Hi Dana,
I used the words "central heating system" on purpose. Yes you could put in 1 mini split for every room or a 10 headed monster, but I was speaking in the context of 1 head to condition the whole house.

To your question I have the "M"RC (Michigan amended IRC) so the number may not be identical but in chapter 3 "Building Planning" R303 Light, Ventilation and Heating states the following-
R303.8
Required Heating
When the winter design temperature in Table R301.2(1) is below 60*F..........heating facilities capable of maintaining a minimum room temperature of 68F at a point 3 feet above the floor and 2 feet minimum from exterior walls in all habitable rooms............The installation of one or more portable space heaters shall not be used to achieve compliance with this section.
(and you thought I just made this stuff up ).
This is where I mentioned before that the innovators have specific requirements that have to be fullfilled for an inspector to sign off on their plan. So back to my first comment, I would be reluctant to believe a 1 headed split could meet those requirements in a code minimum house.

Is resistance baseboard in each room considered a "central heating system"?

I didn't think you made the stuff up, but thought (and still think) that there is no requirement for a "central heating system."

At 10 headed monster would have at least 8 grossly oversized heads running at way sub-optimal efficiency, as would a 10 individual mini-split solution. The notion that every room needs a heat emiitter to meet code is simply mistaken.

It's quite possible to meet the spec with point source heating by-design in new construction, by minimizing the heat loads of the doored off rooms and running the point source heat a few degrees above 68F. I've participated in a project where that was achieved a deep energy retrofit of an 1890s house in a location with a 99% outside design temp of +5F. The math isn't any different to do it on a house where the outside design temp of -15F, but you might end up having to spring for some pretty high performance windows if you like sweeping views.

Of course using radiant cove heaters & baseboards for temperature balance are cheaper to install than U0.12 windows, but it cuts into the net efficiency if not controlled by both occupancy sensor & thermostat. But that approach works just fine, and meets the letter & intent of code. With occupancy sensor control the room runs cool unless occupied, the thermostat puts an upper bound on it- it's cheap & easy to implement for those rooms where other factors keep you from getting the load down sufficiently. Radiant coves are more comfortable than baseboard in those instances because the cove heater raises the average radiant temp in the room before the room is up to temp, heating up the objects & occupants in the room first, rather than baseboard convectors which primarily heat the air, which takes more time before the comfort level is achieved.

With multi-story houses it's often possible to heat multiple floors from a single head with the help of convection, but it gets messy, and if using it for both heating & cooling the head is in the wrong location for single head cooling. It's getting to be pretty common to use one head per floor in high-R houses.

To meet the requirement in a code-min house north of zone 5 would require pretty small bedrooms, with minimalist code-min windows sized to meet the minimum legal egress. opening. But there's little point to building new houses to code min if it's a house you intend to live in:

Code minimums are the crummiest house you're legally allowed to build.

There are both comfort and long-term financial benefits to building considerably better than code min.

If you heat the main room to 88F, it's pretty easy to get that no-heat-source back bedroom to 68F. So apparently there is no code requirement for temperature variability.

Posted By jonr on 15 Mar 2014 05:51 PM
If you heat the main room to 88F, it's pretty easy to get that no-heat-source back bedroom to 68F. So apparently there is no code requirement for temperature variability.

:-) :-)

Point-source heating (or 2-3 point sources) in a 1950s house with the original windows might require different definitions of "comfort", but not in most mid-sized houses built to IRC 2012 levels.

But in new construction it's not tough to optimize for point source heating with just a bit of attention paid to the floor planning and individual room loads, even if you stick to IRC2012 code minimums on everything. If the plan is to go with ducted hot air from the get-go those details can be ignored, but the room-by-room temperature balance of those systems usually have some comfort issues of their own.

In better than code construction room-by-room temperature differences generally shrink, independently of the mechanical systems, which is a factor that most Net Zero or PassiveHouse builders exploit in order to cut the cost of the mechanical systems. Most of the high performance houses in my area (climate zone 5 & 6) are heated & cooled with 1-3 ductless heads, with NO resistance heating of any kind.

There are enough existence proofs out there at this point that it's worth considering for any new house design, even if it's nowhere near PassiveHouse levels for R/U. A high performance house buys more comfort than any mere central heating system can provide (with the possible exception of radiant floor heating.)

Posted By jonr on 15 Mar 2014 05:51 PM
If you heat the main room to 88F, it's pretty easy to get that no-heat-source back bedroom to 68F. So apparently there is no code requirement for temperature variability.

Very good point jonr ..... even in a new above average insulated home you would be forced to adjust the mini split to possible uncomfortable levels just to bring temperatures inline in the adjacent spaces with no mini split to a comfortable level. This is why mini splits can have serious comfort issues if you don't have a mini split in each space. If you did have a mini split in each space in most situations it would Not make any economic sense. This is why you use a central heating and cooling system to keep temperatures balanced through out the home.

For those which continue to pump up mini splits for newly constructed home are simply attempting to lower overall construction cost sacrificing the home owners comfort and among other things. If it is to be a cheap built home and sold as such, I suppose its OK. There may be very special circumstances where a architect may design a home around 1 to 4 mini splits which is really crazy and may work fairly well, but every persons needs are different and most all clients would not allow the architects design to revolve around freaken Mini Splits.

If the size of the ducts in a central air conditioning system are limiting a design, there is an option such as an high velocity central air system.

If it is to be a cheap built home and sold as such, I suppose its OK.

Actually, it's quite the opposite. The better the home is built, the easier it is to heat with ductless minis. You could do some interesting designs in which you had ductless minis heat a master bedroom suite and groups of two or three bedrooms at a time using a cul-de-sac arrangement. You could have a three bedroom home with a huge media room heated and cooled by a 4 head minisplit. The possibilities are endless.

Posted By ICFHybrid on 16 Mar 2014 02:29 AM

If it is to be a cheap built home and sold as such, I suppose its OK.

Actually, it's quite the opposite. The better the home is built, the easier it is to heat with ductless minis. You could do some interesting designs in which you had ductless minis heat a master bedroom suite and groups of two or three bedrooms at a time using a cul-de-sac arrangement. You could have a three bedroom home with a huge media room heated and cooled by a 4 head minisplit. The possibilities are endless.

How about add something useful to the thread ..... instead of just wasting database space and confusing readers.... Read the Subject of the thread will ya .....K

Another interesting aspect is the Asian view.  I don't think if they are using it in Asia, it means that it works well.  My family is from Taiwan, and I have been to Taiwan quite often, and I hate all of the minisplits.  It is unbearable cold or unbearably hot.  My relatives have them, the hotels have them, and it isn't very comfortable.  Maybe they are not working well or they have bad units or whatever, but they are used in Taiwan because they don't have any space for ducts, so they have to do something.  In my wife's sister's place, it is less than 1000 sq ft, and they have 4 minisplits, one for each bedroom, one for the office, and one for the common area, and if you try to use only one unit, it would be super freezing or super hot in the one room, and barely comfortable in the other room.  For us, we had it at an okay temperature in the bedroom, but then when you went to the common area, it was not comfortable, and you had to turn on the other unit.

ICF and Dana,
I have not suggested that the IRC requires a central heating system. A one headed mini would necessarily be "central". Obviously multiple electric baseboards or multiple anything would not be "central". This is a perfect example of scrutinizing individual words while missing the point which was- a single headed minisplit would not likely heat a code minimum house to required standards.
When you discuss envelope improvements Dana you exited a discussion of "code minimum", but this debate started when you commented ".....it's one of the most common solutions in Asia, where the average house isn't anywhere near IRC 2012 code min on thermal performance."
I am a fairly progressive minded HVAC guy without ego in a particular technology. I install what works best for my customer. In the real world (outside of these forums) people forsake heating, cooling and insulation for cosmetic things (i.e. marble counter tops) these homes would not be very comfortable with a minisplit or two. So while a "heat emitter in every room" may not be required for comfort in a higher performing house, it again may be demanded to meet code in a minimum house.

Jonr, you are correct and I have brought it up before, the code only discusses balance when you get into duct work and it asks for some way to regulate air flow.

it would be super freezing or super hot in the one room, and barely comfortable in the other room.

I think you might have other issues, possibly control problems, for example. I've never been with a mini split that overcontrolled a room like that unless it was told to. If you have to set one room too high or low in order to have another room habitable, you have problems with the building envelope. That's not the fault of the heating and cooling units. They do what you tell them. In fact, I haven't even begun to explore all the features on my units. For example, they will ramp rooms up or down depending upon occupancy, direct flows to various areas in the room and even communicate with other units to respond to unexpected need.

a single headed minisplit would not likely heat a code minimum house to required standards.

Joe, that's a red herring that you like to throw out. None of us have ever claimed that a single mini split is likely to do that in code minimum. Except, maybe, badger's buddy, Little Ricky there. He continues to hold that ductless minis are for cheap construction, completely ignoring the fact that they are, instead, excellently suited for quality construction.

If I were offered a "cost doesn't matter" hvac system, I'd pick low mass radiant heating and cooling. With enough ventilation (ie, small, low speed ducts) to make DOAS work well. At least one zone per room.

Something isn't quite right with these guys promoting mini splits as they do ..... they are obviously misleading readers about the reasons they are popular in certain country's and there capabilities in the American market etc.......

ba_icf you pretty much should have put the last nail in their coffin, but I'm sure they will come back to life as they are the vampires of society....

I'm unclear who "these guys" are, but if I'm on that list, I'm a fan of minisplits for one reason only: Having built many houses over forty years heated by wood, natural gas, propane and heating oil, I've never seen a heating and cooling source that is as inexpensive to buy and use, simple to install and works as well as these do. You are free to use whatever you want.

If I were offered a "cost doesn't matter" hvac system

What if cost DID matter?

they are obviously misleading readers about the reasons they are popular in certain country's and there capabilities in the American market

Feel free to detail exactly what you are talking about. If you can't come up with anything then you can skip down to the next item.

I was amused to go to one of your last company links and see the following as one of the "concerns" with ductless;

"Reduced overall indoor air circulation and increased humidity can lead to comfort and air quality problems"

Could you explain to us what that refers to, exactly?

Posted By ICFHybrid on 16 Mar 2014 07:50 PM

they are obviously misleading readers about the reasons they are popular in certain country's and there capabilities in the American market

Feel free to detail exactly what you are talking about. If you can't come up with anything then you can skip down to the next item.

I was amused to go to one of your last company links and see the following as one of the "concerns" with ductless;

"Reduced overall indoor air circulation and increased humidity can lead to comfort and air quality problems"

Could you explain to us what that refers to, exactly?

ICFHybrid

Veteran Member

Posts:2687

Based on the amount of time you have spent on this forum etc ....... and you cant figure out simple problems, I would bring serious doubt who you claim to be, and your capability to give anyone quality advice on this forum.

You alleged that I, and others, are misleading readers. You need to back that up with some substance. I'm a homeowner. Who are you?

Posted By ICFHybrid on 16 Mar 2014 10:38 AM

it would be super freezing or super hot in the one room, and barely comfortable in the other room.

I think you might have other issues, possibly control problems, for example. I've never been with a mini split that overcontrolled a room like that unless it was told to. If you have to set one room too high or low in order to have another room habitable, you have problems with the building envelope. That's not the fault of the heating and cooling units. They do what you tell them. In fact, I haven't even begun to explore all the features on my units. For example, they will ramp rooms up or down depending upon occupancy, direct flows to various areas in the room and even communicate with other units to respond to unexpected need.

That might be the case, but the reality is that everyone in Taiwan uses minisplits, and the temperature is not very good.  I am just visiting, so I am not trying to analyze why it isn't working.  Usually, the buildings have very little insulation.  They are usually made of concrete.   I just turn it on to a certain temperature, and it is usually not very comfortable.  Usually, it is still humid in the room, and the unit is blasting cold air.  All I know is that I don't like it, and they aren't doing what they are supposed to well.

It might not be the fault of the unit, but to say that they use them in Asia, so that means that they work is not valid.  They are used in Asia because it is their only option.  They can't use central A/C for most units.  They all live in condominiums made of concrete with no space for ducts.  To me, it is just a fancier window unit with a dedicated hole in the wall instead of using a window.

What is the advantage of minisplits versus window units?  It has even less plumbing and duct work.  It should be even cheaper.