Manual J on Change Out on Existing Sytems

[Mule]

I put this as a reply in another thread called sizing the HVAC system but I don't know how many actually looked at it so I will post here and hopefully get some answers.

We have started requiring HVAC contractors to submit calculations on older homes when changing out the condensor and inside unit.

The contractors are screaming! Well 3 or 4 of then anyway! They are saying that by requiring this that units will be undersized and will not cool efficiently. I think that you have to go by these guidlines and take all componants of the building in consideration.

Are any of you guys/gals requiring calculations on change outs?

Should I be requiring the HVAC guys to submit calculations? If I am reading the code correctly I think the code requires it.

Pros...Cons.... Help me out! I've contacted a lot of the cities in the area and none of them are requiring it. I'm starting to second guess myself! Wouldn't be the first time though!!

 

[georgia plans exam]

We don't require it here on change outs.

GPE

 

[Mule]

Hmm I didn't get very many responses.

I take it that some are embarrased that they don't require calculations to be submitted on change outs or that I am a total dufus for requiring the HVAC contractors to submit info on change outs!

What is it? Am I a dufus??????

 

[88twin]

yes we require manual J on change outs.

we are finding that most of the older units were greatly oversized, the old "rule of thumb"

yes some of the mechanical guys are screaming

had a mech contractor wanted to install 95K furnace, i asked for the calcs. to justify the size,

he provided the calcs (showed heat loss of 58K) and resubmitted for 120K furnace.

finally got it right, 90K H.E. modulated furnace 1st stage at 52K

 

[EPrice]

We haven't required it on change outs. I feel that manual J and manual D go hand-in-hand. If we can't tell how closely the duct system comes to meeting manual D, what problems may be introduced by requiring a smaller furnace in order to meet manual J? If the replacement furnace is comparable to what was there and what was there worked, it should continue to work satisfactorily. Replacing like for like may not make the situation better, but it won't make it worse either.

 

[JBI]

Mule - (Love the new avatar BTW) One reason they're screaming is because the smaller units mean smaller profits!

Another might be that they just don't know how to do the calcs and will need to pay someone to do them... again, less profit.

Seeing a trend yet?

 

[brudgers]

It doesn't take much creativity to get a Manual J to say whatever you want it to say.

And on an older home, it's even easier.

Unless you're going to review them closely, all you're doing is pushing paper.

 

[Uncle Bob]

Mule,

I wouldn't mess with it. How many jurisdictions even have manuel J and D; and I doubt that most that do; have no training how to use them.

If the majority of Mechanical Inspectors aren't trained for it; it should not be in the AHJ's authority to enforce it.

Uncle Bob

 

[Mule]

It doesn't take much creativity to get a Manual J to say whatever you want it to say.And on an older home, it's even easier.

Unless you're going to review them closely, all you're doing is pushing paper.

brudgers, Good common sense approach.

UB, We have received a couple of submissions on change outs. Looked at them and have no idea what I was looking at! Little alone what the heck to inspect.

It makes sense not to require submittal like brudgers stated....It doesn't take much creativity to get a Manual J to say whatever you want it to say.

 

[Uncle Bob]

My biggest complaint with new installations was putting the register just inside the door of the room; where the air would just go back out under the door. Of course the contractor saved a lot money with reduced duct length.

I've got to start leaving brick walls and windmills alone. I'm too old for this crap.

Uncle Bob

 

[Mule]

Due to the comments, our jurisdiction no longer requires submittal of Manual J for change outs.

Thank you very much.

 

[peach]

good choice, Mule