FHB Logo Facebook LinkedIn Email Pinterest Twitter X Instagram Tiktok YouTube Plus Icon Close Icon Navigation Search Icon Navigation Search Icon Arrow Down Icon Video Guide Icon Article Guide Icon Modal Close Icon Guide Search Icon Skip to content
Subscribe
Log In
  • How-To
  • Design
  • Tools & Materials
  • Restoration
  • Videos
  • Blogs
  • Forum
  • Magazine
  • Members
  • FHB House
  • Podcast
Log In

Discussion Forum

Discussion Forum

Second opinion(s) on Mini-duct AC system

darrel | Posted in Energy, Heating & Insulation on April 25, 2002 06:13am

Well, I’m FINALLY getting around to preparing for installation of a Unico mini-duct AC system for my house. I had the company come out to do a walk-through and get data for the estimate.

I have not reason to doubt anything the rep said, but I’ve read a bit about HVAC guys not always being up-to-speed on the mini-systems, so I thought I’d post the info I have so far and see if anyone wanted to add anything.

Quick background:

The house was build in 1929 and has hot-water floor-board radiator heat. It’s a 1 1/2 story (upper floor is one room). The basement is unfinished at the moment.

The first floor is about 850 square feet, the second about 470, and the basement, eventually will have about 550 finished square feet of space.

He recommended a 2 ton unit, a main 14″ return system (on the first floor) and the appropriate number of exhausts for each room (most with one, 2 in the living room, 3 on the third floor). This all sounds good to me. The only immediate concerns I had are the following:

1) He claims the 3 vents on the second floor are enough to cool that room, provided we keep the door closed to the upstairs. My concern is that there is no return in that room. Will those three vents be enough to pump cool air into the room without a return? (I’m no expert, but it would seem to me that those three vents would have to work quite hard to pump air into an already ‘full’ room. Since the path of least resistance would be for the air to go into the main floor, as it has a return vent, little cool air would make it to the second floor).

2) He suggested that we don’t vent the basement at all, as it is relatively cool, and instewad just use 2 mini-returns to pull out the humid air. He DID say that we would still want to run a dehumidifier in the summer. Is that an ideal situation? Would it be better to run a few vents in the basment and let the AC to most of the dehumidifcation?

Reply
  • X
  • facebook
  • linkedin
  • pinterest
  • email
  • add to favorites Log in or Sign up to save your favorite articles

Replies

  1. darrel | Apr 27, 2002 06:19pm | #1

    2 Quick follow-up questions

    1) has anyone had experience with installing both Space-Pak and Unico systems? This particular contractor has experience with both and felt they were pretty evenly matched in terms of performance and ease of installation.

    2) Has anyone installed these in the floor? That would be the easiest installation for us. Any reason to add a few feet to the duct length to get the vent up on the wall or celing?

    1. User avater
      Mongo | Apr 28, 2002 10:06am | #3

      Yes, you can vent through the floor, but furniture/traffic patterns can be tough to work around.

      Often it's tough to come out of a wall because of the tight turn radius, which wil lead to a noisy outlet. There are toe kick boxes that have been used in walls, but they are pricey. You can come out of a soffit as well, a little more room there to make the turn. The only negative for ceilings is heating from high ceilings, but that's not a concern of yours.

      One other "rule-of-thumb" that you can consider...usually, you can run about 5-6 outlets per ton of cooling. You have 2 tons, so you should have 10-12 outlets.

      Ballpark. Fewer outlets could mean short-cycling of your system which may give insufficient dehumidification. Fewer outlets could also mean too much air being pushed through too few outlets. that means noise.

      1. darrel | Apr 29, 2002 09:32pm | #4

        Mongo:

        Thanks for all of the feedback. I appreciate it.

        A few notes:

        re: the unico plenum...I will not be using that, per yours (and others) past comments regarding the fiberglass. I was originally hoping to use spiral ductwork, but the return plenum would have to be 14" in diameter, so we'll probably go with rectangular ducting...as much as I dislike that look comparet to the cylindrical ductwork.

        I should clarify the main return duct will be on the main floor, split in half so that it takes from both the hallway and the main living room. The upstairs (second floor) will have no return...one concern of mine, and the basement WILL have two mini-returns branching off of the main return. (and, now that I think about it, I may go ahead and look into running one mini-return up to the second floor to even it out a bit).

        At this point, I think we have a total of 10 vents, so we have room for a handful in the basement.

        I'm not too concerned about noise. I can live with noise. I can't live with extreme heat+humidity. That said, there's nothing wrong with an extra vent as it'll be easy to do the first time.

        My main concern is that I get the maximum dehumidification out of the unit...which, I believe has to do mostly with a properly sized condensor and proper air-flow rate. I really don't want to be running another dehumidifier in the basement, so I'll be checking with this place to make sure we have the vents figured out properly for the basement.

  2. User avater
    Mongo | Apr 28, 2002 09:58am | #2

    A couple of ideas...

    First, with the high-velocity systems, it's not a good idea to stretch the limits of cooling. Why? Because of noise.

    Your designer should have donw a pretty detailed calc to get the cooling loads for each room. the amount of required cooling for a room translates into so many outlets for that room. With these systems, a "full outlet" is an unrestricted outlet with a certain length, say 15' long mini-duct, feeding that outlet. For each foot that the outlet gets lengthened, the efficiency of that outlet goes down. If the outlet is shorter, it can get noisier from turbulent airflow at the outlet.

    If, for example, a room needs two "full ducts," that means that two 15' ducts will cool the room. The problem is that may be a littel noisy. While i cost more in materials, it may be better to intall three duct, each counting as two-thirds of a full outlet. You can drop the oulet from a "full" to a less efficient "two-thirds of an outlet" eaither by lengthening the run of mini-duct or by installing a baffle plate where the mini-duct departs the plenum.

    What this all gets down to is that if the installer claims three outlets "should" be able to cool the room "as long as the doors remain closed"...you may want to consider running a fourth outlet to that room, and choke any or all down until you get the proper amount of airflow to cool the room. Those three, if running hard, may just be too noisy...or they may not cool the room adequately. The beauty of these systems is that there should be no operator restrictions (closed doors, etc) to get adequate cooling in your home.

    Hi-v systems are mainly used for remodels or for with homes with RFH. Often times a whole floor can be cooled with only one main air return for that floor. This differs from conventional AC.  However, if an area can have a return run without much problem, why not? If an area has a return, why not a supply as well? If your basement is currently unfinished, and you run a return with no supply, a question...do you have a furnace or other combustion sources in your basement that could possibly be back-drafted? It may not happen, but it's something to consider.

    I like to see a return on each floor. I like to see each floor get it's own supply plenum. Even if you only have a few outlets on the second floor, sometimes it's best to run a takeoff from the main plenum up to the second floor, then run your mini-ducts off that takeoff. Shorter duct runs, and as long as access isn't a problem ot run that takeoff, it will usually ba a wash or even a savings in material.

    Hi-v is great at dehumidifying. Unless there are strange things going on in your basement, the hi-v should be able to dehumidify your finished rooms down there. Still, your designer knows you house better than I do.

    Space-Pak vs Unico? Overall, they're both pretty good. Unico has better marketing so they're better known. They both have good hardware, though I'd give the edge to Unico. They both have good ducting, though I'd give the edge to Space-Pak. Easy snap-together assembly.

    I highly encourage you to not use the pressboard FG duct for your main plenum. It's be shedding shards into yout house for who knows how long. Use spiral of regular metal duct ad insulate it well.

    Another point...SEAL ALL OF THE DUCTING. All seams. All unions. With Al foil tape. THEN insulate the ductwork, and SEAL the foil on the insulation with Al foil tape.

    Off to bed...

    Edit: Just wanted to add a final note. If your desinger/installer has a good reputation and can expain his design to you and have it make sense...it's likely to be a good layout. He knows you house better than any of us do. Every house, especially remodels, has a few quirks. Then again, some installers do too.<g> If you're truly concerned, call Space-Pak/Unico ans talk to a tech rep, just to see if this guy's ideas (3 outlets with door always closed, and basement return but no supply, etc) mesh with Big Brother's ideas.



    Edited 4/28/2002 3:12:49 AM ET by Mongo

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

Video Shorts

Categories

  • Business
  • Code Questions
  • Construction Techniques
  • Energy, Heating & Insulation
  • General Discussion
  • Help/Work Wanted
  • Photo Gallery
  • Reader Classified
  • Tools for Home Building

Discussion Forum

Recent Posts and Replies

  • |
  • |
  • |
  • |
  • |
  • |
View More Create Post

Up Next

Video Shorts

Featured Story

Podcast Episode 684: Masonry Heaters, Whole-House Ventilation, and Porch Flooring

Listeners write in about fireplaces and ask questions about whole-house ventilation, traditional porch flooring, and gutter sealants.

Featured Video

Micro-Adjust Deck-Baluster Spacing for an Eye-Deceiving Layout

No math, no measuring—just a simple jig made from an elastic band is all you need to lay out a good-looking deck railing.

Related Stories

  • Podcast Episode 684: Masonry Heaters, Whole-House Ventilation, and Porch Flooring
  • FHB Podcast Segment: Repairing an Old Home While Maintaining Its Integrity
  • Tools and Gear for the Moms Who Get it Done
  • An Easier Method for Mitered Head Casings

Highlights

Fine Homebuilding All Access
Fine Homebuilding Podcast
Tool Tech
Plus, get an extra 20% off with code GIFT20

"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Fine Homebuilding Magazine

  • Issue 331 - June 2025
    • A More Resilient Roof
    • Tool Test: You Need a Drywall Sander
    • Ducted vs. Ductless Heat Pumps
  • Issue 330 - April/May 2025
    • Deck Details for Durability
    • FAQs on HPWHs
    • 10 Tips for a Long-Lasting Paint Job
  • Issue 329 - Feb/Mar 2025
    • Smart Foundation for a Small Addition
    • A Kominka Comes West
    • Making Small Kitchens Work
  • Issue 328 - Dec/Jan 2024
    • How a Pro Replaces Columns
    • Passive House 3.0
    • Tool Test: Compact Line Lasers
  • Issue 327 - November 2024
    • Repairing Damaged Walls and Ceilings
    • Plumbing Protection
    • Talking Shop

Fine Home Building

Newsletter Sign-up

  • Fine Homebuilding

    Home building tips, offers, and expert advice in your inbox.

  • Green Building Advisor

    Building science and energy efficiency advice, plus special offers, in your inbox.

  • Old House Journal

    Repair, renovation, and restoration tips, plus special offers, in your inbox.

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters

Follow

  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X
  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X

Membership & Magazine

  • Online Archive
  • Start Free Trial
  • Magazine Subscription
  • Magazine Renewal
  • Gift a Subscription
  • Customer Support
  • Privacy Preferences
  • About
  • Contact
  • Advertise
  • Careers
  • Terms of Use
  • Site Map
  • Do not sell or share my information
  • Privacy Policy
  • Accessibility
  • California Privacy Rights

© 2025 Active Interest Media. All rights reserved.

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

  • Home Group
  • Antique Trader
  • Arts & Crafts Homes
  • Bank Note Reporter
  • Cabin Life
  • Cuisine at Home
  • Fine Gardening
  • Fine Woodworking
  • Green Building Advisor
  • Garden Gate
  • Horticulture
  • Keep Craft Alive
  • Log Home Living
  • Military Trader/Vehicles
  • Numismatic News
  • Numismaster
  • Old Cars Weekly
  • Old House Journal
  • Period Homes
  • Popular Woodworking
  • Script
  • ShopNotes
  • Sports Collectors Digest
  • Threads
  • Timber Home Living
  • Traditional Building
  • Woodsmith
  • World Coin News
  • Writer's Digest
Active Interest Media logo
X
X
This is a dialog window which overlays the main content of the page. The modal window is a 'site map' of the most critical areas of the site. Pressing the Escape (ESC) button will close the modal and bring you back to where you were on the page.

Main Menu

  • How-To
  • Design
  • Tools & Materials
  • Video
  • Blogs
  • Forum
  • Project Guides
  • Reader Projects
  • Magazine
  • Members
  • FHB House

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Popular Topics

  • Kitchens
  • Business
  • Bedrooms
  • Roofs
  • Architecture and Design
  • Green Building
  • Decks
  • Framing
  • Safety
  • Remodeling
  • Bathrooms
  • Windows
  • Tilework
  • Ceilings
  • HVAC

Magazine

  • Current Issue
  • Past Issues
  • Magazine Index
  • Subscribe
  • Online Archive
  • Author Guidelines

All Access

  • Member Home
  • Start Free Trial
  • Gift Membership

Online Learning

  • Courses
  • Project Guides
  • Reader Projects
  • Podcast

More

  • FHB Ambassadors
  • FHB House
  • Customer Support

Account

  • Log In
  • Join

Newsletter

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Follow

  • X
  • YouTube
  • instagram
  • facebook
  • pinterest
  • Tiktok

Join All Access

Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features.

Start Your Free Trial

Subscribe

FHB Magazine

Start your subscription today and save up to 81%

Subscribe

Enjoy unlimited access to Fine Homebuilding. Join Now

Already a member? Log in

We hope you’ve enjoyed your free articles. To keep reading, become a member today.

Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine.

Start your FREE trial

Already a member? Log in

Privacy Policy Update

We use cookies, pixels, script and other tracking technologies to analyze and improve our service, to improve and personalize content, and for advertising to you. We also share information about your use of our site with third-party social media, advertising and analytics partners. You can view our Privacy Policy here and our Terms of Use here.

Cookies

Analytics

These cookies help us track site metrics to improve our sites and provide a better user experience.

Advertising/Social Media

These cookies are used to serve advertisements aligned with your interests.

Essential

These cookies are required to provide basic functions like page navigation and access to secure areas of the website.

Delete My Data

Delete all cookies and associated data