# Combi boiler or Standard- That is the question..



## totalnewb (Aug 12, 2014)

As my name implies, I have no idea what I'm doing when it comes to boilers, but I am trying to rapidly learn before winter. I do realize that this is for professional plumbers only, but to be honest, the questions I need answered are likely not going to be answered correctly by the DIY community. Ask an amateur questions and you get an amateur answer. In light of this, please excuse my trespass and if you don't want to answer me, please reserve the right not to.

So the situation: My natural gas boiler started jackhammering and no matter how much I attempted to purge the system, it did not seem to make a difference. Called a boiler company and they concluded the jackets in the boiler were likely crusted over with lime causing the jackhammering.. I suppose this is possible, since the unit is a 1959 Bryant 100,000 btu boiler .

The expansion tank is an open style (water with air, no bladder) and hangs in the rafters.. It is about half full of air and water. System has a manual fill valve (scary but works and is running at 12 pounds when hot. No backflow or other current code parts, so all of this will have to be revamped.

The boiler guys wanted to install a Weil McLain unit of similar rating (80% efficiency) for around 5000.00 dollars. This includes revamping the expansion tank, adding an air scoop, probably doing some code things like an auto filler and anti backflow valve and such..

Problem is, I have about 1000.00 and can probably at best muster 2000 more by begging, borrowing etc.. So I am stuck doing it myself, if in fact this seems to be the issue.

Looking around I came across the Navien NCB combi boilers, and I like the idea of replacing my inefficient 40 gal water heater and ancient boiler with one of these. I can probably get one for about 2400 shipped online, and because it handles the pressure regulation on the boiler, I would only likely need the air scoop, expansion tank, condensate filter (I have cast drains) and backflow valve as well as the servicing valves for convenience.. I will likely get my water tested for minerals as well, and get the proper filters to handle those too. I plan to get an outdoor temperature sensor for the unit as well and just use a wireless remote.

OK so some more specs before the questions start...

House is about 2100 square feet and is a single zone with 1 inch pipes that split somewhere to 3/4 pipes and then come back to 1 inch piping.. Location is South Dakota which can get very crispy in the wintertime. Some years January never sees a day above 0 degrees F.

Plan is to cut out the old boiler and put in the new one, making a primary loop with close t connections all in 1 inch tubing so that the piping can mostly be reused including the pump if possible. Pump specs are unknown, and if this is considered cheaping out, I'm happy to replace it too..

I do have the feet of the radiators as well if this is helpful, but their manufacture is unknown.. 91.333- feet or 1096 inches total radiator length. BTU loss in the house is about 77,500 btu / h as calculated by Slant/Fin at 0 degrees and 180 temp (which, if I can, I'd like to run the boiler at 165 so I can get the benefit of condensing). As I have heard there are limitations to combi boilers flow-wise (4.5gpm on the primary loop), I am planning on going to the ncb-240, even though technically it is "too big" for my heat loss, since it is a modulating unit that varies between 18,000 btu and 120,000 btu. I'd rather have the margin and sacrifice the .3% efficiency over the NCB-210. I'll also get some margin on the hot water.

First, is this a doable project for a novice like me (I am proficcient in sweating, wiring, etc..) , or am I better off just going with a Weil Mcclain unit of around 100,000 btu and 80% and being done with it? The project has to be done by me- no money for the labor or markup on parts, and it will take a lot of time at 10-13 % increased efficiency to burn up the 2500-3000 dollars I save doing it myself over having someone else do it. Although I clearly respect the value of a professional doing the work, and that markup is essential for a plumber to survive, I simply cannot afford a professional to service this; it must be me that does it.

If I use the Navien, I plan to use CPVC for intake and exhaust to handle higher temps if I find that on the really cold days I have to resort to using 180 degree water temps. The exhaust will be routed directly out the basement wall instead of up the chimney like the current unit. If I use a conventional unit, it will go where the current one is and use the existing chimney. I plan to be well within code on the exhaust system, and will probably have a CO detector installed to be sure all is well..

If this is a doable project as I've laid it out and is appropriate, what have I missed? Quite frankly, where do I even begin? Will I likely get enough temp drop in the pipe for the unit to condense with the footage I have, and is the footage too much for one zone? Will the last rooms be too cold with this much pipe if it does get to enough delta-t that condensing occurs? Is it better if I split the zone into roughly 2 segments? I could do an upstairs and downstairs zone, (drop roof ceiling in basement) but I am running out of summertime quickly. As I have previously stated, I know nothing about boilers, so any helpful direction is appreciated but please be kind.. I'm a newb and I've tried my best to research before asking questions.

Thanks so much for your help!


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## plbgbiz (Aug 27, 2010)

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