"I consulted my architect and he does not have any issues with the refrigerant lines above the roof deck either."

I would trust my HVAC guy on this issue more so than an architect but that would be just me. Have you asked other HVAC contractors for pricing and their thoughts?

What is the climate? What kind of insulation and roof deck? Is the total run only 15ft.?

I suspect future repair of the line set would be expensive.

Sounds like a reasonable request, so did the contractor give any explanation why he refuses? Ask him why, and to avoid having him blow smoke up your....ah nose I'll give you some information for reference.

Compressor oil circulation is critical and velocity in the lines must be maintained to move the oil, usually around 1200 feet per minute or more and the efficiency loss must also be kept to a minimum at 3% or less, either will drastically effect the life of the compressor and even destroy it in short time. The line set length will determine the velocity and efficiency loss but the diameter of the lines will compensate for the length to a certain length before velocity drops. Simply put you increase tube size to compensate for length while maintaining velocity of the refrigerant in the tube, but a little complex in practice so the manufacturer's installation guide is required.

The installation guide addresses length, size, rise (height) and refrigerant charge to make it simple again. I took a quick glance at a new 3 ton A/C unit interconnecting tube guide and see it max's out at 300 feet with a 90' rise using the maximum allowable tube size to maintain velocity. Do you live in a 6 story house? If not I really don't see a concern to your request and may think he's trying to save on material to pad his pockets.

So ask him why, and also ask him if he will run a PVC conduit in the roof to pull the line set through. A/C lines will create condensate even when insulated if any moist air is able to come in contact with them and destroy your ceiling, insulation on those sets aren't perfect. And what if the set needs replaced for some odd reason. A kink from Sloppy insulation or ripped insulation on the line set from the same sloppy insulation? Don't give him the opportunity to destroy your home, and fire him if you detect lies, lazy sloppy workmanship or greed.

This is in Southern California. The home is single story MCM with very low slope shed roof. The roof deck is 2x6 T&G with 8" XPS rigid insulation and rubber membrane roof. We understand future repairs would be expensive. That would be the case for the plumbing pipes as well. The total run would include another 40' max in the attic.

The HVAC vendor said repair would be expensive if the lines were to leak in the future and he would do what we ask if we sign a paper saying he is not responsible if the lines leak.

I forgot to mention I also called and talked to the inspector assigned to my area and she told me it is not against code to run the refrigerant lines on the roof deck under the rigid insulation.

Another option would be running the line set on top of the roof deck and wrapping it with Flexible EDPM pipe insulation. Water proof, UV resistant, requires no outdoor weather protection, is paintable and good up to 300 degrees. Or a mineral wool pipe installation but would require weather protection such as an aluminum outer jacket. I used fiberglass pipe installation with aluminum outer jackets in central Texas on commercial flat roofs per a HVAC engineers designs in my day so I know it's durable. Is it safe to say the condensing unit is at the back of the house? Any wrap would look just fine since it's rubber membrane roofing.

You only have replies from amateurs, people not in the industry, on this site. I'd follow the advice of your HVAC contractor. Running it on top of the roof means punching holes in the roof, that's not something I would do on a mostly flat roof.

The fact that something isn't precluded by the building code doesn't mean it's a good idea. Nor is the fact that it's one alternative allowed by the building code mean it's a good choice.

@kevin9408,

Thanks for the advice. I think running above the roof surface exposed is an option. The condenser is at the back corner of the

@Elmer J Fudd,

Understand what you are saying, but we already have roof penetrations elsewhere and we do not want soffits inside. We don't get much rain in SoCal.

I assure you lc I'm not an amateur. My resume is extensive and crossed over into many different fields over my career but I'm retired now. One position was with Baylor university maintaining the HVAC equipment on campus which involved 2000 ton chillers for cooling, absorption boilers and turbine generators fueled with reclaimed heat from the boilers, not exactly a job for an amateur.

The box dropping the line set through the roof would of course be properly flashed and sealed by a professional roofer I hope so no worry about leaking and is common, and no different then a vent pipe or flue exhaust. There are only a handful of people on houzz who knows anything about HVAC with practical experience, Elmer isn't one of them.

Kevin not to demote you or anything, but maintaining big equipment such as chillers is primarily going around with a grease gun belts and filters, checking things on a daily basis with the rest of the time sitting around waiting for something to break. It doesn't mean the job isn't important but 360 degrees different from residential retro fit or even new construction for that matter.

Commercial HVAC is completely different animal for the primary fact that nearly all commercial businesses are leased... and most of these types of jobs on the side of Commercial HVAC is maintenance related. (filter, belt monkey kind of job)

I know because I used to do this job over 20 years ago and left it mostly due to sheer boredom, among other issues with the way my HVAC career was headed if I had stayed in that role. (punching a clock for someone else to tell me what to do.)

That said: you have to know a good deal to work on chillers. Just as much you have to know plenty to work on residential... it's different.

You wouldn't hire a botanist to perform brain surgery? Well you can, but the outcome would look like what? People love to play specialist on this board.... because they do the one thing they hate others do to them demote them.

What is experience? Most of it is actually doing it. Which is completely different from maintaining it.

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On the side of offering my opinion on this topic: There isn't enough info to do so realistically. HVAC is an on site job 9 times out of 10.

Not in this business to guess.

That is the difference from a pro who actually does the work you want done.

When the day comes for me to retire, I seriously doubt I will offer an opinion any longer.

WHY: because my opinion is worth something. My time is worth more.

So why post here on this topic: to offer perspective. Take it or leave it. You make a mistake, you spend more money to fix it later, or you sell it to the ugly home people for pennies on the dollar. No biggie it happens all the time in residential RE.

Commercial RE? nope. They're leased, the lease doesn't typically include HVAC or anything else. It's typically a shell for the lessor to do as they want on their own dime. Back when I worked Commercial belt, grease monkey job... my employer dumped at least 10 million dollars on a building lease new location for an off shoot. That was back in the mid 90's.

It wasn't my job to do any of that, my job was to maintain and check it. Very different from what I do now as a Texas licensed HVAC contractor.

I service the Katy, Texas area.

"@Elmer J Fudd,

Understand what you are saying, but we already have roof penetrations elsewhere and we do not want soffits inside. We don't get much rain in SoCal."

Yes I know. I wasn't at all offended by this comment but I am a SoCal native myself, something you had no likelihood of knowing. I moved to the Bay Area for employment reasons several decades ago but I have a second home in coastal SoCal. Which is where I am right now, The weather has been beautiful as it usually is while rainy at home last week .

Good luck. In your shoes, I still would not add any avoidable holes into a flattish roof. An advantage of a soffit is that that puts the equipment "within the envelope", as the pros like to say. The mild weather of SoCal won't make that such a huge advantage, but remember that the gotal of HVAC equipment is for efficiency and performance, not appearance.

I'm glad you receive satisfaction from what you do ray, but to be frank you do not impress me, and to be fair I am nothing to be impressed by either.

Your opinion is worthless, there are 7 billion in the world to choose from so back off on the all mighty Ray rants on how valuable your opinion and time is.

Sure my opinion is based on experience. 26 years. Those 26 years are different from yours. Not here to impress anyone. It is what it is... what is a mistake worth? Had I accepted taking a paycheck in exchange for someone else telling me what to do.

No Regerts: The tattoo artist who didn't know how to spell. Mistakes. That is why you listen to a pro who actually does the job you are wanting done.

I run a HVAC business. That is the only reason I am here. I have no axe to grind... I am not a lumber jack.

Truth: You know it's the truth because it doesn't offer you any favors and most of the time it's ugly.

Candy coating: no one can stand the thought of telling you like it is, so they cover it up with sugar. It's pleasing to the ears everything that you want to hear and more and it tastes good too.

The question is which opinion is going to steer you the right way? right meaning the opposite of wrong.

I can't stand to use someone who thinks they know it all? I am in a thread in which work that is being done is work that I perform. I am not in a thread discussing the mechanics of chillers or alternative energy.

The alternative is to use someone that has an opinion but nothing more. To you I say: go for it.

Commercial roofer here. Last thing I'd do is run the lines in the deck flutes. If you ever have a new recover roof installed I guarantee you'd end up with a screw through your lines.

This is equaql to the same reason electrical and plumbing isn't allowed to be installed above or immediately below the roof deck anymore.

Alot has changed since this post aired 3 years ago. But my opinion is still worthless and I'm still in the HVAC business. Who would have thunk it at the time.

And you Kevin9408? how has the last 3 years treated you?

Any resolutions for 2025?

I have a similar requirement to run line set of 35 feet on roof - which is shingles. This is DIY project to install mini split. Attic run is possible but will have 6 turns. What Insulation do i need, Also fastening to the shingles - any ideas

.Location southern California - we get 110 F for couple of weeks