Manual S Deep Dive: Selecting HVAC Equipment Based on Manual J Load Calcs- Part 2 of 2

Picking up where we left off in Part 1 ( • Manual J Deep Dive (an... ), Alex Meaney shows a design where a 3.5 ton, a 4 ton, and a 5 ton air conditioner all match a Manual J load, and explores the fine points of practical applications of the 3 rules of Manual S:
1. Select equipment that can handle 100% of the humidity load (latent heat) at minimum
2. Select equipment that does not exceed cooling load by too much (15% for single stage equip, 20% for 2-stage, 30% for variable capacity)
3. Select equipment that does not exceed total capacity by too much (but this rule must be broken in some cases)
Check out Alex Meaney's trainings: MeanHVAC.com
Check out the Mitsubishi systems we selected for our forever home: • Ultimate HVAC Install ...
Watch Matt Risinger's video on the Build Show about my Manual J report tour:
• Your HVAC specs might ...
Watch Matt's video with Scott True, who's building high performance spec homes affordably: • LOW BUDGET Details For...
Learn more about the Science of Homes: BuildingPerfor...
Watch the first-ever TV series about the Science of Homes: HomeDiagnosis.tv

[@MattPetrowsky]

This isn't firehose intake. This is Goldie Locks middle bear stuff. Absolutely perfect. Keep this stuff coming!!!!

[@HomePerformance]

Thanks for watching as always, Matt!

[@yfdfireman2]

Great content! I saw a neat trick with a single stage 4 ton with TXV 2 zone system in a large house. The furnace was a 2 stage and it was capable of controlling a 2 stage condenser. To control humidity , the fan speed was set to 350 CFM/ton Y1 and after a fixed time or if both zones called it ramped the fan speed up to 400 CFM/ton in Y2 with no changes at the condenser... homeowner loved the system and said it worked great in the summer, I will say it took a little bit of digging into the settings to figure out what the installer did. I thought it was pretty slick, it would have been pure GENIUS level had the guy written down what he did and saved us 2 hours of figuring it out.

[@devonpeeples2188]

I’ve considered doing that. Could easily be done on a V/S ahu as well.

[@kevinthomas26]

10 years ago load calculation was right now its wrong and your right in 10 years another guy is going top come along and say your wrong and they will be right just like the brains behind the new A2L refrigerant. Whatever it takes to keep prices going up and we tech and homeowners spending money that motivates you guys to always be right

[@Mikecianfrocco]

So glad this collaboration happened

[@HomePerformance]

Thx Mike

[@hickorydragon8114]

Best latent sensibly explanation!

[@frankgall6]

Love this guy! Definitely taking that online course

[@moonshinewarrior]

Great info. Always look forward to the next video.

[@HomePerformance]

thanks a lot my friend

[@CajunGreenMan]

Looking forward to the Manual J course you are creating. I'm a consumer about to buy a house with no central heating/air, and I'll be putting in a geothermal heat pump. But obviously I have to see how leaky it is first (75 years old +?), plug the major leaks, MAYBE have Aerobarrier come in to plug the remainder down to .5ACH or so, and install the ductwork and whatever else, before I can even THINK of Manual J. I'm out of breath just typing all that. LOL!

[@HomePerformance]

Sounds like a serious plan, Unicorn!

[@teacherblake]

Been following all your videos for the last 6 months as we plan high performance cabins up in Montana. Looking to do some consultation with you in the near future, thanks for all the free guidance so far!

[@HomePerformance]

Happy to have helped your family, Blake

[@tweake7175]

very interesting and cool to see what goes into the calcs. over here residential hvac is pretty new, tho more and more people are going to ducted heatpumps these days. so the contrast is interesting.

[@HomePerformance]

I hope to have you show us New Zealand housing stock sometime down the road, T

[@tweake7175]

@@HomePerformance no problem mate.

[@KeneOliver]

Outstanding

[@martinp1544]

Thanks! Great Info!

[@TheJlosupra]

I love your videos. Sooooo dam good

[@johnwhite2576]

Re latent vs sensible, this is why you need a whole house dehumidifier in almost every house

[@HomePerformance]

Agreed John

[@kennethgehring-r3j]

A wise man!

[@westerncowhand7814]

Great info guys. Thanks a bunch.

[@The1JBanks]

Please talk about SHR data manual input in rightsoft. Properly sized single stage equipment is great. No expensive repairs, reliable performance and cooling/heating.

[@jimmythetech]

Great info thanks 🙏🏻

[@HomePerformance]

👌🏽 high five buddy

[@E150GT]

What's up with the two stage units that don't come in half ton sizes ? I needed 3.5 tons but I went with a 3 ton cause I was afraid that 4 ton would be too big

[@tekjunkie28]

What’s the new allowance on inverter equipment on sizing. My HDD are ~3500 and OD design temp is 15. Summer CDD are ~1550 and design temperature is either 89 or 91. My load calc comes in at 1.9 tons cooking and 28-30K BTUs heating. I’m fully electric everything. House is 1972 1158sqft and eventually I want to upgrade my single pane windows to double pane. My old unit was a 3 ton but we are removing 1 register that feeds basement. I’m planning a 2.5ton (27600 BTU) but I don’t want to be over sized. But heating would be way undersized. Please clarify what I can do. Thanks!!!

[@kevinthomas26]

what about homes with whole home dehumidifers how imperative is blower speeds and efficiency versus basic load sizing

[@denpolano]

What about having the fan on the system run all the time to increase air circulation?

[@HomePerformance]

Yes, I do recommend in high performance homes.

[@henwoopa5]

What can I do as a DIY homeowner, in a small town in Nova Scotia, with few contractors around, and even fewer design professionals anywhere near me, to get a properly sized and designed system? I am currently renovating a 110-year-old, two-story, balloon-framed, 1,100-square-foot (not including the basement which will be sealed and insulated like a crawlspace but never finished with drywall and such) house. It is a complete gut/strip/rebuild saving only the foundation, framing, sheathing, and floor boards (yes, I should have demolished it but I'm way too far in now). I built all new walls inside including interior partitions and secondary exterior walls to create a thermally-broken double-stud system. I'll have a minimum 8.5" cavity for dense-pack cellulose in the walls and will blow in up to R80 of loose cellulose in the attic. It has all new vinyl-clad casement and fixed-sash windows with triple panes and Low-E/argon. There is no exterior insulation or high end WRB but there is all new house wrap, peel-and-stick type flashing around the penetrations, and vinyl siding. I want to put all of the HVAC, including ducts, inside the conditioned space (I'll have to build quite a bit of bulkheads/soffits/chases to hide everything). The house will be all electric (no combustible fuel sources) and will hopefully someday have a grid-tied PV system with a modest battery backup. I'm concerned with heat from as early as October to as late as May, indoor air quality all year, and maybe a little AC June to September (but maybe only if it is needed for dehumidification). Thanks to all the government grant schemes I am seeing heat pump systems go in every other house without a measuring tape ever coming out. Is there any hope for me to get a properly chosen system?

[@ryanrichardson1169]

speaking of velocity and entrainment, What are y’all’s thoughts on high velocity air conditioning systems?

[@heythere61]

How do I get you to do my manual j? It's a weird situation. 1700s building going for passive house, but it will be a b&b so I want all the guest rooms and the owners suite on individual zones. Since the rooms will be individually zoned I will not be able to dehumidify the guest areas, so the units have to be perfect

[@HomePerformance]

Hell yeah, that’s my kind of weird. Send me your plans via email: corbett at buildingperformanceworkshop.com

[@Phoenix.Productions]

Thank you, gentlemen, for a great video. I would love it if you could design me a new system for an amazing project I am working on. Is this a service you provide?

[@HomePerformance]

Happy to- check this out: buildingperformanceworkshop.com/energy-modeling-and-hvac-design

[@mzzm8850]

Would love some thoughts here... Trying to wrap my head around this. With a basic block load calc, I'm estimating around 52kBTUs worth of heating required. For equipment sizing, my building science consultant (also HVAC salesman) is saying my current ductwork can handle max ~1000 CFM, so instead of sizing a 2-zoned geothermal 5-6ton system, we'll actually need to spec a 4 ton system with a backup (electric or propane). It sounds logical, but I'm a novice here trying to learn building science.

[@kennethdean4349]

4 ton equipment needs ~1600 CFM (400 CFM/ton). Your current duct system is undersized for 4 tons.

[@johnwhite2576]

I’m not seeing many specd heat pumps that are showing anywhere near parity between latent load capacity and sensible at 92 degrees F and 50% RH; more like a 85-15 split, esp variable capacity…

[@c.n.h4841]

Could you use mini splits for sudden temperature changes(in rooms or living rooms) and use the main AC system for more of a moisture removal? Is it practical? Context: an air tight house with a passive blower door scores. From a home owner and wanting to build a forever home. With general contractors experience for 18 years.

[@HomePerformance]

You shouldn’t have sudden tenp changes if the windows are properly placed and shaded, but any ducted AC only has a 30% moisture removal ability, tops. Temp is easier to lower, so that physically happens first.

[@c.n.h4841]

@@HomePerformance thank you very much I am moving to Iowa soon and purchasing land out there to build my forever home and I know during the Summers it gets quite a bit sticky and I don't want to feel that way so removing the moisture would be the best bet for me and then circulating in the air I think would be the easiest way and cost-effective but thank you very much for taking the time to reply to this and I hope you are doing great and hope you keep posting videos

[@HomePerformance]

Will do buddy, good luck

[@mikepict9011]

I find ceiling fans intolerable. Visually distracting is an understatement. Intolerable. Pco or hepa filters with occupancy sensors. Much better.

[@afrocraft1]

Rookie homeowner, so forgive me, but I don't understand the advice here. Is there any but the most extreme of scenarios in which commonly available equipment capacity won't _far_ exceed the latent? And if so, why not just focus on sizing with sensible and total?

[@HomePerformance]

That’s an excellent question, not rookie at all. Let me get back with you

[@alexmeaney2407]

The equipment capacity is published as a total, but breaks down into sensible and latent. You have to get OEM data to find out what those breakdowns are (and some don't have them available- which shouldn't be allowed but don't get me started). AND those breakdowns are dependent on the indoor and outdoor environment in which they are installed. It wouldn't be hard to find a system with aprox. 30k BTUH total but only 3k of that as latent. A latent load won't exceed 30k, but 3k? Absolutely. Long story short, when you're talking about capacity, you need to be using real capacity adjusted for outdoor and indoor conditions that's then broken down between sensible and latent. There is no central place to look that up (which is just stupid, but there it is) and I think that may be the cause of confusion.

[@afrocraft1]

@@alexmeaney2407 Ah, understood. Thanks. Two pros responding in one evening. Heaven.

[@garyreed007]

Proper return air is key, in most applications, air circulation can help offset return issues, humidity control provides better comfort, just my experience having 20 yrs in the business, certified EPA tech. Engineering Design Specialist, IAQ Certified EPA, $5 million a year project manager. 😊

[@ryansoo4000]

So for a very small (600sq') near passive home in a cold climate (zone 6B) is it better to let a mini split do the dehumidifying or to have a stand alone dehumidifier?

[@HomePerformance]

Bet money you’ll need a standalone, but try the minisplit if you like first. Dry mode (water drop symbol) increases mold on the blower wheel and housing, which increases maintenance FYI.

[@trp2413]

Sooooooooo I have a question Do the VRF Mitsubishi Mini Splits remove a decent amount of latent since they dial back and run much longer OR is the delta temp over the coil too low to remove humidity?

[@trp2413]

Question specific to ductless

[@HomePerformance]

If you put it in ‘dry’ mode then it’ll dry, BUT it increases the need for maintenance since everything in there gets so cold it’ll all be wet and moldy. Speaking from experience.

[@D2O2]

"tend to be expensive" compared to what? I would argue it's an apples to oranges comparison in product/service being delivered. There are manual Js being "performed" to satisfy permitting requirements and then there are those being actually performed for performance requirements. I think you guys fall into the latter category.

[@MrKen59]

So how does the sizing work when looking at heat pumps where you need the additional load capacity in the winter without needing resistive heat? If you size for winter use, I suspect you are oversized in the summer, and now likely have a humidity problem. Curious your thoughts. Thank you.

[@HomePerformance]

Plenty of heat pumps run perfectly down to -5 F, and keep running at lower eff down past it. No heat strips needed.

[@MrKen59]

@@HomePerformance what about sizing considerations? In the winter you could have 50-70 degree delta between indoor and out, whereas the summer it’s around 30 degrees around here. If you size for the winter capacity, aren’t you oversized in summer effecting humidity removal? I have a 3 ton 30 year old AC with an 80kbtu gas furnace. If I want a heat pump, that becomes a challenge / doesn’t it? I’m curious. Thanks so much.

[@HomePerformance]

Aha. Heat pumps are more powerful in heating mode than cooling mode generally, to do exactly what you describe.

[@aviking2614]

The next edition of the Manual S will deal with this better. Short version is this. You have to have a plan for latent capacity at operating conditions whether that involves either a dehumidifier or data from that heat pump which provides latent capacity at part load conditions, then you have to stay "within the operating range" of the equipment (which looks like it will be defined as 20-255 above min up to the max).

[@MrKen59]

@@aviking2614 thank you / looking forward to seeing the next edition.

[@Nttt739]

When you say code, are refering to mechanical building code????

[@HomePerformance]

Sometimes, but usually IECC or IRC

[@johnwhite2576]

Corbett would a continuous erv contribute meaningfully to “(traiment” sp? ) ie air flow ?

[@HomePerformance]

Hey John, an ERV won't help much with mixing, too little air moving too slowly

[@davidgagnon2849]

Would LOVE to learn all this stuff to be able to design my own system, and am very interested in these things, but honestly i don't have the time to learn it. We are needing a system upgrade and want to add an EVR to not anly deal wit getting filtered fresh air into the house, but also want to vent radon OUT. I honestly cannot trust any local companies to do the work of design and install. We've had very poor workers for just about every job we've had done at this house, spanning 34 years. Can you a) design a system for us and provide us with a name to do the work or b) give us a list of HVAC system designers that you know and trust? We're in Central Florida.

[@HomePerformance]

I can help you, David, yes. Book an hour consult at: buildingperformanceworkshop.com/video-consulting

[@davidgagnon2849]

@@HomePerformance Thank you!

[@timdestasiohvac]

Solution to your fan on or auto dilema: Bypass dehumidification.

[@HomePerformance]

Interesting, Tim- are you saying you don’t let the coil do any latent at all?

[@timdestasiohvac]

@@HomePerformance not really. There’s a great tech tip on Hvac School. Basically, you size the coil and AC to the sensible and latent loads. But the AHU is oversized to move the air for proper ACH through the HVAC filter. You blow 350 cfm across the coil like usual, but there is a bypass duct that moves the rest around the coil. The coil has a damper in front of it so when you’re not cooling, you can still move the ACH air through the bypass duct instead and there is no re evaporation of moisture from the coil,it just runs down and drains. I think you’d still need a ventilating dehu ducted into the supply duct though. This works great for large, low load houses. Check out the tech tip though. Michael Housh is testing one in his house.

[@D2O2]

Ironically, an ad for one of those unmentioned equipment sellers preceded this video.

[@HomePerformance]

Hahaha

[@OgFurious1]

If Kevin James was an hvac tech instead of a comedian 😅

[@justinsouza7812]

I think you meant kevin smith aka silent bob

[@OgFurious1]

@@justinsouza7812 his voice.. lol close your eyes and it’s Kevin James

[@ryansoo4000]

Could you do a review of HRV/ERV preheaters for cold and very cold climates? Two I've found are the Tempeff Dual Core: kzbin.info/www/bejne/bJu4gZmgjs6Aerc and the Zehnder Comfofond-L kzbin.info/www/bejne/gH-TiHyVe76fpZI

[@HomePerformance]

Interesting, Ryan- adding it to the list

[@coldfinger459sub0]

You’re on a continuous one-way ride up in quality and knowledge roller coaster. But then that would be called a roller coaster it’s more like riding a rocket

[@HomePerformance]

Thanks Tom- I feel that