I would avoid the mini split plan. That sounds like a large structure and mini splits require a lot of specialized maintenance not to mention a lot of equipment to properly cover large structures. The mini splits, once they start failing (at the latest 10 years into owning this home depending on use and other factors) will probably bankrupt you.

Trying to put in a ducted system later will be very costly and a big mess. You are right to question this contractor's plan. Good for you.

Thank you for your comments. Are you familiar with the Unico small duct system and might that help solve the problem? It's a 4 level house but total square footage is only 2420 or so. Top level is only 265 (office). Bottom level is daylight basement.

A mini split could be a good solution for the top level office. Being that it is the top level and may have computers and monitors which generate heat, the heating load will be high compared to the area. It also gives you an independent control for that level. You would also be able to set back the temperature when you are not using the office to save energy costs.

As for the rest of the house I would sit down with the architect to figure out how the duct work can be run for the other three levels. He may have to create a chase to run the main duct. I would look into this as one of your options.

Thanks very much Mike. Good advice.

If you go with some sort of exotic type system (exotic meaning rare) and the builder blows away like they often do... who then are you going to use to service this equipment?

While you don't think 2400 is all that large it is to a mini split. Most mini splits are designed to cool one room. So you would need a head in every room in your house.

Now lets say you have a small bathroom, how uncomfortable is that going to be?

Are you going to try to cram a mini split in each bathroom too?

Certainly their are mini split systems that have ducted options... BUT: I thought the whole reason to going to mini split was to not have ANY DUCTS.

Because this is a new build you have your work cut out for you. Builders are builders... they are typically on the hook for 1 year after that you typically call someone like me to pick up the pieces and tell you all the bad news.

If you think ducting is a nightmare now, you're in for a rude awakening in 8 years or less after this home is built.

Austin, I'm agreeing with you. I don't think a mini-split is appropriate for the entire home. I'm not sure why the hvac contractor recommended that. I am owner/builder on this project. I will choose the hvac contractor and system. I think I need to get back with the architect and discuss a ducting plan for this house to make sure there is enough room for the ducts.

Have you ever heard of Unico? They have mini-ducts that fit in tighter areas. Not sure about quality and effectiveness.

Unico

They make duct work for what is called 'high velocity' ducted systems. This ducting will not work with normal standard HVAC system. A high velocity system would be required. That is why I called it 'exotic'. I have never seen one in operation in over 20 years of being in this profession. I have 'heard' about them albeit very loosely.

High velocity means the air moves at a faster rate... it has to because this system has to make up for 'volume loss' from the standard ducted way of doing things.

If a contractor doesn't understand or know this technology it will mean whistling and all kinds of air noise, which is likely to lead to full destruction of the system over time.

The duct system are the lungs of the system... a HVAC system won't go very far with bad lungs. You can not mix and match these kinds of systems... it will not work under heavy AC or heating loads.

Thank you Austin. Unico claims 500,000 installations. I'd much rather have a common conventional system. I'm still not clear why my house plan is considered a nightmare. It has a dedicated plenum extending through all the levels. I understand that you have to run ducts from the plenum to the rooms but aren't the clearances fairly standard for 2x6 construction? Maybe my architect didn't include soffits?

Sure they could have that many in a small area within the country, but it is still a specialized segment that I have never seen personally in the field. I have seen a lot over 22 years, but this was not one of them. LOL.

If it were me I would probably put in 1 multi stage HVAC system, possibly inverter (full variable compressor) and then zone at a minimum each floor. Knowing me I might even zone a few individual rooms for even better control. (like the master suite as an example)

As far as ducting goes, I would have made sure the architect that I hired understood my intentions of cooling and heating this structure up front. I assume that this step is probably too late.

I don't do new builds and I know that there are a lot of companies that don't do new builds either. So your search to find other options is going to be a long hard road.

I haven't broken ground yet so it's not too late to address hvac in the building plans. Lots of companies don't do new builds because they aren't qualified to do so. It's more technical and requires greater expertise. Whenever I see a company that does hvac, plumbing, duct cleaning and repairs I know they are usually a bunch of hacks.

I can see that it would be a nightmare unless you've built in 2+ feet between floors like a commercial building. Think about it - if the space between the floors is a "normal" joist height, where are the ducts going to run? parallel to all the joists? probably not, so that means soffits. Perhaps you can put in the floor on the lowest level (but probably not if that's on a slab) so then that's a dropped ceiling of soffit, then you can use that for the floor for the "main" floor, and then where do the ducts go for floors 3/4? between them? or up in the attic for the 4th floor?

Lots of companies don't do new builds because they are not qualified to do so.

In Texas all you need is someone with a HVAC license. That would be me. However, new construction has low margins. The only way I am successful with that is to hire a bunch of unskilled labor to install everything. (I would make all the money, the workers would make a pittance and the home owner would curse my name --- at some point during a heat wave in their new home.) --- if you want to know the real reason I don't do new construction... I only have one 'real' name it's not made up. A rare thing these days.

Finding this unskilled labor is harder and harder all the time. No one willing to work for $10 an hour and those that are... God help you.

What you say about them being a bunch of hacks is true.... just not necessarily in the right order.

If you haven't broken ground, then you should run back and see how you can address the HVAC issue. The last thing you want is to build a new home and it not live up to all the hype.

I would think the second floor joists would be a minimum of 2x10 lumber on 16 in centers. That gives you sufficient space to run duct work parallel to the joists. With some planning it can be done. Most homes where I live are have two stories with the HVAC equipment in the basement. Even if the second floor has a separate system it is typically installed in the basement like it is in my house.

Thank you Mike. The joists are 2x14 on 12 inch centers. There is a mechanical room in the basement with a plenum extending to all levels of the home. There is plenty of room for soffits in the basement. It seems like a conventional system for the basement and main level would be fairly simple. Maybe a mini split for the upper levels? Southern California is very mild for most of the year.

Thanks Mike. I'll work with the architect and find a good hvac designer. I've come to learn that the hvac industry is full of incompetent shysters (at least in Southern California).

My HVAC contractor showed me a 6,000 sf high-end home with a high-velocity system that a buyer had specifically requested from the builder. The buyer never closed and my guy's task was to try and figure out a way to reduce the windstorms coming from the ducts. So if you're going that route you might want to check out a home with such a system and see if it's OK with you.

I've seen high velocity systems used when retrofitting a historical building with A/C, especially when they don't want to tear up too much of the old construction. The ducts are much easier to snake into smaller spaces. However, with new construction that is still in the planning stage I assume that traditional ducts should be included in the architect's planning for utilities.

I do have to say that keeping hot/cold air stratification comfortable may be challenging if there are really 4 distinct levels. In my area a single HVAC unit has difficulty keeping consistent temps in a simple 2 story house, and having the upstairs hotter than the downstairs is a very common complaint. You may need at least two A/C systems, or some very smart zoning to keep temperatures consistent across levels.

Bruce

There are many options for
mini-split indoor units. Some requiring short duct runs and others with
no duct at all. You can also ask your contractor about additional options
like floor-mounted or ceiling recessed units.

Thank you Mitsubishi. What is the duct diameter for the mini-split ducted units including the return air?