For the past 2 years we’ve been installing Mini Split Heat Pumps in our Green Renovation work on foreclosed homes.   And on all of them we’ve used ducts.  Some in attics, but most inside the building envelope.  We’ve been so happy with the performance and customer acceptane on all of them, that now it’s the only system we plan on using.

I’ve recently seen more and more references to “Ductless” Heat Pumps or “Ductless” Mini Splits … and a new Acronym, DHP has shown up.   (for us, that would stand for Ducted Heat Pump)

Nov 09 was the first I wrote about our "Hybrid" Ducted MiniSplit system on this renovation in Fresno, CA

Some may ask: Why is this important?    Well, words have power.  Words set the tone for what follows.    And words are attached to pictures in our minds.    So when you hear “ductless” your mind thinks of those indoor units on walls that we’ve been told are good for spot cooling and remodels with no access to hook up to the "real" HVAC system and little more.    That’s what our customers have in their minds also.   It’s also what the HVAC dealers have been told (from their respective manufacturers and it's what they pass on to the buying public)   It’s a big cycle and part of what holds it in place is the word ductless.

I believe that these small, inverter driven, Heat Pumps are the future as they are “right sized” for the better envelopes that we are starting to build and renovate.    The way we do them, they are ducted and zoned, right out of the box.   But public acceptance changes slowly.   Let’s not slow down that acceptance by continuing to call these fine little units what they dont have to be.

The system that we like is a “hybrid”    We use one outdoor unit, driving 2 zones inside.   One inside unit is a conventional Mini Split mounted high on a wall in the living room.   The other is mounted on the ceiling in the entrance to the hallway.  It has very small, metal ducts running down the hallway feeding each of the bedrooms and bathrooms.

Slide from Webinar showing Fujitsu Concealed unit with ducts going in to the top of the hallway.

This takes away the main objection that Americans have had against mini splits: that we must have forced air to every room.  We have found that these systems cost just about the same as a typical “American” style system,   13 SEER, 80%, single zone,with new R-8 ducts.   So it is considerably less money than a typical High SEER, zoned, 90 plus system.

Here are some slides I did for our Green Investor community last year   100316 How Mini Splits Help Sell Your Projects   Here’s from another webinar:  A Good Business?  How Long? Plus Ducted MiniSplit Update  Click the arrow on the right of the slide to move thru to the Mini Split installation photos.

Here’s the one thing I didn’t have at the time of those Webinars.   This project is in Fresno, lots of days over 100.   & PG&E has some of the most expensive kilowatts you can buy in America.   Check out those summer bills!

Bill Date Electric Usage (kWh) Electric Charges ($) Gas Usage (Therms) Gas Charges ($) Total Charges ($)
Feb 4, 2011 590 $72.34 23.0 $24.91 $97.25
Jan 5, 2011 583 $69.66 18.0 $19.14 $88.80
Dec 7, 2010 563 $66.99 23.0 $23.45 $90.44
Nov 4, 2010 328 $39.03 14.0 $15.79 $54.82
Oct 6, 2010 481 $57.24 12.0 $13.82 $71.06
Sep 5, 2010 480 $57.12 10.0 $11.67 $68.79
Aug 5, 2010 458 $54.50 9.0 $9.90 $64.40
Jul 7, 2010 375 $44.63 10.0 $10.65 $55.28
Jun 6, 2010 284 $33.79 14.0 $14.48 $48.27
May 6, 2010 297 $24.76 16.0 $14.08 $38.84
Apr 7, 2010 347 $28.93 21.0 $17.41 $46.34
Mar 7, 2010 388 $32.34 20.0 $17.41 $49.75
Feb 4, 2010 283 $23.59 18.0 $15.31 $38.90

Although our hybrid Mini Split Heat Pumps may not be the right solution for every situation, we have found them to be the best solution for everything we’ve come across in our Green Renovation Business.   I say they really deserve a serious look … Now that they are DUCTLESS NO MORE.

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Well, words have power.  Words set the tone for what follows.    And words are attached to pictures in our minds.

Nicely put.  I think this applies to the whole home performance field, where so often the pictures in peoples minds are completely distorted.  We need to be very careful in our attempts to simplify that we don't unwittingly create harmful inaccuracies. 


And nice article.  


Why don't you abandon gas?  At that low level of consumption, when you factor the meter charge alone, gas is very expensive.   (imaging paying a $1 service charge at the gas station.  Filling your suburban it wouldn't be noticed, but your model airplane?)  


Abandoning dangerous appliances makes this argument even more compelling. 

Speaking of words leaving incorrect images in people's minds...

There is nothing inherently dangerous about gas appliances. The number of residential fires initiated by gas or liquid fuels is about the same as the number initiated by electrical wires. Once user error is eliminated (most fires are caused by cooking and most fire deaths by smoking), electricity is a greater contributor to fire spread than gas.

In my 30-odd years as a volunteer fire fighter, I've responded to one major gas-caused fire and many dozens of fires ruled as electrical in origin.

Robert, nobody said anything about fires.  

If you've never measured the CO put off by a gas oven warming up, or heating cold water over a flame, maybe you would find that interesting.  

We are tightening existing homes like never before.  Homes with unvented appliances. Homes with Natural Draft appliances.  There is a tremendous amount of risk in tight homes and combustion appliances.  Much is known, and undoubtedly hindsight will uncover much that is currently unknown. 

You apparently build new, tight, highly insulated homes.  You install unvented or natural draft appliance in your new builds?  Why do I doubt it?  

I'm here to lean and share.  To fine tune my perspective and that of others.  People like Sean (below) appreciate my perspective as I appreciate his.   Why are you here if you feel you have nothing to learn?   If you have a complete inability to step outside yourself and look from another perspective before coming to conclusions, you may have little to offer. 

I get this sense of incredible resistance from most of your posts.   Are you so frightened that you'll discover something you've done in the past is wrong that you must rigidly define your perspective?  If you built to the best of your ability and knowledge at the time, what more could have been done?  Building science evolves, and we either evolve with the new information or we get stuck in a place that technology or new information makes obsolete. 


A lot of my long term contracting friend simply accept this is a fact.  They did the best they could then, and are doing the best they can now, and in 20 years some of what is best practice today will turn out to be wrong.  They do not have absurd expectations of perfection from themselves or others.  

Or are you afraid you'll learn something that forces you to alter current practices, and that frightens you?  There is an ethical pit there.  

From this and other posts I see an inability to comprehend retrofit issues as very different from new build issues.  This combined with your incredibly rigid and accusatory approach means those who could help you learn a thing or two will quickly become disinterested.  This attempt to share with you took a lot of effort.  I want more dialog, less argument.  If there is no reward in the information transfer, I'll stop investing.     

No, you didn't specify fire danger, but you didn't specifiy anything else, either - you simply made the blanket statement that gas appliances are dangerous.

So now, rather than take responsibility for the vagueness (and inaccuracy) of your comment, you launch into a major accusatory tirade replete with all kinds of (incorrect) assumptions about my psychology, which contributes nothing to these discussions and is a completely unnecessary and unprofessional diversion and distraction.

And, by the way, I always install gas cookstoves in my super-efficient and tight homes because no self-respecting cook would use anything else and that's always been what my clients want. The homeowners understand that the range hood is there to be used during cooking and there has never been an indoor air quality problem in my homes.

I've also done as many renovations and retrofits as new construction. And all my new homes contain a "natural draft appliance" called a woodstove.

Update on Ducted Systems.

This time in a different climate zone.   I've moved to Virginia = "Mixed Humid"  We were following grand babies.   And I just couldn't help myself ... when this foreclosure showed up in my little town, I just had to buy it.   Once you're infected with this Home Performance virus it's very hard to shake.    So what to do with this 92 year old balloon framed farm house with 8,000 cfm of leakage.    I was going to go totally ductless single point delivery Mini Splits, one upstairs and one down.  But plenty of research is happening on that.  So I decided to duplicate the Hot Dry project mentioned above in the Mixed Humid Zone.    

First we had to get that leakage down.   We went from 8,000 to 450.   Not Passiv, but pretty good for what we started with. Then the house sat for a while as decisions were being made.  The sitting and the final install of the HVAC and ventilation put the leakage back up to 700..... Still some work to do there.      The 2 ton unit was hung on the wall and half the freon runs thru the middle floor joists to a single indoor unit on the wall in the family room.  The other half goes to a small air handler mounted on the ceiling in a stair well.   A small duct system serves the three upstairs bedrooms.

We always use ventilation on purpose, this time the Panasonic ERV with 40 cfms continuous.

This project is being monitored by DOE and NREL.  It has just been commissioned so full data is not yet available.   The project manager however, said the HVAC kilowatt usage is "surprisingly low"   I will have more data  to present at the ACI regional conference in Pittsburg next month. Hope to see you there.   Here is a photo of the air handler and the start of the duct system ... mounted on the ceiling ... inside the building envelope.   I like the look of exposed ductwork.   After the testing, we'll see what the market thinks.   If necessary, I can cover it with a dropped ceiling.

"I like the look of exposed ductwork.   After the testing, we'll see what the market thinks."

Beautiful to an engineer, perhaps, but most people would consider that downright ugly.

8000 to 450, that's awesome!  How?  Do you have a blog or something we can follow?  

Great update Dave! So you traded humidity for grand-kids? I'm afraid that might happen to me someday too (both our girls are in colleges Back East).

Were your ears burning? Danny Parker and I were talking up your "hybrid" mini-split idea at his Zero Net Energy Class at PG&E last month. He said his 9 kBTU/h Fujitsu unit uses about the same amount of power as did just his old gas furnace blower motor. It's working so well that he's running his whole house -- plus a Chevy Volt -- on just a 5 kW PV system (in Florida no less)... and is still ZNE. Here's some very inspiring monitored data.

I have a friend in Santa Rosa CA who just put in a 3-headed multi-split and he's pleased (but this is way overkill for his small single-story, and not worth the efficiency penalty, IMO).

Any update on this work?  Seems manufacturers would provide an indoor coil that would accommodate placement in an air handler, trunk duct, or in place of customary A coil.  I've looked but not found so if I've missed, please direct.  VERY impressive DaveR!

Concealed units in hallway ceilings aren't new. Apartments have been using them for decades.


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