Manual J or Not? How to Tell If Your HVAC Design is Bogus (HVAC Load Training) 

Drunk on love

Hey thanks a lot Pam

EXACTLY, James! If you have proof that the problem is with the enclosure, not with your HVAC design or install, then you’re off the hook. Testing for the win!

The industry has just not been about careful, conscientious choices for anybody involved

When you ask 3 contractors to design your HVAC, their free "design" is worth what you paid for it. I would hope an architect would do better, but they are still competing for business to some degree, and they can cut hours on a design as well to make a higher profit. I don't know what software architects typically use, but it should be trivial for that software to design a HVAC system, since everything about a new build house needed for a HVAC design is already in the house design.

Great question! That question really stirs things up.

Alright, challenge accepted! Video forthcoming.

You don't have to guess buddy- I got you. Stay tuned.

@@HomePerformance I'd love to learn more! The hard part will be time constraints. I usually have about 2 hours in a customers home. I can't see the R value inside walls, the U factor of windows, and how well sealed the home is. Most homeowners don't even realize that these things are important. They just want a new furnace, or to add a heat pump, etc.

I hear you- but there are HVAC techs across the US, some of them my Mastermind students, who use their own blower door, infrared camera, inspection scope, etc. It’s not easy to go the extra mile, but once you do you’ll never have to compete the same way again.

Thanks Ric! Team effort!

Yes! It's so frustrating finding someone who's not just trying to replace a unit, especially when it comes to redesigning a system pre or post renovation. Is there a licensing or registration list for people that actually know what they're doing rather than HVAC professionals that are really just sales people?

Video forthcoming, guys, stay tuned

Try finding a person who actually wants to pay to improve their homes performance

Dustin, I’ve been doing this for a living for 15 years- there are LOADS of people who are willing to pay. People are willing to pay $6 for a better cup of coffee, pay more for a used car than a comprable new car, pay for the blue lights being hucked by HVAC distributors. They’ll pay for almost anything if they believe it’ll make life better- maybe we’re just generally bad at explaining why home performance is worth anything?

You can use actual historical data from ASHRAE, latest 2021

This is actually from a relatively progressive place, code-wise. You’d be amazed- I have another one coming that’ll floor you.

You get it, Niveous. For residential, Man J is the kind of load calc required per building code, and if you get ahold of Manual J and read just the first few pages, it’ll tell you this can’t be done on paper.

Video forthcoming on existing replacements KP

Rock on, Jeffrey, I’ll be here

Agreed, more govt regulation in this case would be a very helpful thing

@@HomePerformance or actual understanding and enforcement

Certainly

I appreciate that!

Sounds hot

Interestingly, these days it seems to be all over the place (but higher sensible than 75%) because of optimization toward better SEER numbers.

@@HomePerformance Yes, as evaporators get warmer the latent heat capacity decreases. You may find a system than meets your sensible capacity requirements, but falls short on latent.

You are so welcome

Ooh buddy, this was a big one. Probably 10 hours between 3D model and Man J software.

@@HomePerformance Seems like there's room for improvement in the software, if you had to do the modeling separately and manually transcribe from it. :+ )

Tweake, my whole home has one central return- it can be done right

@@HomePerformance no doors?

In my home? Yes, there are doors, but they’re undercut by 1”, which can return up to ~80 cfm. It’s in Manual D, actually.

@@HomePerformance would they do that here? It would not be the first time I've heard of installers telling the cust to "leave the doors open".

Practice practice practice ;)