Is a Load Calc Without a Blower Door Pointless?

Over the last few weeks I have been asked the same question A LOT:

In regards to retrofit, why bother with a load calculation if you don’t do a blower door and duct leakage test?

Sometimes accompanied by this:

Without a blower door test, the load will vary +/- 70%.1

Let me save you from having to read the rest of this article (seriously): It is my strong opinion that a visual inspection can identify the vast majority of homes with serious leakage issues. BUT, once you have identified that a home has serious leakage issues, you likely need a blower door test to properly quantify the problem.

Also, for clarity, I am not talking about new homes. I firmly believe that all new homes should be blower door tested. What’s the difference? With a retrofit, enough time has usually passed for the telltale signs of infiltration to emerge.

With that in mind, my answer to the question above is this: for most homes needing retrofit/replacement, you don’t need a blower door test to do a good load calculation (assuming a good visual inspection). And those homes that do need a blower door test are generally identifiable. Also, not for nothing, doing a load calculation with baseline Manual J “Loose” infiltration and comparing the results to the existing equipment can be a good first step in getting that blower door paid for. Example:

“Mr. and Mrs. Homeowner, we’ve run the numbers and using the leakiest setting the code book has, you shouldn’t need more than a 60,000 BTUH Furnace. The thing is, you currently have a 120,000 BTUH furnace that you said runs all the time on a cold day. While there are a few possible reasons for this, the likeliest is that your house is much leakier than it should be. To put things simply, you’ve got some big holes in your boat. We’d be happy to sell you a really large bilge pump to deal with it, but it might be better to fix some of those holes.”2

… transition to a conversation about your weatherization services, a recommendation for a weatherization contractor that you’ve partnered with, the low-cost state program that will help address the issue, or whatever path you’ve identified to deal with the underlying issue.   

So there. That’s my answer. You can stop here. 

Or you can take the scenic route just for fun:

For the scenic explanation, we are going to make a weird turn. We are no longer HVAC and Building Science professionals. We are now in the business of selling clothes online.

We’re going to look at a few business models for our new online clothing retail business. This business will attempt to eliminate the need for customers to pick out the right size themselves. We’re going to do it for them. Why? Because we’re tech disrupters! Inventing solutions to problems that don’t exist using other people’s money is what we do!

Business Plan #1. The Trade-in/Trade-up Garment Trading Post. Customers send us a pair of pants or a shirt that has worn out and needs replacing. We read the size from the tag, ask the customer no questions, and sell them something of the same size from whatever brand we like. We don’t know if the customer has gained or lost weight, or if those clothes currently fit them very well, that’s what they’re getting. Even if the pants are obviously split in the seat or the shirt is stretched out, they get one “just like” what they had.

Side note- some of you may not appreciate the level of dissatisfaction we would experience with this. If so, you are likely a dude currently wearing size 32/32 jeans or thereabouts. If you are a decent amount shorter or taller than average or a person in possession of a couple of curves, you can skip the next paragraph while I explain the scope of the problem better.

I am a man of… generous proportions,3 so I’ve had some fit issues now and then. A few years ago I had to work a trade show where everyone was supposed to wear new shirts the company was purchasing. I wore a company shirt pretty much every day at the time and they had my sizes, so everything should have been fine. Management was having some trouble settling on their new look so the shirts were going to be rush ordered and priority shipped directly to our hotel. On the day before the show, I set up the booth, came back to the hotel and picked up my new shirts. I checked the label and they got the size right. Cool. Except obviously not cool or why would I be telling this story? Now, it’s the morning of the show and… have you ever seen the movie Tommy Boy? If so, you know what’s coming next. I put on the button-down shirt and it’s “fat guy in a little coat” time. I didn’t even get to see how far away from buttoning it I would be. The damn shirt literally ripped as I brought my second arm through. No kidding. I rechecked the label. Yup, it’s the “right” size. I try one of the polos. I could barely get my (admittedly outsized) head through. I end up at the booth with an old company shirt I already had with me. When I get there, I see that I’m not alone: one of my coworkers was giving EVERYBODY two backstage passes to the gun show, another had fallen back on an older shirt like me, and that was the day I found out that a third had her belly button pierced. If you’re curious, it was all Port Authority Corporate Wear. Nobody knows nominal sizes suck better than I do, but (at least at that time) they took that to a whole new level. Beware.

Okay. So… There are bound to be tons of angry customers with The Trade-in/Trade-up Garment Trading Post. Safe to say it’s a bad plan.

Business Plan #2. The Big Brother Clothing Company. I’m not talking hand-me-downs here. We hire a bunch of smart data scientists, and they build an algorithm that will estimate needs from data we can buy about our customers online. Age, sex, ethnicity, income bracket, geographic location, and who knows what else can be shown to correlate with size, brands, style, etc. We still aren’t asking any questions here. It’s all just data we buy about our customers online. This would probably work so well on average that it would be scary.4 But some of the failures would be SPECTACULAR.

I would likely be one of those failures. I am proud to say that the internet still hasn’t figured me out completely. I’m a big gift giver and have a tendency to repurpose things for little building projects I play around with (why just buy it when you can make it for twice the price and so much more time?). Anyway, these tendencies have led to such varied online purchases and google searches that one of my recent Amazon “recommended for you” lists consisted of survivalist rations, a pair of safety glasses, and a menstrual cup. I don’t know what they think I’ll need that particular combo for, but count me out (absolutely true by the way).

In the end, this business plan might (admittedly hypothetically) have a chance of being significantly more accurate than plan #1 ON AVERAGE. But it would have a much higher incident rate of catastrophic failure.

Good on average or not, I don’t think a bunch of 1-star reviews showing people standing in one leg of their new pants would be good for sales. Probably not a great plan here either.

Business Plan #3. The Thousand Words Clothing Company. We have customers take a selfie wearing some reasonably form fitted clothes while holding up a common object for scale like an 8½x11 piece of paper.5 We then hire experienced (or well-trained) people to identify what would best fit this person. Are things always going to fit perfectly? No. Pictures taken at weird angles could be deceiving, customers taking pictures with baggier clothes would be a problem, and some of our more generously proportioned customers might just be difficult to judge. But with an experienced/well-trained team, we could probably have really good customer satisfaction numbers.

Not a terrible business plan. Not ideal given the creepy factor (though I always underestimate the public’s willingness to share things online), but the most sustainable so far.

Business Plan #4. The Hub and Bespoke Clothing Company. This one is simple: to heck with it, we’re going to need our customers to see a tailor. We’ll get all of those measurements- right down to the leg that’s  ¼” shorter than the other and we will create a garment that fits you like one of those high-tolerance metal fabrication videos that I can’t seem to get enough of. Will they have to pay for the tailor? Yes, but such is the price of perfection.

This one is sort of a thing already. I just bought a few custom shirts like this. The company I bought them from will work from measurements you do yourself or get from a tailor. In my case, I sent them a shirt that was already tailored and I like the fit of for reference. I have high hopes, but they won’t be in for a while.

Okay. We’re done with our hypothetical clothing companies, and while you can see where I’m going with all this from a mile away, it would be weird if I didn’t bring it home.

Each of these business models is a stand-in for the prevailing methods of sizing a system.

The Trade-in/Trade-up Trading Post is standing-in for what is an all to common practice: “like for like” replacement. And considering how often systems that died after 8 years old (for example) get replaced this way, I don’t think my jab at replacing things with overwhelming evidence of sizing issues (the split pants, etc.) is unfair at all. Are there people looking for these signs and at least trying to act accordingly? Sure, but I would not say they are anywhere near the majority of “like for likers” in my experience.

As for the any brand /nominal size problem, that doesn’t exactly have anything to do with brand In the HVAC world. It’s more about the changes in technology over the years and the shifts occurring in actual capacities, particularly latent (another rant for another time). And yes, I understand that if you’re reading this, you already know it’s a bad idea to size like for like but since some are comparing not using blower door/duct leakage to like for like, I wanted to establish a baseline. Anyway, like for like sucks. Don’t do it.

The Big Brother Clothing Company is, of course, our analog for emerging technologies attempting to perform load calcs from mineable data. And while I will admit that some of the tech looks promising (using energy bills, data loggers, and on-site scanning technologies in particular), others (like satellite images, square footage from real estate, and age of the home from public records) have some big inherent flaws. For the record, I think the on-site scanning stuff has one foot in this “business plan” and one squarely in the next as it involves being on-site, but I lumped it in here as it is still emerging tech.

The Thousand Words Clothing Company is, you guessed it, a good ol’ site visit and visual inspection with Manual J. Is it perfect? Well, considering nothing is perfect,6 no. Is it subject to swings of +/-70%? Absolutely not, assuming you have two eyes and an ounce of common sense. Does it take extensive training? It certainly takes a decent amount, yes. Hell, that’s part of the reason I have a job/business.7  Will I please stop with the question/answer format? Yes, sorry.

Lastly, if for no other reason than symmetry, I should state for the record that the Hub and Bespoke/tailor model is our blower door and duct leakage testers. Like a tailor, it’s the best way to go if you can afford it. But if you can’t, should you just give up? Or worse, should your customer be forced to settle for terrible quality when they could have (and could have afforded) something better, if not perfect? Yeah… I’m going with no on that.

So here’s the million-dollar question: What if the Thousand Words and Hub and Bespoke Clothing Companies were divisions of the same company? Or had some sort of partnership arrangement? What if our sizing evaluators at Thousand Word identified situations that would present obvious problems for them and instead of recommending something that they knew was likely to be flawed, they at least recommended that the customer proceed with Hub and Bespoke instead?

That’s what I think the most reasonable approach looks like.

Well, ideally anyway. These days it would be unsurprising to see them start recommending tailored services to literally everyone (including those that most likely don’t need it) because their profits are better on the higher-end product. My experience with corporate America tells me that they might even drop the observation model completely for one of the worse options to bolster their claim that tailored is the only true way to go. Which is too bad, those sorts of models tend to burn themselves out in the long run. Consumers start to get wise to that kind of stuff for a variety of reasons.

At the end of the day, the claim that “without a blower door and duct leakage test, load calculations are useless” is predicated on the idea that people can’t identify situations where infiltration could be a big problem. And that’s rarely true. There are dozens of indicators from dust discoloring attic insulation, to daylight shining through gaps and penetrations in rim joists, to just checking your load outcomes against system size and the homeowner’s lived experience.  

I’m not saying those things (among lots of other observable elements) are particularly good at quantifying the amount of leakage in a home, but they are good at qualifying whether a home is very leaky. So let’s not (warning: dual-cliche conclusion incoming) throw the baby out with the bathwater and let perfect be the enemy of the good. 

Do a load calculation on replacements. Blower door and duct leakage tests will give you the best results, but the absence of the best doesn’t mean you should settle for the worst.8

  1. Oooh. A statistic. It must be right… Reminds me of the Mark Twain quote about “…lies, damned lies, and statistics.” +/-70% is the range you might find in a heating load in a cold climate IF you compare an ultra-tight house to a house that can barely hold 50pa of pressure. If that entire range is in play after observing a home, you need to get your eyes checked. Or learn how to have conversations in good faith.
  2. The leaky boat analogy is likely something many of us have come up with on our own, but I heard it first from the excellent HVAC Tech Trainer, Ty Brannaman.
  3. People sometimes get weird when I just say I’m fat.
  4. Let’s all be thankful that I had the editorial competence to delete the overly long rant about The Man and Big Data.
  5. Yes. I hear it. Let’s collect a bunch of pictures of people in tight clothes holding up paper like kidnapping victims. Complete creep show. But it works with the point I’m making… Which I swear I’m getting to.
  6. Well, except maybe the end of ‘It’s A Wonderful Life.’ That may be perfect. I am not generally a very emotional person, but when I hear the sentence “To my brother George, the richest man in town.” The waterworks come on. Every. Damn. Time.
  7. Aha! You’re biased! I knew it! Okay. Sure. You got me. Congratulations. But if we’re throwing things out because of bias, I don’t need to write this at all. Because, let’s be honest here, the ideas I’m pushing back on come from sources that have- generously speaking- at least as much bias as I do. And I will (and already have) admit that some of the technologies show serious promise in replacing many of the things I currently teach. Oh, and guess what? When that tech proves itself and becomes available, I’ll start teaching that (duh). I mean, I read (and hated) “Who Moved My Cheese?”
  8. If you STILL disagree with that sentiment, start researching the accuracy of blower door calculations compared with tracer gas testing and ask yourself if not being perfectly accurate is a reason to not bother.