I am building an open plan 2 story daylight basement house in zone 3, foothills of N Ca. Calculated BTU/hr is 20,000; R21-R26, R50 ceiling. I will have 2 mini-splits, ductless, 1 up and 1 down. Downstairs services a family room and 2 bedrooms. Bdrm-FR-bdrm layout. The county says a ductless mini can only provide heat to one room and one other through a door. If the total BTU output of lower unit is well over needs, why wouldn't the heat go south as well as north from the family room? How do I point out and convince this bureaucrat? Or do I just add a baseboard to meet his rules and then never turn it on?

You could try showing the official a room-by-room heat loss plan which shows that the odd room out won't be too cold.

Or, you could just add another head to the system to satisfy the wonk.

> just add a baseboard to meet his rules and then never turn it on?

If you can't convince him, that sounds like a cost effective solution. But have you done the calcs to show that a bedroom with a closed door will be adequately heated from an adjacent room on design day?

I am a code official. There are requirements often not met by minisplits as the code is not up to speed on high performance envelopes. You have run into the requirement that calls for conditioning of an "occupied space". If you can convince the inspector that the room is a closet, then there is no heating requirement. If you can't then the baseboard at $50 is a cheap remedy and as a bonus, back-up heat if your minisplit goes down.

What jonr said. The county is clearly wrong, but it's sometimes cheaper to just appease them- pissing matches never end well when they have the power of signoff on the certificate of occupancy. (I had to replace my circa 1923 toilet to move a drain to accommodate the placement of my new boiler and install a drainwater heat exchanger. There was no rationale given for that inspector mandate, but I really wanted to have the heat & hot water up & running given that it was November.)

But if you ever think you WOULD use them (either as backup, or during the cold-snap of the century), cove heaters mounted at the top of the wall are more comfortable at lower room temps. A 450W (~1500 BTU/hr) cove heater is under $125, delivered, and 600W (~2000 BTU/hr) units are under $150. I suspect the bedroom's design heat load is lower than that.

Adding oversized heads for the rooms to accomodate this is expensive and also leads to lower operating efficiency. Mini-ducted solutions that split the the output but sized for the pairs of rooms would be better individual oversized heads. The smallest ductless heads out there are in the 7000BTU/hr range, almost certainly 3x-4x oversized for the bedroom. Anything over 1.5x oversizing for the peak load comes with an efficiency hit.

As ductless systems and low-load homes become more common local building codes will eventually adapt. Code mandates for having specific heating/cooling to every room originated during the days of uninsulated balloon framing and single-pane windows, with heat loads 3-5x those seen in current code-min. Point source heating in the bad old days was both a comfort problem and fire hazard, as people stoked the coal stove to where the thing was glowing red to keep the remote rooms warm enough. Clearly this is not that kind of house.

When calculating the heat load of the bedrooms, don't forget to include the 250 BTU/hr per sleeping human in the room, which can cover a real fraction of the room's heat load in a house with design heat load of 20K, especially if the window area is smallish.

"What jonr said. The county is clearly wrong, but it's sometimes cheaper to just appease them- pissing matches never end well when they have the power of signoff on the certificate of occupancy."

See that's the thing, it is often not the individual or the local inspection authority. We just choose to blame the messenger. Codes are in force, and those who choose to color outside the lines need the blessing of the inspector. Admittedly the lines are about 10 years behind in high performing envelopes with high performance heating equipment, but the individual inspector has no more power to change the rules than the traffic cop who thinks 55 is too slow in a particular speed zone.

Both are very much aware of the letigious nature of our society however and the patrolman doesnt want to get sued because he let a speeder go that later caused an accident, nor does the inspector want to be sued by a subsequent homeowner who doesn't like minor disparite temperatures from room to room when code had very clear guidelines.

It is easier to think of inspectors as ignorant or behind the times, by and large we simply enforce the rules we are responsible for (and few of us enforce all of them). It also may suprise some of you to hear that not everyone thinks an unducted centrally located minisplit is the best way to heat partitioned space.

Note I didn't say the inspector was wrong, just the county, and on the technical merits. I totally get the inspector's duty & liability issues- he has a job to do, and where the county codes are explicit, it's not as if he has the flexibility to grant at waiver without a review, which just adds time, and the lost time likely adds an expense in excess of the installed cost of an electric baseboard or cove heater.

In the case of being told to replace the toilet to obtain a sign-off on moving the drain a couple of feet, I looked but could not find anything in my city or state codes that mandated relacing it with a low flush toiled unless I was reconfiguring the bathroom, which I was not. In this instance it seemed to be the personal whim of that individual inspector. I have no insight as to what else had been going on within the building department that would have pushed him to push me to change it, but it certainly wasn't worth wasting time or breath arguing about. There are more than enough sub-current-code features grandfathered into this now 90 year old house than mere plumbing fixtures, and he could have been pickier about other aspects of the boiler installation that got in without comment, but that I anticipated at least some minor discussion about (such as whether the strip of elevated concrete next to the driveway where the venting terminated constituted a walkway, which could have precluded venting the boiler there under the code.)

I found it a bit odd that he didn't also insist on replacing the toilet in the upstairs bath, using the same drain as the first-floor bath but wasn't about to ask, eh? ;-) Only the main-floor toilet was updated. The other eventually will get replaced as I update the upstairs bath (a project only recently started.)

On the few occasions I've read code for this issue, it says that each space has to be adequately conditioned. Sometimes it says that the heating or cooling facilities have to maintain a certain temperature in each room. It doesn't say that there has to be a DEDICATED piece of equipment or a SEPARATE outlet IN each space to do the conditioning.


Once you have spent some time in a properly insulated and sealed shell, it begins to sink in how this can work.

Thanks for the replies. I suspected that fighting city hall would be harder than a work around. The curious part is that thy seem to be ok with heat passing through one door to heat an adjacent room. Family room through door to bedroom A. If so, why not family room through door to bedroom B? Same design, other direction. BTU production by minisplit is more than sufficient.

McFish,
Again it is not whether BTU's are sufficient it is wheter they will be communicated to an occupied space. Dana makes a very good point: inspector good will is golden. If in your case you can purchase it for $50 worth of baseboard, that is nothing compared to what it might save.

"On the few occasions I've read code for this issue, it says that each space has to be adequately conditioned. Sometimes it says that the heating or cooling facilities have to maintain a certain temperature in each room. It doesn't say that there has to be a DEDICATED piece of equipment or a SEPARATE outlet IN each space to do the conditioning."

That is correct ICF. However the manufacturers and builders are going to have to spend the money to educate the code council or this will continue to come up. For my part as an inspector I seldom see high performance envelopes, though some will pick 1 or 2 aspects (such as ICF or spray foam) but skimp elseware. I have yet to see the application in my AO where I'd be convinced that partitioned room's needs would be met by a minisplit on the other side of a closed door.

At the end of the day it is up to the builder or contractor to convince the code official. It is improper for the code official to take someone's word for it unless they own the result (i.e. engineer's stamp on the plans)......or for less than that someone can install a $50 baseboard.

So one can call the system ignorant or perhaps they might look at the example of CSST (corrugated stainless steel tube) gas pipe. In this case the manufacturers spent a lot of money educating inspectors and code writers as well as law makers. The result is their product is in the book and approved for use in many applications where it wouldn't have been a few years prior.

Parameters would have to be set defining the "tightness" required for the ductless to reach all (including partitioned) occupied space. Builder's would have to demonstrate that the criteria was met (either through check list or blower door test etc.). Only then will you find the application almost universally accepted.

Now who wants to pay for it?

Joe, thanks for an official's view. And thanks for illustrating why many of us feel so frustrated by officials. I have tried to make the point that my code official has stated that heat/cool can be "communicated" (your word) from the minisplit head location in the family room through a door into a bedroom. One door is OK. But that they would not pass the heat doing the same thing to the other side of the room to a second bedroom. If it works ok 1 direction, why not the other? We pay extra to meet CA title 24, have calc's done, show the BTU loss per hour, it's stamped by a state approved engineer, and STILL code official says no, I haven't seen it before. Your response is; OK, so spend some more unnecessary money. It may be the realistic, economic thing to do, but it's not right. If it is not protested in these kinds of forums, better choices will never become known.

Not all rooms are the same. If your unheated room is on a corner, with big windows, on the north or on a wind exposed side, has high ceilings, or double hung windows as opposed to awnings or casments, etc., etc., things can be very different.

McFish,
You selected one part of my reply to comment on ignoring the larger. Simultaneously suggesting I share the officials' knack for frustrating you.

This illustrates a professional blogger's frustration. I try to offer explanation and advice yet you choose to hone in on only a portion of my post and criticize me.

It also illustrates a layman builder's approach to the code, "I'll focus on this part (I got the heat calcs done"), but I wish to disregard this part.

While I'm not familiar with CA code (or which they use) are you? I can tell you (in codes) there is lot's of language about communication to adjacent spaces that includes: size of openings, size of communicating passages (such as a hallway), distance and maximum amount of communicated whatever. So the code may say that X CFM may be communicated to X adjacent spaces of X size not to exceed X CFM or BTU providing openings are within X feet and of X size and interim passage way is a minimum of X size.

Do it yourself builders seldom care to learn the whole code or why what the wish to do is not code worthy. They prefer to criticize the code officials and expect the inspector to educate them. Well, it is up to the builder to educate themselves on the code and demonstrate why what they do complies. In other words you would have to demonstrate compliance by doing the math and showing you have X amount of passage and openings to communicate X amount of CFM to adjacent spaces not to exceed X.

Are there inspectors that make up their own rules? Sure. Do I support that behavior? No. Do I think that when people complain on the internet they tell the whole story? Of course not.

That said-

The broader point you elected to disregard is that the company selling you the product that may work, has not done their work to get it approved for that application. Many inspectors will say "show me" before they say no.
In this case the minisplit equipment manufacturers have not shown code writers that your application is a good fit. Shoot the messenger if you like.......

In California Title 24 2008 is current code. Title-24 isit's much more comprehensive & explicit on all things energy than any version of the IRC. Under the code oversizing by more than 15% beyond Manual-J is expressly forbidden, which may be part of what is driving the inspector here (just WAG, no firm insights here). If you bump the size of the ductless to where it covers BOTH of the adjacent rooms it's likely that it's way more than 15% oversized for the actual space where the ductless head is located.

The fact that it's a modulating system with a large turn-down ratio, and that it operates at higher efficiency at part-load is not addressed in the oversizing dictum of the code, only one of many issues surrounding legally-commissioning a mini-split in CA. When codes gets too explicit it's easy for technology to get ahead of of the curve- CA has consistently dropped the ball on mini-split heat pumps for the last two versions of Title 24, but is making up at least some ground for in the (yet to be released) 2013 version.

Prior verbiage around how the refrigerant charge gets verified & inspected is only appropriate or even possible for traditional split systems, one of the more glaring issues being cleaned up for CA Title 24 2013. But I don't know if oversizing vs. efficiency factors issues received similar attention (I'm guessing not.) Either way, the new version doesn't go into effect until 1 January 2014.

Heat distribution for a better than code-R home in a zone-3 climate in CA are pretty tame compared to what might be a serious comfort issue at code-min in much colder climates. For most of those CA locations we're talking 99% outside design temps in the 30s (sometimes 40s) after all, which is pretty tepid stuff compared to Climate zones 5/6/7. Those are temps where my way-sub-code house stays comfortable in all quarters with just the wood stove in the living room. Unless the adjacent rooms have a whole lot o' glazing the heat loads of those rooms won't really warrant a stub of baseboard.

I don't have the books to compare Dana, but the IRC, by reference, includes a lot of other codes including the Energy Code, Manual D (for air distribution) etc. similar provisions exist about oversizing. The IRC is not intended to be a complete set of rules.
I have heard of local inspectors actually enforcing the oversize rule on gas furnaces which shows some of the ignorance to the code (as I can demonstrate that slightly oversized furnaces are actually less expensive to run than right sized).

Oversizing condensing gas hot-air furnaces is more of a comfort & noise issue than an efficiency problem.  At CA type heat loads it's often impossible to find furnace less than 2x oversized for smaller better-designed better-than-code houses.

I get that IRC is not intended to be anything like comprehensive, but Title 24 spells out different requirements for over a dozen CA climate zones- it's quite the beast!

Dana you miss understand.
The book itself is not intendend to be a "complete set of rules". But it does tell you where to look up the rules. Folks just ignore the 17 pages of referenced standards in the back. Literally hundreds of standards are cited that must be read elsewhere in scores of books from groups such as ASME, ASHRAE etc. though most have a fleeting notion that ACCA is part of the code (because of manuals J and D). The National Electrical Code (NEC) is virtually referenced in it's entirety and it is as big a book as the IRC.

Further the IRC is complimented by other ICC books such as the International Fuel Gas Code, International Plumbing Code, International Building Code, International Mechanical Code, International Electrical Code, International Energy Code etc.

Then don't forget "manufacturers' installation instructions". Furnaces, fireplaces, truss systems and many more things have their own rules which are by default, part of "the Code".

BTW the map of California above is similar to but not as inclusive as the IRC seismic and climate maps which include the entire country. If you look at ground snow loads for instance it shows more than a dozen for MI alone.

"The Code" is absolutely intended to be comprehensive just not a one volume set. If you put everything together and you have 50+ volumes and manuals.......that's a beast!

Thank you, Dana. To others; My original question was; county says it is ok to service 1 room through the closed door; why not the other room on the other side? No one offered a rationale, no one said what part of code i violated. If air is communicated sufficiently to one room, why not the other? PS; do you have a baseboard back up if your gas FAU goes down?

If you read between the lines, several posters answered that question.

Basically what the BI is saying is, I'll let you away with one room, not sure it will work but go for it. Now you want to use the same amount of heat to heat two rooms. Sure the circumstances are the same for both rooms but the demand is double. So no way. You can't prove that the heat will get to that corner.

Has anyone got software that says how effective a drywall wall is as a heat emitter? How do you calc. how much heat will flow when the doors are closed? How do you calc how much heat will flow when the door is open? Do we simply say- look, the total heat loss is X and I'm suppling that with this one head in this room and somehow it gets to the rest of the rooms?

As minis get more efficient, they are moving further north. What works in temperate climes, won't work for cooler ones. When the heat loss for a corner room with windows north of the 49th may be less then what it's portion of the total input of a heat plant is, the heat loss is still faster then the heat transfer from the heat plant to that room. The colder the design temp, the more likely there will be cold corners with unducted minis. This doesn't mean you can't use minis in colder temps if they are designed for that temp (and the cost of electricity is low enough) but you can't use them the same way as southerner do.

I am interested in why when we are in the radiant forum, all we get is -every thing starts with a room by room whole house calc but when we talk about minis, its just - oh throw it up there in the family room wall and it will look after everything.

Posted By FBBP on 21 Oct 2013 03:23 PM
If you read between the lines, several posters answered that question.

Basically what the BI is saying is, I'll let you away with one room, not sure it will work but go for it. Now you want to use the same amount of heat to heat two rooms. Sure the circumstances are the same for both rooms but the demand is double. So no way. You can't prove that the heat will get to that corner.

Has anyone got software that says how effective a drywall wall is as a heat emitter? How do you calc. how much heat will flow when the doors are closed? How do you calc how much heat will flow when the door is open? Do we simply say- look, the total heat loss is X and I'm suppling that with this one head in this room and somehow it gets to the rest of the rooms?

As minis get more efficient, they are moving further north. What works in temperate climes, won't work for cooler ones. When the heat loss for a corner room with windows north of the 49th may be less then what it's portion of the total input of a heat plant is, the heat loss is still faster then the heat transfer from the heat plant to that room. The colder the design temp, the more likely there will be cold corners with unducted minis. This doesn't mean you can't use minis in colder temps if they are designed for that temp (and the cost of electricity is low enough) but you can't use them the same way as southerner do.

I am interested in why when we are in the radiant forum, all we get is -every thing starts with a room by room whole house calc but when we talk about minis, its just - oh throw it up there in the family room wall and it will look after everything.

With four proximate air films a 16" o.c. 2x4 stud spacings a partition wall with half-inch gypsum both sides comes in at around U0.3-U0.6.  Gypsum alone is only ~U1, but the fraction with  framing wood runs about 0.24, and the air films gives the average a bit of a reduction.  Call it ~R2-R3-ish whole-wall if you prefer thinking in terms of R-value.

So the heat flow through the wall from conduction is:

U-factor x surface area x delta-T= heat transfer.

(In 'merican unit U-factors that would be square feet and degrees F)

Even with the doors closed there is at least some convective heat transfer as well, but that depends on how tight the door is to the threshold, etc.. With the door open the shape of the room, the location of the windows relative to the door, and the size of the door opening relative to the volume of the room all will affect the rate of convective heat transfer, but it's safe to say that in most homes the convective transfer of an open door is at least an order of magnitude higher than the conducted transfer through the common wall.

Of course it STILL always starts with a room-by-room heat loss calc even with mini-splits, and it would be stupid-on-a-stick to presume that doored off comfort will always work out with one head in the living room.  It's possible to calculate the approximate worst-case room-to-room delta-Ts using the basic principles, and it's something that SHOULD be done.  On a DER I was involved with a year or so ago in moderadly cool US climate zone 5 (zip code 01610) the 99% design temp was +5F and the delta-T on the doored off bedrooms were calculated as project specs evolved to make sure it was really going to be OK at the heating design temp with the doors closed. (FWIW it DID work out OK- the only discomfort issue is occasional AM overheating on a top floor bedroom that gets direct morning sun when the door was closed.  Heating comfort at night isn't an issue.)

In the radiant floor case the room by room loads are important to know since that determines just how much & what type of radiant floor would be required to handle the load, which has substantial effects on comfort, cost, and system efficiency.  But it's possible to heat the rooms next to a radiant zone with open doors, until it just can't keep up. (I've done this often at my not-so-high-R house.)

With ductless it's an issue of keeping the head sizes in the correct range for the loads, and the degree of potential discomfort-tolerance or auxiliary heating would be required. Yes they are modulating systems, but not infinitely modulating, and the smallest heads are in the ~7000BTU/hr heating range, which is a far bigger output than the design loads of a doored off bedroom in most higher-R homes. Installing a 7K+ head to handle a 1K load is not only expensive up front, it's an efficiency disaster, since it's way more than 2x, even more than 3x oversized even at min-modulation.