Proper Heat Pump System Design (Podcast)

In this podcast, Brett and Chris from NETR, Inc talk about heat pump design. They explain the factors that affect the design of your set up, and then, they outline how NETR helps homeowners find the right design for their needs.

John Maher: Hi, I’m John Maher. I’m here today with Brett Rogenski, General Manager of N.E.T.R. Inc., a heating and cooling company in Massachusetts with a focus on Mitsubishi ductless heating and cooling products. Welcome, Brett.

Brett Rogenski: Hey, thanks a lot, John. I appreciate you having me today.

John Maher: Sure. And our special guest today is Chris Morin. Chris is a former Marine and is currently a regional sales manager with Mitsubishi Electric and owner and author of HVAC Pro Blog, where he gives advice for residential HVAC system design, quality installation, and system diagnosis. Welcome, Chris.

Chris Morin: Thanks, Johnny. I appreciate the invite.

John: Yeah, sure. So Chris, you’re a former Marine, and you actually did refrigeration… You were a refrigeration technician in Iraq for a couple of tours, is that right?

Chris: Yeah.

John: I bet that was an important job out there in the desert.

Chris: Yeah. Unfortunately, we didn’t do too much of it the first time when I was there for the invasion. But the second time, yeah, ironically, I installed a couple hundred Mitsubishi ductless systems over there when I was there.

John: Really?

Chris: That was my first taste into ductless units and heat pumps-

John: Okay.

Chris: Working in some extreme conditions.

John: I bet.

Brett: I was going to say, that had to be pretty intense.

John: So you were installing those mostly on the base and that sort of thing?

Chris: Yeah, yeah. We had a couple hundred tents we were setting up for the buildup for Fallujah, if you remember.

John: Wow. Yeah.

Chris: So it was an interesting time.

John: Absolutely. Yeah.

Brett: Thank you for your service.

Elements of Heat Pump System Design

John: So today, we’re going to be talking a little bit about proper heat pump system design. So Chris, we’ll just sort of start with you. What do we mean by proper system design and system design in general? What are we talking about there?

Chris: Yeah. So system design with HVAC really starts with load calculations. That’s the first ACCA manual. Proper system design is really defined in the code, and with ACCA around sizing the system correctly, actually selecting the right system based on the loads, and then, of course, designing ductwork if it applies to that unit.

Why Is Heat Pump System Design Important

John: And why is system design important to do before you install a Mitsubishi ductless system, or another heat pump system, or even a traditional heating system?

Chris: Yeah, that’s a great question. So I think if you don’t have the map before you enter the woods, you’re really going to get yourself in a lot of trouble. So doing the load calculation first really gives you the map for how a system needs to be selected and installed for that home. So the load will tell you how big the unit needs to be.

And then when we do equipment selection, there’s a lot of tools out there to help you with this, but you would actually select the right size piece of equipment, how it performs based on your load calculation. And then, of course, if you don’t do this process correctly, there’s a whole long list of problems out there that can rise for contractors and homeowners.

Load Calculations

John: So why don’t you talk a little bit more about the load calculation and give us some details on how that works, maybe some of the tools that you mentioned that can help you to do that load calculation and figure out what the best system is or what the right size system is for a particular application?

Chris: Yeah, sure, John. So if you didn’t know, when you go to install a system, particularly here in Massachusetts, you’re actually going to have to pull a building permit. And the building permit requires that you do a Manual J version eight, ACCA approved load calculation. So there’s many different softwares that are available through ACCA that are approved. There’s some of the more popular ones, like Wrightsoft, or Elite Software, even Cool Calc is ACCA approved. And if it’s approved with ACCA, then it’s approved to use with code and rebate programs. So there’s a lot of tools, a lot of software in order to do these calculations. And I’m going to be honest, if you don’t use the software, you’re not going to come up with the right number, particularly on the cooling side.

I, personally, am able to teach Manuals J, S, and D. I was actually taught by Hank Murkowski who wrote those manuals. And part of the exam that he gives you in order to approve is you have to do these calculations longhand. And I can tell you, the 20 or so questions he gave me, it took me well more than 40 hours at night, walking through how to do this longhand. It gives you a really good appreciation for the software that’s approved.

So yeah, you would actually be able to do this calculation in the home. Most salespeople will go out, use the software in the home, or take all the information that they need. It’s going to take too long in a larger place and go back to their office and actually do this calculation to come up with the right size system.

What Affects Load Calculations?

John: And Brett, when you go into a house and you’re doing a load calculation like this, what are some of the things that you’re entering into the software? Is it the type of insulation, is it the square footage, the size of the windows, or the amount of windows? What are some of the things that you’re checking for?

Brett: Sure. So great question. And really, ultimately, the answer is all of the above. So Chris had mentioned a couple of tools that we use. One would be Cool Calc, the other would be Wrightsoft that we use for our calculations. And we do them on all systems that we’re installing. So internally, for us, that’s a requirement that we do with every job, because sizing is important.

Oversizing, undersizing, as Chris was alluding to, just lead to cascading problems for the homeowner, which then lead to cascading problems for us. And ultimately, we want everyone happy, and usually happy comes with comfortable. That’s the whole point here.

So yeah, some of the information that we’re putting in. We’re putting… Yeah, it’s the, “What’s the size of the home? What are the sizes of the individual spaces that are being conditioned?” Usually, based on age of home, there’s some assumptions that the software will make once we enter that, about the level of insulation. Yes, the number of windows. So windows, square footage, and that sort of thing.

But those are all the things that are going into that. So the size of the space being conditioned, a couple of ways to do that. The level of insulation, how tight is this house, so to say. So is it a house that was built in 1910, or was it built in 2021? And obviously, if it’s an older home, if there have been any improvements to that since then. So that all determines the insulation level, how tight your home is. And then lets us make better decisions on what size equipment we need in each space to make it work, number one, efficiently, and number two, comfortably for the homeowner.

Issues Caused by Not Doing a Load Calculation

John: Chris, what are some of the issues that arise if you don’t do a load calculation, or don’t do it properly? What are some of the issues that you might end up with?

Chris: Oh, man. Where to start? So I think there’s a whole long list of things that come up if you didn’t size the system right. I think it first shows a homeowner if the system is overheating or under heating, if it’s not providing the right level of comfort. And then, of course, the efficiency. You assume a certain efficiency when it’s sold in the home.

And if they’re getting, with a heat pump, really high electric bills in the winter that they weren’t expecting, and of course don’t get me wrong, as it gets colder, it will be more expensive to run a heat pump. But it could be much higher than it’s expected if it’s undersized, or even oversized, because it might short cycle. So that’s the initial thing.

And then over the years, the wear and tear on the system from starting up and shutting down really starts to pile up maintenance calls and failed compressors, or with a gas furnace, cracked heat exchangers, blower motors that fail because they’re on an awful lot. So all of these peripheral things pop up as the age of the system starts to hit it, where instead of it running smooth, it’s starting and stopping. It would be getting on the highway and putting your gas pedal to the floor. Once you get to 60, you just shut your car off and start it back up. Even though that’s the way we feel we drive on the Mass Pike these days, it’s not fuel efficient to do it that way.

Educating Customers About Heat Loads

John: Sure. Brett, when you go into a home and you show a customer a load calculation like this, do they understand it? Are they appreciative that you’re doing that work to make sure that you’re selecting the right system for their size home and their situation?

Brett: Yeah, that’s a great question. And the level of understanding, obviously, goes from person to person. We don’t expect anyone to be an HVAC technician, so we usually try and take that, the load calc that we’ve done, and we usually try and break it down into layman’s terms, unless maybe this is someone that does have a background in that area or has really done their homework.

And what we really focus it on is comfort. So we kind of explained, exactly like Chris did, that, yeah, you don’t want to be getting your car up to 60 and then shutting it off and turning it on, turning it off. So we talk about right sizing that system for their comfort, also for their efficiency.

Another thing that, when we look to the cooling side, getting away from heating, that can be, again, a negative comfort situation is if people size the system wrong and it actually doesn’t run enough, and then you’re not dehumidifying the room. And sometimes every situation is different. So in a single family home, you can certainly do that, but it’s a little harder.

But a lot of times, maybe we’re talking to someone in a condo, and now they’re being insulated by each side, or they have someone above them and someone below then, that middle apartment or condo or whatever, and their equipment, if you size that incorrectly, it’s actually not going to run enough. And even though the temperature may be okay in their home in the summer, the humidity is high. And that’s because that machine, just like Chris was saying, that it’s satisfying the temperature very quickly and not running along enough to actually remove that humidity from their home. So they’re like, “Why’s my home cool and clammy?” And that’s not good either.

So there’s a lot of things. But yeah, we walk through it with the homeowner and we try and break it down to their level so that they understand that we’ve done our due diligence to give them something that’ll meet all their comfort needs, as well as work as efficiently as possible for their application.

Is Heat Load Calculation Software Foolproof?

John: Right. Chris, you said that using the load calculation software, obviously, it saves you a lot of time over trying to do it longhand. Is the software foolproof, or can you have, sometimes, issues or mistakes? Or what are some things that maybe might… Maybe it’s a user error or something that you’re not entering into the software that causes the software to maybe spit out a wrong recommendation in terms of the sizing of a system?

Chris: Yeah, it’s exactly right. It’s a calculator, and it’s only as good as the inputs as the person putting the information into it. So if you don’t put the right information in, you don’t get the right information out. And what I find is a lot of people that are new to this process, they’ll actually, let’s say, not be as aggressive, or they’ll be very conservative in the information they put in.

And when you start rounding all of these things, or you’re conservative for every window, every wall, every ceiling, you start to add all of this extra heat loss or heat gain into the home that’s not needed, and you oversize it from the start. So yeah, that software is just as any other calculator. And really, we have to concentrate on educating the salespeople and the system designers on what the right input is and why you need to be aggressive with these inputs, because there’s already rounding and oversizing built into the software to start with.

You Need Quality Inputs to Get the Right Calculations

John: Sure. So being more specific, making sure that you’re getting your measurements correct and being very exact with all of your calculations, that’s important.

Chris: Right. Right. That’s the number one thing. And then, of course, there are some obvious things that impact the load the most. So the few things that impact the load the most on the heat loss side is, of course, design temperatures, which is clearly defined, yet not always followed. And then, of course, the insulation level, because particularly on large devices like a ceiling, it’s a large surface area in a ceiling, so you have a flat ceiling and a colonial or a cape, and if you don’t get the R value, within reason, then it could really drastically change your heat loss.

Of course on the heat gain side, on the cooling side, windows and infiltration, and believe it or not, internal gains can impact the load enough to change the size of the system. And really, guys just miss it. They didn’t enter the window, or they miss a skylight, or they put too many people in a home, because the homeowner likes to entertain on a Friday or something. Even though that’s what happens, that’s not how we size a system for comfort for the house.

Finding the Best Design for Your Home

John: In terms of the system design itself, is there only one best system design for a given situation, or are there potentially multiple types of designs that would work well for a given home?

Chris: Oh, man. Yeah. I think the best design is the one that’s going to provide the most comfort at the most efficient point. So that can be drastically different depending on the comfort level of the designer and, of course, the homeowner. So just picking on Mitsubishi here, given my background, we have a wide array of indoor units, and depending on the style of indoor unit, the design could be impacted heavily.

So if you want to use all, let’s say, wall mounted ductless systems, how you apply those ductless units will vary differently compared to mixing that with ceiling cassettes in ducted systems. And of course, the size of the unit will be different too if you have duct work in an attic versus no duct work at all with ductless units. That impacts the load calculation. So yeah, every single home is different, and then what homeowners are comfortable with installing their home can also impact that design as well.

How the HVAC Equipment Affects the Calculations

John: So as part of the load calculation software that you’re inputting what the system is going to be that you’re installing, and it’s telling you whether or not that’s the right size system for the application?

Chris: Yeah, that’s a level of it, meaning you have to know how you’re going to heat and cool the space. So is it going to be ducted or ductless? Is it going to be a boiler, or a furnace, or a heat pump? So that level of designing based on comfort and how you’re going to deliver that needs to be known in order to enter the load calc.

But a lot of the stuff is just the house specifically and the direction those devices face, and like Brett was saying, the infiltration of the home or how well it’s sealed, how well it’s insulated. Those are the key things that don’t change based on your design. So it doesn’t matter if I put a ducted or ductless system in, the heat loss and heat gain of that house is going to be the same if you exclude the gains and losses on the duct system.

Making Changes to the Design During the Installation Process

John: Brett, when you go into a house and you’re already maybe starting the installation, do you sometimes have customers who say, “Hey, now that you’re in here, actually, could I add another unit to this room or that bedroom,” or something like that, and now all of a sudden it changes the system?

Do you have to go back to the drawing board and do another load calculation and try to figure out whether you can do that, or if you have to make other changes in order to compensate for it?

Brett: Sure. Yeah, that does happen on occasion. And yeah, I mean, we kind of go back to the drawing board, and it’s really situation specific. Sometimes, depending on what the customer’s hoping to achieve here with that change, sometimes it can be accommodated pretty easily, there’s enough flexibility there. Other times, it can dramatically change it, and we have to really tap the breaks with them and say… A lot of times, it comes back to asking them, “What are you trying to achieve here?” “Yeah, so let’s stop talking about pieces and parts and hardware. What is it that you want to change, and why do you want to change it?”

And listen, at the end of the day, they’re the customer. We’re here to meet their needs. In a situation like that where it’s a more dramatic change, yeah, we probably do have to go back to the drawing board. And for us, that means restructuring the entire system, potentially. And for the homeowner, that means maybe altering their investments.

But we’re always willing to do that. It’s their home, we’re here to serve them, but we won’t just go, “Oh, yeah, you’re sure you want another head in the living room? Yeah, here, we’ll just smack that up, call it close enough.” Because that’s going to end up leading to an unhappy customer, one way or the other.

How Rebates Can Affect System Designs

John: Right. Yeah. Chris, any final thoughts on system design and how it impacts both contractors and customers?

Chris: Yeah, thanks. I think a lot of the contractors here in Massachusetts really get limited in their design process because of the rebate program that’s available locally. There’s a lot of money and a lot of financing and a lot of opportunity on the table, and they really focus in on those systems that only qualify for that, and they don’t broaden their horizon to look at all the systems that might qualify for that.

They get very comfortable in certain models. If they were to open up and look at everything, I think you’ll find that there’s a lot of mix of multiple systems, multiple units, many ways to heat and cool a home that’s not just the same system day in and day out. And if we look at sizing the system correctly, making sure that the system will actually deliver the BTUs that’s needed at those designed temperatures, that’s more important than if it qualifies for a rebate.

Don’t get me wrong, with some of the financial pieces that are available, that project may not happen if it doesn’t qualify for rebate. But you’re much better off installing a system that’s going to work efficiently and provide the comfort than it would be to get X dollars back.

Helping Customers Find the Best Design for Their Needs

John: So that’d be something for contractors to make sure that they’re explaining properly to customers and homeowners that, “Hey, look, we have another option. We think this might be a better option for you. It’s not going to save you any money. It might cost you more, because it ends up not qualifying for a rebate.

But in the long term, this might be the better system for you. We don’t have to do it, but it’s something for you to consider,” that sort of thing. Do you have those conversations with customers, Brett?

Brett: Yeah, we do. That’s actually something I’m really proud that we do, because, let’s face it, the easy thing when someone comes to you and says, “Hey, I want to put in a whole home ductless system, because there’s a really big rebate out there, as well as some very long-term zero interest financing available to me.” I mean, the easy thing to do is say, “Sure, sounds great.” But that’s not always the right thing to do. Certainly, there are plenty of applications where it’s a wonderful application.

But we look at it, to Chris’s point, we try and be holistic with it and talk to the customer about, “Okay, let’s not talk about pieces and parts and solutions. Let’s talk about, what are you trying to achieve?” And that may become some sort of a mix system. It may be a different solution, or it might be exactly what they called us therefore to begin with.

But we want to have those conversations. And then I like to always say, people are all adults, they can make decisions, but we’re not doing our job unless we let them know what all the options are and why one may be better than another. So we’re actually pretty proud that we have those conversations.

And we’ll have, a lot of times, people looking for ductless whole home rebates and that sort of stuff is why we meet them. And then we talk about their situation and what they’re trying to achieve. And we may end up offering maybe a partial home, or maybe an entirely different solution, but again, based on their feedback of what they’re trying to do. So it’s always tempting to take the easy path, but it’s not the right thing to do. We’ve been doing this for 34 years, we want to do it for another 34, so our reputation matters to us.

John: Absolutely. Yeah. All right. Well, that’s really great information, Brett. Thanks again for speaking with me today.

Brett: Thank you so much. I appreciate your time.

John: And thanks for joining us again, Chris. And where can contractors or other people in the industry find out a little bit more about you and follow you?

Chris: Oh, thanks, John. Yeah, I appreciate the time as well. If you’re looking for information about system design, quality installation, and, of course, system diagnosis, you can find me at, or out there on YouTube, Facebook, Twitter. Can’t get away from me once you find me.

Contact NETR to Talk About Heat Pump Design

John: All right. Well, thanks again for joining me, Chris.

Chris: Thanks, John. Thanks, Brett.

Brett: Thank you.

John: And for more information, you can visit the N.E.T.R. website at, or call (781) 933-NETR. That’s (781) 933-6387.