Thread: HVAC Help Please

I have been inspecting numerous new homes that have the air handlers located in the attic space. The AHU are suspended from the roof trusses with metal straps at each corner. The straps are installed behind the AHU casing. I cant see how far down the straps are connected because they go into the casing/shell.

The code says strapping shall be at points within the upper and lower one-third of the AHU vertical dimensions.

I am not sure if I understand the code properly where it says the upper and lower one-third.

Any explanations would be appreciated, thanks in advance

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You are looking at it hanging horizontally. Divide the case into thirds with imaginary vertical lines. The straps will be in the left and right thirds. Hopefully, the unit is level.

Thom,

Thanks for your reply.

I'm doing these inspection as QA inspections for a builder. He said the AHU only have the upper third supported and not the lower third.

The AHU are suspended with metal factory straps at all four corners connected to the units.

I'm not sure what he means when he says they do not have lower third support.

You are welcome. However, wait for more replies. I thnk I know what you're asking. Wait for some other guys who might have a different take on what you mean.

I have no idea what your builder means when talking about support only on the upper third. Can't picture that.

Calling Dr. David R....Calling Dr, David R

Thom,

I will wait for Mr Jerry Peck to come to the rescue

Thanks again Thom.

Originally Posted by Matt Hawley

The code says strapping shall be at points within the upper and lower one-third of the AHU vertical dimensions.

I am not sure if I understand the code properly where it says the upper and lower one-third.

???????

Where does it say that? New one on me.

But ... if it is there, to me, that would mean you have an air handler hanging horizontally (or vertically), you draw to imaginary lines through it, one line 1/3 up from the bottom and one line 1/3 down from the top, then attach the support straps in the lower third and the upper third.

That would make sense in that if you attach the supports at the bottom only, the thing could flip over, and, if you attach the supports at the top only, the cabinet could come apart.

Attaching at the bottom carries the weight of the unit, attaching at the top keeps if from flipping over.

Does it say that in the manufacturer's installation instructions? I would think it would be there more than in the code itself.

Unless ... it is referring to *where* you attach them at the trusses, you would *not* want them attached in the center third, that would lead to deflection of the trusses more likely than if attached to the truss near the top of near the bottom.

Just guessing here and shooting from the hip.

Jerry,

Here is the reference FBC M1307.2

I think you are correct. The only thing is the metal straps run along the interior side of the cabinet. I'm not able to see if the straps are attached at the bottom third of the AHU.

What you said makes perfect sense. You should get a 1-900 phone number and charge me by the minute for you technical assistance, seriously thank you for always helping us out.

Thanks Jerry and Thom for your help.

I think what this boils down to is M1307.1 General: Installation of appliances should conform tothe conditions of their listing and label and the manufacturer's installation instructions. The manufacturer's operating and installation instructions shall remain attached to the appliance. (bold mine)

Since these are new construction, you stand a chance of having them handy. Snatch a set, take them down stairs and read them. You'll know if what you're looking at is right or wrong.

Matt, could you have gotten the code idea from M1307,2 where water heaters in seismic zones are discussed?

Melborne, great town.

Thom

Thom,

The builder actually brought the code to my attention. The only thing is I am not able to get a visual on the bottom third of the metal straps to actually confirm if they were attached to the unit.

To be honest I was not sure if that was in fact what the code was saying. What Jerry said does make perfect sense. I did see an installation manual and will grab one. I have 22 to inspect this weekend and 43 in all. The builders big concern is that the systems lack bottom support and only have top support. I want to make sure i'm on the correct path with the inspections.

Thanks to you and Jerry I'm pretty sure I know what the builder is talking about. I will do further research and grab an installation manual.

Thanks again for your help. Melbourne is a great town. I spent a weekend in Corpus Christi in my Air Force days, also a nice area. Thanks again Thom and I hope business is well.

Matt,

I must have been a bit loopy last night as I did not comment on what I thought was the more important issue, and I kept telling myself to make sure and remember to do so.

"The straps are installed behind the AHU casing. I cant see how far down the straps are connected because they go into the casing/shell."

The AHU panels are designed to fit just so and be as air tight as possible. Inserting a strap between the panel and the unit frame only makes for air leaks.

One thing I've seldom found was the required notice, required by 13-610.1.ABC.3.5.2.4

Originally Posted by Thom Walker

You are welcome. However, wait for more replies. I thnk I know what you're asking. Wait for some other guys who might have a different take on what you mean.

I have no idea what your builder means when talking about support only on the upper third. Can't picture that.

Calling Dr. David R....Calling Dr, David R

Thanks for paging me Thom sorry I took so long to get back here.

Have to admit I have never seen them hung with metal strapping in my area & I am really glad.
I don't see how the air handler could have any type of support hanging there like that with straps.
We have always used 3/8" threaded rod & unistrut with this being bolted to the cabinet.

The air handlers made by Trane & American Standard already have female connections on the ends of their air handlers for threaded rod to tie into.

I see no practical application for placing them inside the doors except making the doors a pain to remove & reinstall.

(2) Cat IV Lennoxs installed '98. Same house, same basement. Cause for concern?

Originally Posted by Matt Hawley

Thom,

Thanks for your reply.
I'm doing these inspection as QA inspections for a builder. He said the AHU only have the upper third supported and not the lower third.

The AHU are suspended with metal factory straps at all four corners connected to the units.

I'm not sure what he means when he says they do not have lower third support.

Matt,

Either your builder is testing your understanding of the code or he's inadvertently asking you to test his own understanding because he really just does not know himself. (I suspect the latter.)

What "you said"/"he said" make no sense to me personally in regard to HVAC equipment without further explanation and possibly some pictures.

I say this as a long time licensed HVAC contractor in the state of Texas and an ICC code certified mechanical contractor.

I don't personally live in Florida myself but I gather from Jerry Peck (who does) that Florida currently follows a locally appropriate hybrid of the International Residential Code (IRC).

Your builder is most likely working entirely out of context (just as Thom Walker pointed out earlier). M1307.2 within the IRC (and I suspect within the adopted FBC variation) has more to say about earthquakes and horizontal/lateral movement/displacement of top heavy installed appliances in seismic design categories E, D1, and D2 than it does specifically about horizontally installed HVAC equipment in Florida which resides in the same code based seismic zone as Texas where the posed threat of lateral/horizontal displacement where pipe breakage poses little or no specific threat.

Ask the Florida builder to take a look at the seismic maps associated with the FBC/IRC code from chapter 3 and see if Florida resides in seismic design categories E, D1, or D2 as opposed to C, B, A.

Matt,

Our primary concern here along the Gulf Coast [From FLA to TX] is from windstorm damage and not from earthquakes. Tell that builder to wake up and smell the coffee as it relates to his particular geographical area!

He would not be a West Coast "transplant" would he?

So, I can assume the corrosion at that Lennox is not a concern?

Originally Posted by Michael Thomas

So, I can assume the corrosion at that Lennox is not a concern?

I don't see a drain hose connected to that inducer housing Michael, I would say that is definite cause for concern.

Update on this:

Per Lennox tech support (972-497-5799, BTW, and not an easy number to get) for this model furnace, a G26Q3/4-100-3:

1) That degree of corrosion is indeed indicative of a problem that should be addressed.

2) The furnace is shipped with the inducer drain plugged with a knockout, and opening and plumbing it is a optional field modification.

3) FWIW, Lennox did not believe that draining the inducer would solve the problem, which they felt was likely related to excessive condensation in the exhaust piping, a problem that needed to be fixed at its source.

Michael,

I presume this is an upflow system with an evaporator coil on top of the furnace? I would look into the possibility that the rusty spot in your picture is the result of dripping from the refrigerant lines or the coils drain system.

The rusty spot may not be the result of furnace operation in heat mode but rather a consequence of the system operation in cooling mode. Just a thought.

No central AC at this property.