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Central vs. ductless?

Posted by mdmtnwmn (My Page) on
Thu, Jun 16, 11 at 13:03

Non-techie here, so please excuse these basic questions. I just seem to need a little more info than I have to get traction on research.

We're planning a 2500-2800 sq.ft 2 story home w/walk up attic in southern NH. It should be a 20-year home, maybe longer as a three-season home in the future. We'd like to make it as efficient as possible within our budget. It will most likely be SIPs construction, energy efficient windows, etc., in short, pretty tight. The immediate building lot is completely clear but sided on the west by a hill that does throw shade in the afternoon.

So, we are thinking about heat pumps that operate in low temps. Hallowell is discredited and out of business. From what I gather, Mitsubishi and Fujitsu make some. Some are ducted, some are not. And that is the point of my question today.

What are the essential differences between a system based on something like the Mitsubishi Zuba Central vs. Mitsubishi's Mr. Slim ductless systems? Is one more efficient than the other? Is there any advantage to having your home riddled with ductwork? I have read that the Mr. Slim is a "mini split"--what does that actually mean?

At this point, I am not savvy enough to understand a full discussion of SEER and COPs, etc., but hope to be as I go along. Any guidance in fairly plain English would be greatly appreciated!

Follow-Up Postings:

RE: Central vs. ductless?

An advantage of central in as tight a home as you are likely to build with SIPS, an advantage of ducts is that you can more easily build in controlled air exchange.

RE: Central vs. ductless?

about SEER: bigger is better. It is a measure of efficiency for AC (not heating so much).

Mini-split: Split systems have a physically separate compressor and evaporator/blower. I think it is called 'mini' because it can come in small sizes, like down to the window unit size. This means you can purchase a system for a single room or small space.

Tonnage: 1 ton of AC is 12,000 BTUs.

Usually, the smallest split system is around 2 tons, with the largest residential units being around 5 tons.

I've seen mini-splits as small as 8000 BTUs. A mini-split indoor unit is usually wall-mounted and does a single space. The bigger ones also can be ceiling mounted. For larger spaces, you get multiple wall units. The costs can add up.

I've seen that some of the HP versions are rated to fairly low temperatures for a HP. The other number to look at is 'HSPF' which is a measure of heating efficiency.

RE: Central vs. ductless?

With ductless, you need to add a humidifier separately. You tend to have more units - like 4 instead of 1. That drives cost up and you have to wonder if geothermal wouldn't be a better option...

RE: Central vs. ductless?

Check out the manufacturers' web sites for drawings of how minisplits are arranged. You get inherent zoning with them so that can save by not fully conditioning rooms that you are not using at the moment.

Indoor units can be rated as low as 6000 BTU for minisplits. One compressor (outdoor) unit can handle 1, 2, up to several, indoor units. Good minisplits run at part capacity very well. Minisplits will introduce no pressure differentials from room to room. That is not as much an issue with ducts within the building envelope as you are likely to do in a new building.

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