Comments on: Not All Mini-Split Heat Pumps Are Ductless!

By: Ryan

Ryan — Sun, 24 Aug 2014 01:10:31 +0000

I am looking to have a ducted
I am looking to have a ducted system installed in a 1926 Spanish style home with very limited attic space. If you or anyone you know would like to place a bit, please email me directly. Home is in San Diego, CA

By: Jason

Jason — Sat, 26 Apr 2014 23:53:28 +0000

The Fujitsu ARU series of
The Fujitsu ARU series of ducted air handlers are good to .36" ESP with about a 15% loss in rated capacity. .25" will net you the full rated capacity.
21 SEER for single head models with the ductwork in conditioned space.

By: David Butler

David Butler — Sat, 27 Apr 2013 19:39:53 +0000

@Tim: Without knowing more
@Tim: Without knowing more about your system and load, I can't be certain, but it's doubtful you could swap out your system with a residential ducted mini-split since the blower only has a fraction of the power of a conventional air handler (measured in available static pressure, 0.2"). Your duct system was most certainly not designed to operate at such a low static.

Mitsubishi, and I believe LG, produce more powerful ducted mini-split heads in their commercial lines, but the matching outdoor units are variable refrigerant flow (expensive) which you won't benefit from with a single-zone duct system. Minimum size is 3 tons.

The more important question is why? The only reason to consider ducted mini-splits is when you want to break up your home into zones with separate air handlers, or the total load is smaller than the smallest conventional system.

One more thing... there's a misconception about mini-split efficiency. While small single-zone ductless mini-splits (one compressor matched with one indoor unit, less than 1.5 tons) are available with very high efficiency ratings, the larger systems, especially those with ducted heads, only top out at about 15 SEER.

By: Tim

Tim — Sat, 27 Apr 2013 17:27:14 +0000

We had a 3 ton Carrier heat
We had a 3 ton Carrier heat pump installed in our home in 1983. Believe it or not, the compressor is still doing fine but we recently had to replace the air handling unit. I'm wondering if a mini split system is feasible for us when it's time to replace the outside compressor unit. Our air handler is in the attic and we would use the duct system that was installed for the original heat pump. What do you think?

By: David Butler

David Butler — Thu, 20 Dec 2012 12:13:53 +0000

@csaft, thanks for posting
@csaft, thanks for posting that. As I alluded to in my previous comment, ERV may be contributing to your problem. I have an issue with the common practice of using ERV's as the primary exhaust for high moisture areas such as baths, especially in homes with large moisture loads (e.g., teenagers) and/or small sensible loads.

Do you have an ERV exhausting from your baths? The problem is that the ERV will end up recycling a large portion of the bath moisture since a shower will generate exhaust air with a higher dew point than the outside air (except during rainstorms). ERV's either reject or recycle moisture depending on which side has the highest partial vapor pressure, as represented by dew point.

As you point out, it's definitely more efficient to use the HVAC system to remove moisture than any stand-alone system. In my experience, unitary air conditioners (without reheat) max out at roughly 50% latent capacity before getting into frost conditions. This can be accomplished with conventional HVAC equipment using a programmable ECM blower. However, with mini's, airflow and compressor capacity are inter-related and the controls are proprietary. Some models have a dehumidification mode, but it won't get anywhere close to 50% latent capacity.

By: csaft

csaft — Thu, 20 Dec 2012 09:25:34 +0000

I am a little late to this
I am a little late to this conversation but I thought I would give my experience having a passive house in the humid deep south. Our latent loads are 7-8 times our sensible loads. If you size your mini-split for the sensible (where it is most efficient) you are not likely to manage your latent loads efficiently or completely. If you size your minisplit for the latent load (where it is significantly less efficient) you will be well oversized for your sensible loads (which has its cycling problems). Depending on your location/latent load, supplemental dehumidification will potentially be unavoidable. And as pointed out, they are horribly inefficient for the scale of typical residential projects. While you can easily get mini-splits in the low to mid 20's SEER the most efficient stand alone dehumidifier tops out at about 5.5 SEER. Good luck.

By: Vic Hubbard

Vic Hubbard — Sun, 26 Aug 2012 19:38:19 +0000

A friend and builder recently
A friend and builder recently a completed an approximately 2000 sq ft house and used one interior DHP in the main area. He used a Panasonic bathroom vent fan unit in conjunction with ducting to circulate air for the bedrooms. Works like a champ. Extremely quiet and highly energy efficient.

By: Tim Hart

Tim Hart — Sun, 26 Aug 2012 18:31:56 +0000

I've sold hundreds of these
I've sold hundreds of these in both residential and Light Commercial, new construction and existing structure applications. 100% success, 100% satisfaction!

By: Allison Bailes

Allison Bailes — Wed, 22 Aug 2012 18:44:02 +0000

David B.:
David B.: Yes, this is one of the more powerful heads. We've had success using a little bit of flex and still getting good air flow with them.

David R.: Thanks. Actually, the drain does come out a little higher because there's an internal pump.

Bob: They also make sense where the homeowner doesn't want to see any ductless heads, but I agree in general with your statement.

Ryan: Looks like David Butler did a good job answering your question already.

Pat: I love that idea! Maybe that's what the Nest thermostat designers can work on next.

Ryan S.: Hear, hear!

Lance: Yes, I did mention in the article that was a different project, but as you point out, it was also a different HVAC contractor who did the install.

Thomas A.: Looks like a lot, but it works. The house you see above where the ducted head is installed in an attic has about the same amount of ductwork (or possibly more) as the one that's going in now and it has great air flow. Once we commission the new one, I'm sure it will be fine, too.

Jason M.: I agree with David Butler's response. You shouldn't need a separate dehumidifier with a tight envelope and an AC that's doing its job, not in Kansas anyway. And yes, 0.2" is static is low, yours allows for almost no ductwork at all. By the way, will you be in Denver at the Passive House conference next month? I'll be there.

Federor: Really? And you say that because...? Could it be that you prefer the smooth look of ductboard from the outside, as shown on your website, despite the problems that ductboard has? We never spec ductboard in our designs.

By: Jason Miller

Jason Miller — Wed, 22 Aug 2012 17:18:09 +0000

David, thanks for your
David, thanks for your response. I will send you a message through your website.