Thread: Exposed duct work at exterior

This is a packaged all in one system. Gas furnace and AC is combined in one
unit. The exposed duct work is insulated (inside ducts). I will be recommending that additional sealant be applied at joints and where duct enters home. I feel I should also be recommending insulation be installed at exterior. I don't see many installs with exterior ducts exposed like this.

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Flashing and sealant at the wall penetration is as important here as any penetration. The exterior duct, while it appears more exposed than acceptable, is not any different than in a well vented attic. The exposed duct has better insulation than the flex you find in attics and crawlspaces, so I would not recommend additional insulation. Not to say additional is not better, just not required to function as intended. The duct is galvanized so there are only a few coatings that will stick. Some that I have used is manufactured for mobile home roofs but I was not all that impressed.

I'm not sure that duct seal is approved for exterior exposure.

Also, there are no supporting straps on the duct and the duct needs to be properly supported and secured.

Additionally, when the sun shines on that duct and when it gets hot outside, the air inside is going to be affected.

I would recommend the duct be insulated, protected, supported and secured, and just plain installed in accordance with SMACNA guidelines and standards for exterior ducts. No, I do not know what those are, but I am sure they include additional things to what is shown in the photo and most, if not all and more, of what I said.

Originally Posted by Jerry Peck

I'm not sure that duct seal is approved for exterior exposure.

Also, there are no supporting straps on the duct and the duct needs to be properly supported and secured.

Additionally, when the sun shines on that duct and when it gets hot outside, the air inside is going to be affected.

I would recommend the duct be insulated, protected, supported and secured, and just plain installed in accordance with SMACNA guidelines and standards for exterior ducts. No, I do not know what those are, but I am sure they include additional things to what is shown in the photo and most, if not all and more, of what I said.

JP: I think it would be this one:

Sheet Metal and Air Conditioning Contractors' National Association

Residential Sheet Metal Guidelines


Published: 2001 Description:
FILE SIZE: 2.36 MB - The first edition of SMACNA’s Residential Sheet Metal Guidelines offers contractors, designers, builders and homeowners a source of expert information on the proper fabrication and installation of exterior sheet metal in residential buildings. Covering topics that include roof drainage systems, decks, chimneys, windows, doors and ledges, the new manual presents details and explanations based on and designed for low-rise residential buildings, up to three stories, that are used as single-family and multi-family dwellings. The guide also highlights details commonly used in residential sheet metal work throughout the industry. In addition to generic detail drawings, design data and the appendixes will help users to adapt the drawings to local climate and project conditions. Carefully examining the information along with the local climate conditions will enable users to select the proper details for practically any residential architectural sheet metal application.

Pricey little brochure at only $140!

Originally Posted by A.D. Miller

JP: I think it would be this one:

Sheet Metal and Air Conditioning Contractors' National Association

Pricey little brochure at only $140!

Nope, that covers the wrong subject.

It was this one, only slightly more pricey at $215 for the pdf.

HVAC Duct Construction Standards – Metal and Flexible


Published: 2005 Description:
FILE SIZE-4.2MB The third edition of the HVAC Duct Construction Standards – Metal and Flexible is intended primarily for commercial and institutional duct construction. This American National Standard (ANSI/SMACNA 006-2006) contains tables and details for constructing ductwork for ½" to 10" wg positive and negative pressures. This edition improves upon the second edition with expanded pressure class tables, separate tables for TDC/TDF construction and expanded tables for round duct construction including 6" wg positive and negative pressure and sizes up to 96". New in this edition is an engineering and design chapter to provide additional information to design professionals, double-wall construction details, new casing construction details and additional accessory items. The standard is applicable for construction using uncoated steel, galvanized and stainless steels and a limited range of aluminum ducts. This standard has been adopted in the ICC International Mechanical Code. Includes soft metrics. 390 pages. 3rd Edition, 2005.

The one you posted does not deal with duct work, the one above does.

Originally Posted by Jerry Peck

Nope, that covers the wrong subject.

It was this one, only slightly more pricey at $215 for the pdf.

HVAC Duct Construction Standards – Metal and Flexible


Published: 2005 Description:
FILE SIZE-4.2MB The third edition of the HVAC Duct Construction Standards – Metal and Flexible is intended primarily for commercial and institutional duct construction. This American National Standard (ANSI/SMACNA 006-2006) contains tables and details for constructing ductwork for ½" to 10" wg positive and negative pressures. This edition improves upon the second edition with expanded pressure class tables, separate tables for TDC/TDF construction and expanded tables for round duct construction including 6" wg positive and negative pressure and sizes up to 96". New in this edition is an engineering and design chapter to provide additional information to design professionals, double-wall construction details, new casing construction details and additional accessory items. The standard is applicable for construction using uncoated steel, galvanized and stainless steels and a limited range of aluminum ducts. This standard has been adopted in the ICC International Mechanical Code. Includes soft metrics. 390 pages. 3rd Edition, 2005.

The one you posted does not deal with duct work, the one above does.

JP: What a bargain!