genduct

mgbinspect good for you in doing your homework. They were right, ductboard IS the superior product! Its leakage is 1/8 of sealed sheet metal. Most of the problems reported are a function of people who don't know, or care Or Care to know the proper way to fab or SEAL the duct with UL 181 tape ( not duct tape) Personally we have fabricated millions of Sq Ft of ductboard for commercial work. When you go past the Ft McHenry tunnel on 95 in Baltimore, look off to the right (going south) and see the 8 story 1926, 9 story building that was Montgomery Wards Catalog Bldg (1.2 million SF) The anchor tenant of 500,00 sf of space is the MD Dept of the environment We fabed 250.000 sf of ductboard. The top floor is M&T Bank computer/ check clearing. wwe got fiber glass duct hanging off of 2 110 Ton rooftops with sizes like 52x30. So when I hear that someone can't make an 18x18 plenum stay together on a 2 ton split I find it pretty annoying. By the way mold doesn't grow on galvanize or board, it grows on dirt regardless of what the duct is made of. Dirt thinks the rough surface of galvanize looks the same as board. It takes liquid water and dirt to grow bugs! Oh and by the way the IARC people who raised the health issue 20 years ago have reversed themselves and in 2002 said it was OK Check the NAIMA,ORG site. If you would like to hear what 30 years of fabbing this mat'l has taught me Feel free to email me. You're on the right track but there are places it doesn't belong for practical reasons not technical. Too much info for this post.

A joist or stud space (with wooden studs) can be used as return duct and you think this standard building material is worse? If that is true it certainly sounds like an inconsistency.

My understanding that only pipe NOT allowed is GAS pipe. water or even DWV should be OK. For the record, the new ACCA MAN D discourages the use of building cavities for returns. Couldn't outlaw it because it is still ok in IRC

Depends on system type, VAV vs constant Volume and the real deal is the controls. Only useful as part of a larger retro. Pretty technical You just may want to suggest looking at the possibility with someone who knows this cold or you may wind up looking foolish.

PS high supply temp is either warm air getting sucked in or lack of insulation

The old, but still useful rule for return duct sizing from ACCA MAn d is 700 FPM velocity in duct so about 1200 CFM/ 700 FPM =1.7 SqFt or 250 SqIn or a 24x10 duct with a grill 2x that or 24x24 The limited the velocity because of potential noise problems

What would explain a contractor NOT wanting to replace a unit like that? Was he at the wrong address? What was age of equipment? Should have replaced both in and out if airhandler was that bad.

New here and glanced at some of replies but, the gauge pressure is set high enough to get the water to the top of the system plus a little more 2.31 ft/ psig. Not only warm air ( the other fluid) but hot water also rises and cold drops so the gravity systems have been working without pumps for years. The inefficiency is offset by the mass of the 'iron that is hanging off them and the boiler doesn't cycle as much as you might think. In the early days they had trouble making pumps and gaskets that could handle the heat so pumps weren't just expensive but also a maintenance problem. Also the reason why they were on the return side And finally if you do have to be careful with return temps too low since the products of combustion are CO2 and water. Don't want to try to make a standarrd boiler become a condensing boiler since it then will rust to nothing. Any help?