Hughes Views #7 Dancing with the Devil

Ring… Ring…  
Customer: Hello, is this Hughes mechanical?
Secretary: Yes, it is. How may I help you?
Customer: Yes, I had a new system put in by you guys almost a year ago. I know its hot outside and the weatherman says it is a record high, but it just does not seem like my system is operating properly. A couple weeks ago, I know it was hot, but it seemed as if it was struggling to keep up then too.  

I do not even have to tell you guys; you know what follows next…

Customer: I think the system your team installed is possibly too small and if that is the case, I want to know what you all are going to do about it!

Ok honestly, is this not the most cringing phone call ever! Why you may ask, well for those who may have not dealt with this one, let me help you out from underneath that rock you have been hiding. This is when you know from the moment the secretary passes that call that it will not stop with anyone other than the management team, because the customer is on the defense and will not accept anyone expect the mover and shaker in charge. Then, this special trip will require a system analysis that you know you will be doing free. Next, you will be spending a solid hour talking to the client about how HVAC works in relationship to outside design bin data as if you were auditioning for Bill Nye the science guy. Once we quit playing a hundred questions, most of the time the client is totally understandable and is done playing the long game of jeopardy. Here is a tip “daily double” I like to use in this scenario, result back to the news stating that its going to be a scorcher, that usually helps the client understand that we are dealing with abnormal conditions. This usually speeds up the conversation and improve the client’s belief in your knowledge.

Customer: Chris, last summer this air conditioner struggled to keep this house comfortable, we need to go up a ton!

Boy if I had a dollar for every time I heard that! I think I have enough friends in the trade and years of experience to say that this is the reason we all want to push our load calculations over the 100% match, and that is what this article is all about. So, here is a true story for you. I have a new customer who calls, and I go to the home. It is about 78 degrees outside and humid as hell, one of those days that if you were to hang clothes on the line, you wouldn’t need a washing machine. The homeowner’s thermostat is holding 70 degrees and 65% humidity. The customer says that the house is sticky and has been for days. Now, at this point I take a walk around the house to get a feel for the construction quality, space, windows, etc. you know the drill. I ask them how old the house is? The customer says, “the house is about 2 years old, and we have not had this problem before”. Of course, I do what everyone does, I dig right into the HVAC system thinking something is wrong. Now this is an inverter system with lots of sensors. I cannot seem to find anything wrong. After the diagnostic, I ask them for a load calculation and blower door measurement results, amazingly they were able to produce. Imagine my face when those hit the kitchen table.
As I dig into the load, I notice that the house is about 117% match load for cooling. Now, Manual J says this is ok for inverters. There is no room to go bashing the load calculation, but it does make me wonder what the house humidity would be if someone would have selected equipment close to 100% match load. I explain to the homeowner the science behind load matching, but the homeowner never once asked me if the equipment is oversized. Now stop and think about that for a moment… Now stop and think about it again… Crazy right! So, I did what most of us would do, I gave it the ol’ dehum treatment! After all, you cannot go wrong with a dehumidifier in those mild and humid days.

After much thought, I concluded that we as equipment selection pros would rather explain a high humidity house in mild conditions rather than the possibility of one phone call about a home that will not keep up in extreme conditions, even playing the odds of that condition of a million to one. I will finish you guys and gals off with a challenge. If you design a house and you can match the load to 100%, and you know 100% will match the 1% extreme of that climates bin data, then why go any further? Once you get comfortable and prove to yourself that this is possible, the next time that foamed house comes your way, I dare you to shoot for that 95% load match and go dancing with the devil!

Chris Hughes of Madisonville, Louisiana is a mechanical contractor, writer, HVAC enthusiast, and founder of Hughes Mechanical Contractors and The HVAC Grapevine.  He also writes and hosts The HVAC Grapevine Podcast.  You can follow him by joining his Facebook group or by subscribing to The HVAC Grapevine Podcast.  For any questions, he may be reached at

25th Jul 2023 Guest Blogger- Christopher Hughes

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