I am converting oit to gas and I got a proposal with Navien boiler. Has anyone heard of this brand? I heard it's fairly new and can't find information about it. Also, if I were to choose a more established brand should i go with Burnham Alpine or Weil Mclain? Any pointers will be greatly appreciated.

If you have proposal for CH240, then it is only boiler made by Navien legal for nyc installation to the best of my knowledge  It is made in S Korea, cheap and used by low grade contractors who compete on price for builder grade jobs or low grade installations. Quality control was poor and probably got better now. In short it is Kia of the boilers. Other models are not suitable for NYC installation because there is no H stamping.
  Burnham Alpine is a good boiler but they are using outdated Gianoni heat exchanger, Most manufacturers are moving away from Gianoni heat exchangers today. Weil Mclain is a good brand, they have models with different heat exchangers,  most known is Ultra line of boilers, they have aluminum Heat exchanger and sensitive to PH of the water, stay away from GV90+, This is boiler lacking necessary controls like outdoor reset and firing rate modulation.
  As a general note, no matter what brand you pick, sizing of high efficiency boiler is crucial for your project. Over-sizing of the boiler as usually done in this trade is not acceptable and will lead to non efficient performance and premature failure. I see you are looking for combi boiler. Be careful, heating load might be very different from DHW load. Often combi boilers are the worst possible solution. System must be chemically cleaned and water must be treated with water conditioner. Acid neutralizer MUST be installed.
  Any of these better than Navien in my opinion. keep in mind Burnham and Weil Mclain do not make combi boiler as i can recall. you will need indirect fired water heater.
  ANY high efficiency boiler must have parameters set up during start up. You must insist on installer doing proper parameters set up and not leaving factory defaults.
.You can take a look at Triangle Tube combi boiler line or Viessmann combi as well. Slant Fin makes decent combi boilers. Ask installer provide 3 references on high efficiency boiler installations during last 3 years. talk to clients, ask about warranty support from installer. ask about savings resulting from installation. Ask about repair history. general experience with installer. Not every plumber can do proper boiler installation. And between those who can, few know high efficiency boilers

Viessmann Vitodens 100 WB1B boiler and Vitocell 300 indirect fired water heater installation in Brooklyn

What sets this installation apart from the rest is application of variable speed drive deltaT circulator on boiler circuit.We are now capable to control water flow trough the boiler with set temperature difference  between water inlet temperature and water outlet temperature of the boiler.

My apartment is 1000 SF can i install Baxi Luna Combi boiler?

This is a question I get very often and installations I see all the time. While the Baxi Luna and other combi boilers are great systems and can work very well when installed in the proper application and way, they should not be installed in small apartments. The reason for this is that an apartment of that size has a very small heat load but a rather high requirement for domestic hot water. Minimum domestic hot water load even for smallest apartment is over 100,000 BTU per hour. Meanwhile heating load is minimal, somewhere in 10,000-15,000 BTU/HR on average winter day. Combi boilers are usually sized between 110,000-130,000 BTU per hr and minimum stable load for efficient operation of Baxi Luna combi boilers is 20-25% of rated output somewhere around 25,000 BTU per hr. So high efficiency condensing modulating Baxi Luna boiler turns to be short-cycling low efficiency boiler with shortened life span, complete lack of comfort and skyrocketing fuel bills when installed in small apartments.       
  So, does it mean small apartments cannot get modern efficient condensing modulating boilers installed? Of cause yes, it is possible. But it will require installation of, I would say, micro boilers, boilers with very small output, specifically designed for this application. Boilers with lowest output at 9,000 BTUHR,  and highest output at 40,000 BTUHR. These boilers require additional indirect fired water heater, working off boiler hot water, and will drive cost of installation way over the price regular apartment owner would budget in. BTW, these small output boilers cost more than their bigger brothers. Not near $8,000 incompetent fly by night operators charge unsuspected apartment owners. And this is another issue customers are facing: how much should we pay for new boiler? It depends. Answer one question: do I feel lucky? Do I want expert installation, legal and professional installation, or I want just someone who knows how to connect 2 pipes together. 

Boiler condensate was dripping

On copper pipe. And result was completely corroded copper. For some reason acid neutralizer is considered to be not very important element in condensing boiler installation. I think it is very important to install acid neutralizer.

By the way, owner of this boiler did not want to pay for correction of this installation and nothing was done to correct it.

How to have a boiler replaced (without getting steamed)

Another excellent article from heatinghelp.com

"We haven't had decent heat since that heating contractor left our basement," the woman complained. She was about as angry as any homeowner who had ever called me. "We paid good money for that new boiler," she continued, "but we still have uneven heat throughout the house, just like we did before. And it sounds like the hammers of hell are pounding on the pipes, just as they did before. What do you think we should do?"
I felt her frustration, but I have to admit, my first thought wasn't about what she should do. I was thinking about what she should have done. You see, the way I figure it, the best time to discuss heating problems is when you're contracting the job, not after the job is finished.
There's an easy way to avoid the most common heating problems. All it takes is a good checklist, some negotiating skills, and the willingness to shop for the best value rather than the lowest price.
Here's some advice I'd give my best friend if she were shopping for a boiler.


http://www.heatinghelp.com/article/236/For-Homeowners/1490/How-to-have-a-boiler-replaced-without-getting-steamed

Viessmann 200 WB2B boiler installation

Oil to gas conversion in Staten Island NY, Viessmann 200 WB2B  with Vitocell 300 indirect fired water heater, system pumping with Taco excellent Bumble Bee variable frequency drive delta T circulator, boiler side Grundfos circulators with B&G circuit setters balanced to 40F delta t across boiler heat exchanger. It is fan to see how boiler and pumps work together reacting to each other keeing perfect system balance.

Viessmann 200 WB2B boiler installation

  

Power flush

We always flush existing systems, then do chemical cleaning using Sentinel X400, and filtration, and after another flush we adding sentinel X100 for water conditioning. below is a picture taken during on of power flushes.

Power flush