Manual J or Not? How to Tell If Your HVAC Design is Bogus (HVAC Load Training)
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- čas přidán 8. 01. 2023
- If you ask for the HVAC design calculations for your project, you might get handed literally anything from scratches on a napkin to a 50 page jargon-filled binder. Here’s an example of a calculation that might look legit, but is actually very misleading.
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Always superb! It's unusual to find someone understanding Manual J, D and S as well as this.
Hey thanks a lot Pam
Your Sketchup model for totalling SF is fantastic 😍. Keep fighting the good fight. Architect & Framer in NJ here🙋🏻♂️, my hat is off to you sir.
Thanks Ric! Team effort!
When we build our home we got 3 done from different contractors for the same house and none matched. All were provided the exact same plan. They all said 1000 sq ft a ton or less. We finally gave it to an energy engineer and their numbers actually made sense. It came out to 1700 sq ft a ton.
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.
Thanks for sharing!!! I really appreciate what you do.
I appreciate that!
I can do a manual J, manual D, mastic the duct to death, insulate the metal duct with R8 insulation to the best of my ability, and then I see that the insulation contractor appears to hire 6 year olds to install the insulation in the home. I live in Kentucky and we have an HVAC inspector, but not a building inspector. The HVAC inspector actually tells me he hates the Energy Code, and that I worry too much. Thank you for what you do!
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!
How do you handle different climate conditions in different rooms? Things like indoor pools, wine cellars, computer server rooms, etc.
Great question! That question really stirs things up.
Alright, challenge accepted! Video forthcoming.
Lots and lots and lots of homes in existence fall in this bogus HVAC design category. I swear the 80's and 90's builders were drunk when installing HVAC ducting.
Drunk on love
This is wonderful, Thank you for sharing this information.
You are so welcome
A 100F Design Temperature vs 91F would increase the cooing BTUs but also make that cooling power available at the 1% or .5% design day.
So I found you from Matt Risinger's channel fyi. One thing I've heard no one talk about is non standard spaces and non standard heat sources. Does manual J allow for the inclusion of things like welding, shop doors opening and closing, air compressors, servers, ovens etc into the calculation. If it does not, do you have recommendations on literature to read about this. I don't have my manual J book yet, but nerd out on doing things the correct way.
I live in Atlanta. I’m going to be building a new home in Florida later this year or early 2024. I’m going to hire you for anything HVAC related.
Rock on, Jeffrey, I’ll be here
@12:05. The software provides SHR for 0.75 because equipment is often rated at that and it aids in selection. Manual J doesn't tell you what size system you need, it tells you what your system needs to provide. Load versus Capacity. Manual S is where you determine what size system/capacity.
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.
I just took a basic load calc. class for my associates degree. I don't use fancy software. And I barely needed any of it for installs and diagnostics. But even my amateur hour self can see the glaring flaws.
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.
95% of what we do is HVAC replacement equipment for existing lived in homes. Most customers don't want to replace their ductwork and rip open walls. We have to inspect the home, and run heat load calculations off of assumptions and limited data. Your methods are perfect for custom new construction or a major remodel!!
Video forthcoming on existing replacements KP
i saw one a little while back where they had no returns from the rooms. in fact half the house returned back through the kitchen.
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".
Are you recommending to NOT include CFM rates in interior rooms?
All I can do for existing lived in homes is make some educated guesses on insulation and infiltration. Then I run room by room heat load calculation. I'd love to meet a builder, engineer, or architect, that actually has all the data I need to be accurate. I've never even seen someone run a blower door test. We do a few new construction custom homes a year. For those jobs the owner does all the heat load calculations and system design.
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.
Have you ever heard of the software called heatcad? I've used it a few times for experimental purposes and would be curious, from a professionals standnpoint, if it's worth using. It includes the 3D modeling and allows for quick modifications.
Sounds hot
Do manual J calculations take into account the homes level of insulation?
Certainly
Most of the conversations are about new home designs. For an existing home, who do I call to conduct a Manual J and identify the appropriate replacement system per Manual S? I suspect if I call a HVAC company to replace my existing system they will immediately me their rule of thumb for a new system and most likely will not mention Manual J or S. What are your thoughts for such a situation?
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?
Unfortunately the competition in KY makes it near impossible to offer this kind of manual J. We only perform this level upon acceptance of bids for duct jobs. 99% of companies shoot from the hip, don’t do room by room calcs and put 6” runs in every room. It keeps us in business but the industry needs stricter standards.
Agreed, more govt regulation in this case would be a very helpful thing
@@HomePerformance or actual understanding and enforcement
Six Ton, Single Phase Heat Pumps or Heat Recovery, do indeed, exist.
12:15 I haven’t seen a residential HVAC system with a sensible heat ratio that bad in a long time. No system does 75% sensible anymore lol.
Constructive criticism. Hah!
I been doing this for 20 years I can do a manual j in my head.
The guy I had do the manual j was here for a good hour measuring. Had it done twice. First was with bat insulation and hot attic.
Then later I was more comfortable with spray foam. So re did it.
Dropped from 5 ton down to a 3.8.
Should be signing a hvac contract soon.
Just curious. How long did it take you to do this manual J?
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. :+ )
Design Temperatures are critical. ASHRAE BIN data or typically not recommended in Texas because of real-world climate change variables. In commerical design, if you ask ten consulting engineers what Design Temperature is X city, you’ll get ten different answers. Always go with someone else’s Design Temperature, when possible.
You can use actual historical data from ASHRAE, latest 2021
So not asking you to spill the beans on your client here - but am I right in assuming they're not in a town/county where this would have been evaluated as part of the permitting process?
Because based on my experience - when permits are under review, sure - no one is going to repeat the that you paid architects, engineers, etc. to do - but they'll at least do some of the things you did, and make sure numbers are at least... in ballpark and in the right format.
This is actually from a relatively progressive place, code-wise. You’d be amazed- I have another one coming that’ll floor you.
Maybe they started with the largest equipment they thought they could sell to the client, and imagined 40kW of load to sell it with.
Wow
How do you know so much😭😭😭😭
Practice practice practice ;)
The “real” Heat Load calculation. Hahahaha 😂 Like Manual J is the only method. It’s the only approved method by AHJs. I would argument that there are other reputable methods available based on ASHRAE tables. Plus, clearly there is bias in the inputs from the designer.