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How Off Were My Hvac Guys?

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Old 03-27-2011, 03:31 PM   #21
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Re: How Off Were My Hvac Guys?

Originally Posted by Dr Heat View Post

A house in Texas with a two ton load on a 4200 square foot home has something special going on. I doubt a typical heat gain heat loss annalist would come to Two tons simply using a manual "J". Someone took a risk based on previous experience.

Manual J is not the only heat loss heat gain tool we need to use.
The load calc was done with Manual J version 8.
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Old 04-08-2011, 06:48 PM   #22
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Re: How Off Were My Hvac Guys?

We are only guessing. That unit could have been sized correctly and the required insulation was not installed. Canned ceiling lights not insulated. Air infiltration etc. At one of our RSES educational meetings one of members performed a blower test. The local general contractor had a long talk with his crew and the HVAC contractor about all the defects that were found on this new house. Air gusts around window frames. Air being pulled from attic into the wall cavity returns etc.
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Old 04-09-2011, 07:50 AM   #23
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Re: How Off Were My Hvac Guys?

That is a point well taken, but no argument for rule-of-thumb load calculation. The designer is not responsible for as-built performance but can only go by the spec.

A SIP home in new construction and a foamed home in old are pretty sure bets, but nothing beats the combination of a good program and field experience.

Naturally a blower test reveals one of the critical elements of heat load analysis.
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Old 04-28-2011, 12:44 PM   #24
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Re: How Off Were My Hvac Guys?

Originally Posted by thom View Post
It's a shame. We did rule-of-thumb sizing for 50+ years and it worked, then, some smart guys with computers told us it wouldn't work and we believed them. Now we've got to buy fancy software and enter all the information into a computer to find out what size to put in. For some reason it doesn't heat or cool as well anymore. Must be climate change.
LOL.............and after going through all that, they don't make furnaces that are exactly the btu's that that fancy software calls what do you end up doing?.......putting in what you would have put in anyway.

On a side note..........if you have to put in a "over sized" furnace, put in a two stage so that the system will be "in the range".
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Old 04-28-2011, 06:12 PM   #25
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Re: How Off Were My Hvac Guys?

Originally Posted by thom View Post
I just assumed.....

Is everyone not required to submit plans for permit:
... showing duct location and sizing
... showing duct inslulation
... including a manual J calculation
... showing sizes of equipment and minimum efficiency

Maybe it's just Albuquerque that requires all that.
It's is coming to Oklahoma and about time. Plan on spending at least 1K for the program. I use Wrightsoft.


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