Your HVAC specs might be COMPLETELY wrong: Manual J Training

Check out Corbett and Grace Lunsford at @HomePerformance

Subscribe and follow my Podcast on Apple or Spotify!

Sign up for our twice-weekly newsletter:

To sponsor a video or advertise with us visit:

Huge thanks to our Show sponsors Builders FirstSource, Polywall, Huber, Rockwool & Viewrail for helping to make these videos possible! These are all trusted companies that Matt has worked with for years and trusts their products in the homes he builds. We would highly encourage you to check out their websites for more info.

[thezfunk]

I finally got a new furnace and AC installed. I went with the young guys who just started their own company who did the actual load calcs for my house instead of just eyeballing it based on 'experience' or the old system. I had a 4 ton AC and 88, 000 BTU furnace. Everyone else wanted to replace with a 4 ton with a 110, 000 BTU furnace. The guys I went with asked me details on the house, what improvements have I done, what insulation have I installed and witnessed installed. What air sealing have I done, etc. They sized me at 60, 000 BTU with a 2 ton system. I was really, really skeptical since they were the outlier but they showed me the numbers. It helped they were the cheapest since they were installing the smallest equipment. I had a 30 year old furnace and a 40 year old AC so anything newer would be an improvement and so far, everything they said has proven true. We'll see this winter but so far so good.

[andrewfischer]

I’ve always enjoyed Corbett’s videos, they’re so helpful and informational and he’s such a energy geek like me. I’m surprised he didn’t get into more details about orientation at the house N, S, E, W. With the manual J software we can easily simulate how the heating and cooling loads change by virtually changing the orientation of the house. The exact same house facing north south east or west can require different heating cooling loads They can vary as much as 25, 000 BTUs depending on which way the house is facing. This is why I recommend running these calculations before the architect and builder Have filed plans for the building permit. An energy and comfort conscious buyer owner might be willing to change the orientation of the house to reduce the energy level by 20%. Manual J software can even take into account roof overhangs and tree shading for more accurate results. For new construction is pretty rare to have tall meaningful trees close to the house. But for older homes in retrofits it’s very common and can result in a half ton more difference in the size of the condenser and coil. I was also surprised Corbett didn’t go into details about CFM versus BTUs. Manual J software can give a room by room breakdown of CFM’s delivered for heating and cooling season. This is a critical detail for the HVAC installer needs to use the maximum CFM of either heating or cooling. And make sure the ductwork and registers are sized properly to deliver this predicted CFM. Manual J software can also take into account whole house ventilation systems to deliver the desired ACH. It’s also important to note that anyone can learn how to design manual Jay reports with the right training. Builders can learn it and do it themselves. HVAC designers and installers can learn it and offer more value to the builders. More architects need to learn this technique as well. Most city and county building departments now require manual Jay reports before they will issue a permit for the house or a new HVAC system. And if I’m the owner or buyer I would like a thorough level of details and no more of this rule of thumb BS. Also he didn’t speak about zoning very much. Manual J software can and should also model zoning the house based on multiple zones for a single set of equipment. Or multiple sets of equipment per her house with each equipment serving one zone. Manual J can also be used for what if scenarios like, what if I used ductless split units versus traditional unitary equipment with sheet metal ductwork. They can also run what if scenarios showing flex duct versus metal duct. They can also show what if scenarios that show the difference with or without fireplaces and how many fireplaces. I use Wrightsoft manual J software. But there are a few others that are good including Elite. All manual J software Hass to know the ZIP Code of the building and uses that to get accurate weather data to predict heating degree days HDD and cooling degree days CDD. These are critical parts of the heating and cooling load calculations. The HVAC designer can vary whether you want to design to the 90 percentile (not recommended ) 95 percentile which is what I consider the sweet spot. Or the 99% percentile as Corbett went to in this example. You won’t take a big a hit designing to the 99% in a Matt Risinger new construction tight, energy efficient house. But 99% would be overkill in a retrofit of an older home.

[erickessler]

Matt,
Don't apologize for a long video!
This was an amazing and critical subject with Corbett! Love ya bro, so keep these extremely practical videos with Corbett, Scott True, Steve and Jake for long format!

Cheers, Eric
😊

[erickessler]

Matt, Corbett,
This is a stunningly gr8 edu video! Thank you both so much !
At the 18:00 point, Corbett used SketchUp to create a simple depiction of the home. Outstanding!

Wouldn't it be IMPORTANT at the same time ... If we included "Strategic Window Placement" & "Roof/Soffit Overhang, " so we could also refine the roof overhangs with respect to the sun on various summer & winter scenarios?
Energy Vanguard did exactly that for me on my Virginia home and we increases my front south facing dormer & porch overhangs.

Corbett's AED points at 23:15 about west face windows will be especially critical for me on our new NC home design, with it west & water facing front-door side. 🤔

Thanks AGAIN for a brilliant video!

Cheers,
Eric

[allanlindsay]

Having lived in a 1970 built house for the last 20 years where NONE of this planning work was done I can tell you that no matter the price point of the build this is critical and actionable information. For those viewers who are "just a homeowner" take these details and think about it carefully before you have your H-VAC (I'm in Illinois that's how we say it :) ) replaced. Maybe you need to have your duct system tweaked to avoid hot rooms and cold rooms. Maybe an ERV is worth the retrofit. Great information here.

[Fulloctanegarage]

I own a new construction heating and cooling company that does primarily single-family residential. We start about 12 houses every day. Probably the biggest challenge that I have seen is getting accurate and current information from the builders about the product that they are building. We will often see that Building materials or processes have changed especially due to the supply issues of late. Situation is like not being able to get tech shield and so they just leave tech shield off houses for a couple months but they failed to notify anyone lol. We sent out builder survey sheets every six months to all of our builders every six months where they enter all the current specifics for all of the factors that will affect our HVAC load a.k.a. windows, insulation package etc. it’s always a work in progress. We run plot specific loads on every house that we do. Actually that’s probably another good point, using generic house plans and not taking into consideration the orientation of the home on the lot can make up to a large difference on a six or 7 ton home because of window exposures.

[NINExx]

Can't recommend Corbett's YouTube channel enough, his house build is on a whole different level.

[CajunGreenMan]

This! is! perfect! I plan on installing my own geothermal system, and I am not trained as an HVAC repair man. This is exactly the deep dive into manual J that I've been wanting! Keep up the great work!

[hubercats]

Great video! Thank you. One comment follows: When discussing what I’ll call “effective square footage” I think what’s really important to convey to viewers is that it’s the volume of the house that gets heated or cooled, not the square footage. Given the volume of the house (cubic feet) one can then divide by the ceiling height (feet) to get an “effective square footage” (feet squared) which is what the Manual J calculators require. As a caveat, I’m not an HVAC specialist (rather I’m an electrical engineer) so I may not be thinking of this problem correctly. I hope this comment is helpful.

[mattgirgenti]

I am smack dab in the middle of this so the timing of this video was PERFECT! I have a bunch of twists since I am comparing a VRF zoned solution versus a Geothermal (pond loop) solution. Apples and Oranges, BUT the both are viable and our personal long term goals come into play. Oh, and we are about to start a remodel of the 70's ranch house (vetting contractors now) and build a new office/in-law suite+garage workshop at same time. I am not sure I could add more if I wanted to (except solar and 2nd well, which is already in process. ha!)

[davepetrakos]

Corbett is a composer for the music in the mechanical room. One of The Best 38 minute videos.

One take away is even though we need to plan on 100 yr flood, we don't really want to have huge equipment for the heatwave that seldom shows. With humidity it is more efficient for a slightly smaller system to run longer than a larger system cycling more frequently

[MegsCarpentry-lovedogs]

Wow! I came across his channel organically just by looking at passive home inspired building that emphasize air tightness and water....so wonderful to see your support with this man! 👍💯🇨🇦

[CommonSenseFishing]

One thing I'll say as a hvac business owner. With system sizing sucks big time if you put in one too small. Put one in too big and sure you'll have some issues but not as pissed off a customer as one who's home can't cool below 78 on 110 degree day when their neighbor can get down to 68 on a 110 degree day and both homes are similar. With that being said, don't be lazy. Do a load calc. But ways you can avoid screwing up load calcs is installing variable speed equipment and proper ducting.

Also. When you do a load Calc for 99 degrees but we have like 40 days or more over like 105 this year in Central valley CA. Dry humidity. Don't want your system running too long. Dry the air out terribly.

[richdobbs]

It seems funny that here in North America we design for a couple of hours of extreme conditions instead of what's most cost efficient through the year, and whether the burden of system failure is tolerable or not. For example, you aren't allowed in the code to rely on plug in space heaters even if you have more than adequate power supply. But, AFAIK, you could use a wood fired stove which isn't any more convenient or safe. For cooling load, it really matters what the distribution of hot days are. If it was just 1% of the time I could just tolerate failure if the rest of the days were okay. But not if that also failed for two weeks every summer, or it resulted in mold growing during a muggy spell.

[totallybonkers]

I thought Matt was going to say "Let's back up a second, you're not an engineer?" 🤣
Let's hear it for the musicians! They never cease to amaze me with their intelligence! I know many who moonlight in other professions and are the best at everything they do!

[Nick-bclm]

I am one of the many in the humid south east Texas that has their duct work in a hot 140 degree attic. Been doing a lot of youtube, research, learning, and note taking. House needs a new roof along with a new efficient AC/furnace system. Didn't know there were 3 different run cycle units. Not my "forever home" so on the fence about a metal roof. Tonight, saw Matt's roof build with cool-vent panels. Will accept shingles or metal roofing. One thing I am for sure doing is spray foaming the attic.
My folks had their 3 car garage spray foamed, and installed a mini split system. I'm sold on the foam and mini split. Will be adding one to my garage as well. Lots of good info. I have to find an auditor to do load calculations, someone that doesn't work for HVAC company. That way they can't tell ME what size of a unit I need to install. During these past hot few months, electric bill has been 400 bucks, for a single story house. So I am reading and looking to see what all I can do to make it low as possible. Changes are coming very soon.

I am enjoying all this free info yall share. Down the road when I plan to move west, (centeral Texas) makes me really want to build a home so that its built right from the start.

[timdestasiohvac]

An encapsulated attic is not considered a conditioned space. It is a "semi conditioned" space because we are not trying to maintain 75/50. Even though it is inside the envelope, it should not be treated the same as the living spacr. In Wrightsoft, you can select the ceiling material as an encapsulated attic, set the roof deck R value, and the expected attic temperature (usually 85 degrees). There is a small transmission gain and duct gain from an 85 degree attic into a 75 degree space.

[Grossinspec]

Great explanation. Now to do my houses manual J.

[garyhiland]

Corbett's video on HVAC static pressures is the best on youtube. Just finished the BS and Beer seminar in Kansas City last week and I told them they needed to get Corbett for next year's tour.

[boby]

I’m glad he straightened Matt out about including the size of the conditioned attic. Matt always acted like he got that square footage for free (it’s not free, you have to condition it); is it better than insulated ductwork in a hot attic ? Absolutely. So glad I live in an area where 95%of the homes have basements. Corbett did an outstanding job on explaining how manual J should work 👍. Ductwork design manual D is every bit as important as manual J . Size the ductwork correct, install the supplies in the area of the windows and install returns in every room but for the bathrooms and kitchen (Life will be good whether you have a single stage, two stage, VRF or VRV).