An ACCA Approved Manual J 8th ed. may be what was offered, sold and supplied to you, but to tell you the truth, I have seen so very few, even ones provided by so called experts.
To start, what’s generally required is a room by room load calculation.
If your report says entire house or some other term that has the entire home as one great gigantic room, you have what’s called a block load. While this information may be valuable to an installer who needs to give an accurate quote, it is NOT what’s required.
What good is knowing what an entire home needs, when some rooms may account for up to 25-45% of the total load?
A complete report will show you how much is needed on room by room basis. With forced hot air, Air conditioning even baseboard heat, knowing what each room needs is by far more important than knowing what the entire home needs.
If you have a report that does NOT describe how every wall, floor ceiling and window that was modeled, and for each room, it’s NOT an ACCA Approved Manual J.
If your report has been created with software that’s NOT found in the ACCA Approved software list, it’s NOT a ACCA Approved Manual J.
If your report has incorrect information in it, it’s useless and not worth the paper it’s printed on, Regardless of who did it and regardless of how much you paid for it.
People always want to hit the “easy button”. This may even include the people you have hired to perform this service for you..
Software manufacturers have feverishly worked to simplify (Dumbed Down) their version of software so that it appeals to a larger audience.
Dumbed down may work when the home fits the generic inputs, but like the word crazy and normal, I dare you to define it.
Since you’re paying good money for valuable information, tell me, why would you want inaccurate information?
Another casualty from the Dumbed Down generation is that almost no one knows about the Manual J Do’s and Manual J Don’ts.
The list is short, may be it seems harmless enough not to pay attention to it.
The fact that it’s labeled MANDATORY must escape many.
1) People in a home add to the cooling load. What’s the correct amount to add you ask?
Its quite simple, add up the number of bedrooms you have, then add 1 to that.
If you have a 3 bedroom home, you should have no more than 4 people added to your Manual J.
I have seen HVAC contractors and local experts add 4 people to each room, or 40 in another. That’s a clear no no.
The people should be in the rooms that they might normally be in, during the hottest time of the day. Somewhere around 3PM to 7PM.
2) Heat is energy. Heat is the movement of that energy to be more precise. The amount of energy moved depends on the potential. Just like electricity and wind…
A 9 volt battery or 110 Volt wall outlet has more potential than a 1.5 Volt battery.
With wind, if there is a Low pressure system to your south and a High pressure to your north, the wind will blow from the north to the south.
The greater the difference the faster the wind. SO you ask, what does this have to do with heat. Heat moves in what direction? (Don’t say up!)
Heat moves from HOT to COLD. (Warm air is more buoyant than cold air so it rises) But heat moves from hot to cold.. Got that?
The rate of transfer is dependent upon the difference.
Slowly easing our way back, during the summer, if its 88 degrees outside and 74 Degrees inside what’s the temperature difference?
14 Degrees. Compare that to a typical day in our winter. 10 Degrees out and 65 In, that difference is 55 Degrees.
So, we now know that more heat travels when there is more potential difference, and a 55 degree difference is much higher.
Well we kind of knew this and added insulation to our walls, in an effort to slow down the heat lost. That R value also slows the heat coming in during the summer.
With only a 14 degree difference and insulation, not a lot of heat can get through that wall.
ALL of that to get to…
Your windows are arguably the largest factor for cooling loads. New windows can have some pretty amazing ratings, with a solar heat gain of only .28.
Since glass make up the largest portion of cooling loads, wouldn’t it be obvious that the most important entry in any Manual J would be to enter the glass in it with the correct values ?
I know your smart, just the fact you got this far is proof.
I can’t tell you how many people don’t (Or wont) enter the SHGC values correctly.
3) Infiltration. For heating loads, this is a biggie. For cooling loads too.
If you’re having a new home built now, chances are you might have heard the word “Tight”. It describes how your home needs to be built.
To be honest, Tight doesn’t even come close to today’s homes.
Manual J uses this term, and almost 10 years ago, to meet the LIPA Energy Star V2 program, we had to build homes to 5 Air changes. That was considered Tight.
Today, right now, NYS code requires us to be under 3 Air changes. Unfortunately, there is no term SUPER tight.
Passive House is .6 air changes. I can’t tell you how many Manual J’s I have seen that are marked Average or Semi Tight…
Using the wrong value is a HUGHE no no.
The software I train contractors with, Elitesoft allows me to enter in exactly what we are building to.
I design homes almost on a weekly basis where I’m able to dial down to exactly what is ideal for a home.
Here is a lesson I almost don’t want to give out…
Let’s see how long it takes for someone else to steal it….
While Teaching HVAC professionals, I suggest an experiment. I take out an imaginary steel or aluminum cup and let them know its full of plain water.
Right next to that cup, I put a second cup down, this cup is solid metal. I then pull out two imaginary blow torches from my holsters and proceed to heat both cups, at the same time, for 60 seconds.
I ask everyone, which cup would you be willing to hold in your bare hands. Almost instinctively, everyone in the room says the cup of water. No one ever wants to grab the cherry red metal cup…
I ask them what I will ask you.
WHY is one so much hotter than the other, when I added the same amount of heat to both?
Most don’t realize that water needs more BTU’s than almost any other substance to change a degree in temperature…
What are we made of?
Isn’t our body’s more like the cup of water?
What does our surroundings (Table, Wall, Floor etc.) more closely resemble?
If it takes time to change the temperature of water, wouldn’t it make sense that it takes time to remove it as well?
Now to drive it home.
How do we (Human Beings) Cool off… We Sweat. Evaporation is one of the best ways to cool off. More BTU’s are lost during that phase change than you can imagine…
We can’t cool off effectively if the air is humid. We need DRY air more than anyone understands.
An oversized system may simply not run long enough to remove the humidity. If it’s not running long enough on a really hot design day, what do you think happens on a 76 degree humid day?
The system turns on, cools the air down immediately, but condensation takes time.
An already wet coil can’t get wetter, so the oversized system simply leaves too much moisture in the air.
One last one (To see how quickly it spreads….)
How many days of the year would you say the outdoor temperature and humidity is absolutely perfect?
5 days? 10 days?
Let’s go big and say 10 days. 98% of the time we are trying to fix our indoor conditions because it’s not ideal outside.
Why stack the cards against yourself and not have installed what’s needed to get the job done and done well???
There are more to the Manual J Do’s and Manual J Don’ts. Following them doesn’t limit your systems capabilities, quite the opposite is true, not following limits the system.
A properly sized system will NOT be taxed during design conditions.
Manual J by design can oversize by as much as 30% for a very few design hours.
The entire rest of the year it’s oversized even further.
Add to that the fact that you just can’t purchase the exact size your home needs, so more than likely you will be getting another ½ a ton on top of everything above.
Add all of this inherent oversizing, and only this is what’s considered acceptable.
Entering information in the software incorrectly pushes the ability for your system to work during all times of the year out the window.
While none of this is rocket science, it amazes me how many experts have absolutely no understanding of how to do what they say they can do.
If you would like the complete list of Manual J Do’s and Manual J Don’ts, let me know.
If you have had a house built recently, I know of a few Towns that require the calculations for a building permit.
Chances are you can get a copy of what was prepared for your home by simply asking…
If you’re interested in having an accurate, unbiased Manual J, even if you just have a few questions, contact me any time.