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"Great customer service. Very nice people. 
Honest opinions.  We will definitely have them come back out to install our HVAC system, we just have some other house projects we need to have done prior to the A/C unit being put in. "

"Keith came over for an estimate the previous Friday, took one look at our old tank water heater, and let us know what a liability it was.  We were then persuaded to go with a tankless water heater -- I have to say that I wasn't hot on the idea initially due to cost recovery being nearly impossible on them due to high installation costs having to rejigger the plumbing, add electrical, and update the venting.  However, we had decades of code violations which would have added up to a monstrous cost (especially for the vent) to replace with a normal water heater.  The NPE-240A that we were persuaded to purchase uses PVC venting, which is routable through older metal vents -- thus is a cost reduction over installation of new, up-to-code metal venting.
Note that Gallagher will have a promotional first-visit price.  If you don't sign the dotted line to purchase a major service from them on that first visit, the price may increase by several hundred dollars on the next visit.  That is a little bit of a pressure tactic and we would have done a bit more homework had we known of it.  However, in this case, we had a potentially disastrous situation on our hands with that 23 year old water heater and didn't much feel like tempting fate by checking with other contractors for their costs and quality of service.
 After Keith left, I began to do some additional research.  I came to find that flush valves are a huge convenience with tankless water heater.  They allow you to easily isolate the house plumbing from the tankless water heater, connect two hoses to the heater and a pump, and circulate a lime scale dissolving solution (such as house-hold vinegar) to remove the scale from the heater exchanger.  I was worried that the install wouldn't come with these flush valves.  I called Gallagher at 9am on a Saturday morning and asked if they would be installing flush valves.  The initial answer from the on-call plumber was no.  Fortunately, Keith provided his personal/work cell phone.  I called to verify the no answer.  He assured me that the flush valves would be installed (and yes, they were -- and high quality valves too; single ball-valve, cast in Italy!).  Thanks, Keith, for taking my call on your off day.  That saved everyone a lot of grief :-)  So my nerves were soothed and I waited patiently for Monday to get that old, possibly leaking, tank water heater out of my house.
 On Monday, two technicians came out on time (Travis and Chad).  I don't recall which one was the experienced plumber, but one of them was definitely new and needed the experience (we all start from somewhere).  Both set out to do their work and were fairly efficient.
Only one mistake of note was caught.  The lesser experienced technician did accidentally cut a hole through my gas furnace vent cap, believing it to be the water heater vent cap.  The mistake was caught, and some sheet metal was cut and the cap was repaired with some mastic and water repellant stuff.  I don't know if that's code but I suppose I'll find out when the code inspector visits to close the permit... certainly the last thing I need is CO entering the house because the cap was reinstall or repaired incorrectly.
The copper pipes were completely reconfigured, and even shortened (which is always good for water pressure and heat retention).  The PVC outlet vent was installed through the old vent and spray painted black.  It can hardly be seen from the highway.  The experienced plumber ensured that the system worked well at full firing.  He didn't have a Manometer that worked with the unit, so we didn't get our gas pressure tested.  He said that the inspector should be able to do that; should I have made him come back to test the pressure?  Well, it seems to work with the gas stove going, but I haven't had a chance or a cool day to test the furnace plus the water heater and the oven.  Backing up a bit, they did install an outlet into the water heater closet, tying into the bathroom electrical on the other side.
The final result looked nice; the valves were mostly positioned in an accessible way.  The hot water flush valve is a little hard to access with the gas trap in front of it.  But everything got insulated, and a bit of PEX tubing was installed for the condensation line.  That was also insulated, so UV degrading the PEX shouldn't be a problem?   The heater was installed in an exterior water heating closet with a vented outside door.  The condensation line was linked up with the A/C condensation line.  The A/C condensation seems to still make it out.  Bonus that the PVC was extended off my patio, but the condensation does now exit just behind the A/C unit. I've read that the Navien produces somewhat acidic condensation so I'm only slightly concerned that large amounts of condensation could cumulatively affect the A/C metal footings.  We'll see what the inspector says (I'll update this review after that is completed).
Overall, the experience was nice, and we were not bothered too much with the Gallagher membership plan like last time.  The techs were personable and willing to explain what they were doing.  They even let me see what a bad idea it is to have galvanized piping interact with copper piping.  Yuck!  It is nice to get rid of all those corroded galvanized stub outs between the old tank water heater and the main service to the house.  They didn't mind that I was looking over their shoulders the entire time; personally, I hate when others do that to me, so good on them.  The experienced plumber graciously repaired some of the busted out dry wall with some of my left over dry wall, which was great, and helped complete one of my DIY items.  Only other thing that comes to mind is, ensure that the techs clean the cold water inlet filter after testing the tankless water heater.  I had to do that myself (per the install instructions that came with the unit) and it had some debris from the performed work.  The tech did explain how to clean that out as it is regular maintenance for tankless water heaters.  He also let us know that there is an inlet air filter that is easily cleaned.
Good experience overall; a few minor (?) issues cropped up.  I'll update this review when the inspector checks on the work.   The heater works great, even without a recirculation line.  I'm much happier to be serviced by a tankless water heater!

** Update post-Inspections **

After waiting a few weeks, and inquiring Gallaghers about the permit, and then receiving it shortly after that inquiry, we had the City inspector over.  He found that the tankless water heater did not have a properly sized gas input.  He caught the fact that the gas line reduced down to 1/2" somewhere after the house furnace.  For some reason the old water heater and adjacent stove had 3/4" pipe connected to that 1/2" pipe.  The installers did not notice this as a potential problem.  The inspector was concerned that if the house furnace were going, there wouldn't be much left over for the house tankless water heater.  Thus he wrote up the install as needing 3/4" pipe all the way to the water heater.  He also detected a hint of natural gas smell in the water heater closet.  We pointed out that the house furnace roof jack had been damaged and repaired.  The inspector took a look and wasn't so sure that the mastic would hold up to the vent's output heat.  So the jack/bonnet would have to be replaced.

It took one night to get a plumber out to fix the gas leak.  It took 3.5 weeks to get plumbers out here to fix the inspector's red tag items for upsizing the gas line and replacing the vent bonnet.  We had called Gallaghers many times during those weeks and were told they would get the installers in touch with us to schedule repa"

"Mega Power Electric is an excellent company to work with. Gary and his team are knowledgeable, honest, and will go out of their way to get the job done right. We installed panels and solar battery storage unit in our home and we're reaping the benefits of being clean and green."

"After having countless issues with our A/C and heating unit, John fixed it during his first visit to our home and we have yet to experience anymore issues with our A/C and heating. Thank you for your service!"

"Ezra at Landmark construction energy crew is a perfect company in my book! I honestly recommend Ezra and his team of plumbers, because he his honesty and integrity, qualities that are sadly hard to find these days! Ezra was extremely helpful and knowledgeable about the tankless water heater system that we installed, and he was kind enough to come over and take a look at our new unit after it was installed and to check with us that the monthly bills came down as well. In addition to that, Ezra installed our new tankless water heater with the remote control that connects outside the tankless water heater. Because the remote control was not waterproof and if it will be installed inside the water heater, it would short circuit if it got wet enough. Thank you Ezra for going above and beyond for a "customer" who didn't even get to use you! Much appreciated. I will definitely be using Landmark construction energy crew to service my new tankless water heater when it needs it!"

"Jim did a great job. He quickly assessed the problem and then took our unit with him to work on it more. When he got back to us, the fix would have cost more than it was worth. He gave us options for a new or refurbished PC. We felt the refurbished was a good deal and chose that. He came back and set that up and we are very happy with it. He then took a look at my laptop and again took it along. He tuned it up and installed a speed upgrade we wanted. Of course, we paid extra for the new unit and upgrades, but we thought the price was very fair. Jim seemed very knowledgeable and responsive. We will definitely call him again if we need any computer services."

"While cleaning the gutters; he discovered that I had a drainage problem because the house builder did not install the gutters completely.  And, he noticed that the leaves from my neighbor's trees were clogging another section of the gutters.  He then cleaned the leaves from the gutters and solved a problem that I had with a foul odor coming through a downstairs's bathroom drain.
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"Josh is amazing!  He was very helpful and skillful.  We had many things that needed to be installed/repaired.  He completed everything that we asked in a professional manner.
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"The serviceman did a great job in installing the new burner. Did it with ease."

"Air Duct Solutions told me they were going to call back in a year to see if I need anything, but they never called back. I had my regular air conditioning guy out here and he said the UV was installed in there. Hopefully, it's doing what it's supposed to do. They have them in hospitals, so it ought to work for my air conditioning. He was personable and we had an interesting conversation together. They did pretty well. My air conditioning hasn't had any problems since then."