"J" calcs

I’m curious, how many of you request the “J” calcs from the builder when inspecting a new build or at the 1 year warranty inspection.

In the Phoenix area 80% of these are done by the same contractor and I have been less than successful in obtaining them for my clients.

An HVAC contractor normally provides the labor and the equipment for the proper HVAC install. If the customer also wants the Manual J calculations from the HVAC contractor, he needs to pay for them. Naturally, the contractor has performed these calcs, but very seldom is he contractually obligated to provide them to the owners. If you’ve gotten a few contractors to provide you with copies of the Manual J calc, they were just being nice or didnt’ recognize the value of what they were giving away for free.

Down here they are required as part of the permiting process.

Marc, isn’t the contracor obligated to give the calcs to the owner? How can I tell my client they received the proper tonnage on the a/c unit if these calcs are not available? If they need to be purchased do you know what a normal fee would be?

Contractually, unless there is specific language, I don’t believe so. The contractor may be legally obligated to provide such information to the AHJ during the permitting process, and that information may be available to you through the AHJ’s office.

If you’re checking into whether the proper size equipment was provided and installed, who’s numbers would you want to use? The contractor’s (possibly flawed) calc? Or one you did yourself? In any event, doesn’t the installing contractor’s original proposal or estimate to the owner list tonnages, BTU’s of heating capacity, and/or model numbers of the original proposed equipment?

I don’t believe in “going rate”, but if there is such a thing for a manual J, it seems about a buck per conditioned 10 square foot is pretty typical. (ie, 250 bucks for 2500 conditioned square feet)

Way Way beyond the scope of any home inspection. I have taken and passed a few Manual J and D classes but would never comment on the design or functionality of a duct system in a report. If asked, I would tell them to hire an HVAC company.


I guess I still don’t understand. you are inspecting a new built and your client wants to know if the tonnage of refrigeration he received is what was designed for the house. You think that is beyond the scope of your inspection? I don’t think you should do the calculation, I just feel you should have access to it.


I agree with Kevin above, don’t cross that bridge of opinion, unless you’re willing to put it in writing and possibly end up in somebody’s court.
I always defer to the HVAC Installing Contractor, who by the way will be warranting his installations, not only from a mechanical operation standpoint but from a operational comfort level as well.
Most states have/mandate design requirements, typically originating through ASHRAE standards and then “tweeked” to meet states energy standards. Then the HVAC Contractor designs his systems based on his “J Manual” calculations, which you have to “*** u me” are correctly run. Then you have to assume again, that the system is matched and installed properly, not just from a life-safety standpoint (Code), but from a mechanical/balance (comfort)standpoint.
There are just to many facets to a proper or improper design.
I have, or had 20+yrs. of Design Engineering experience in the HVAC industry (Residential,Commercial & Industrial) and the changes in the Industry are almost daily.
I think your best advice to your Client is - See & Talk to the Expert who installed the system, and if it not a new system and there are other questions about the system besides the sizing, again, call the expert.


Like Greg says,way too many variables to get involved with manual j calculations as a home inspector.Defer to installing contractor.Matt Berman

In my previous life I lived with the Manual “J”…and “D”…and others…

In this life—I never heard of them.