associated with commercial compact flat roofs with multiple layers of
insulation sandwiched between roof membranes and metal and wood structural
decks. SPF is not a greater risk under a roof deck than the risk associated
with SIPs."

Realize when I say roof leaks I am talking about roof leaks from a roof deck with no
insulation of any kind (no panels - nothing) They are comparing their foam to SIPs. I am talking about just OSB decking no panels no insulation of any kind on roof deck. If there is a roof leak you will see it in a Katy, Tx rain storm. I am talking about a sloped roof. Realize Houston total rainfall is comparable to places like Oregon. Except the rain fall in Houston
area tends to occur in big and some times long rain storms rather than smaller rain storms all year long.

Taken from spray foam under roof commentary........

"Ready for something else? Here it
comes… sloping roofs are less of a risk than flat roofs. Wow. This gravity
thing is a big deal. With a sloping roof you have less hydrostatic
pressure and if you do have a leak it is more likely to be seen inside
regardless of roof type. Note the “regardless of roof type” comment. Built up
compact, SIP, SPS… it does not matter."

Sure but once that roof is saturated for hours and hours long of rain fall, if there is a leak
the water will find it. If the roof deck is insulated you will have to rip all
that insulation out to find where the leak is. Gravity works against you here. That
is the point is it not? The water travels how far down the insulation until at
some weak point in the insulated roof deck it starts dripping. Yeah that's
going to cost you. I can't make this point any more clear to you.

You must realize the people selling this product are doing what they can to keep
selling it. It creates more problems than it cures and it's costly. If you're made of money then you probably have other problems dividing your attention right now.

All across the nation if you've ever ridden on an air plane or flown in a helicopter... look at the top of commercial flat roofs. What do you see? building after building?

I'll tell you what I see.... HVAC package units sitting in the out door weather. In some cases even the duct work sits on the roofs covered in what is commonly referred to as a 'dog house' to protect the ducts from the weather.

Everybody and their brother has something to sell you, no? I don't know maybe you are trying to sell it to me? (good luck, I know better) They all claim they have the best thing since sliced bread. I am here to tell you it's not what it's cracked up to be.

(I have been in rental homes, I have been in home owner homes for over 22 years now... I have personally found roof leaks on more than one occasion, not only in homes of others... but also my own. I am not a roofer by the way.... For those reasons, I will never agree with mentality of insulating a roof deck. It doesn't hold water. After what I have pointed out, if you choose to continue to think it's a better way you may never have a problem with it. Roofs in various parts of the country can last what? 30 years? By the time people start complaining of roof leaks and big messes with an insulated roof deck you could retire huh? )