Tankless vs boiler

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Old 08-21-13, 10:32 AM
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Tankless vs boiler

It is time to replace by boiler (very old) and I have an electric WH that has a few more years on it, but I would prefer gas. My heating contractor is recommending I replace both with a combo unit Navien CH-240. Anyone have experience with how functional this kind of unit is?
 
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Old 08-21-13, 12:15 PM
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Such combi units are popular in Asia and parts of Europe, where compactness is desired, but they have gained a small market share in the U.S. Navien is made in South Korea. Like other combi units, the mechanical components are crammed into a cabinet, possibly wall hanging. For maintenance and repair, it would not lend itself to DIYers, which make up this forum.

I notice that is has a stainless steel heat exchanger which may be subject to stress corrosion cracking, depending upon the chloride content of your water. Cast iron is more prevalent among U.S. manufacturers.

Many of the components will be proprietary - and will require a service person trained in this particular brand, not just an all-purpose HVAC person or plumber. You will need to satisfy yourself that service will be readily available in your area for at least the next 20-30 years. Personally, I would want to visit several installations and talk to the homeowners about their experience. Being a pioneer carries with it a bit more risk.
 
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Old 08-21-13, 03:17 PM
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How Old Is It?

P.S. You say that your existing boiler is "very old." But is there any problem with it? If so, what are they? If you are motivated by the desire for higher fuel efficiency, it is virtually impossible to achieve a reasonable payback period from fuel savings when replacing a boiler that works.

You should ditch the electric water heater ASAP and replace it with a gas-fired water heater. The common 40-gal gas water heaters cost around $300+ at big-box stores, and can be installed as a DIY project if your are handy. It will likely last 10-20 years, depending on your water quality.

More on combi units: I think that their compactness appeals to Asia and other locations that have fewer single-family houses with basements and garages - compared to the U.S. They may be putting their hot-water boiler in what we might call a closet or utility room? I have traveled some in Asia and Europe, and space there seems to be much more at a premium than in North America.
 

Last edited by gilmorrie; 08-21-13 at 03:52 PM.
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Old 08-21-13, 08:33 PM
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Thanks for the responses, I am a retired builder, so no problem tinkering with plumbing (although I wasn't a plumber, or HVAC guy) no experience with boilers, always lived on the left coast. Then I bought a fixer with Radiant heat, and I love it. I replaced the circ pump this winter, because it made horrible noise. The house came with a 5 year old electric water heater, that I relocated when I replaced all the galvanized plumbing with Pex. The boiler is real old, maybe 40 years (not sure) it leaks and smells of gas all the time, even tho I have had it serviced, and have cleaned the burners my self. So rather than have it go out in the middle of winter, I want to replace it now. When the Heat guy came out to look at it he had the great idea of one unit to replace both, but his bid is 7500. I am thinking now I can order a new boiler (125,000 BTU) for under 2k and replace it myself. I am not cheap, but don't want to waste money, and/or fix some thing that aint broke. So trying to decide what makes sense? Put in an expensive combo unit, or just replace the Boiler, or replace both and keep 2 systems? Still mulling it, and would love any thoughts or feedback.
 
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Old 08-21-13, 09:32 PM
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(125,000 BTU) for under 2k and replace it myself.
Thats big enough for a 5000 sq ft home....

Did you do a heat loss calculation...?

Its bad practice to just replace with the same size boiler thats there... Plus radiant presents its own challenges.....You would have to explain whats there as radiant uses lower temps...140 f boiler water... How are you obtaining those temps now???

A regular boiler does not like low temps......

So you really need to give more info if anything.... You could have a lot of issues if the installer dont know what hes doing....
 
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Old 08-21-13, 10:02 PM
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What I have now is a Hydrotherm HC-125B tag says 125,000 BTU in, 100,000 BTU out, the dial was set at 140 all last winter and system worked fine.
Sorry, I said radiant in previous post, I have radiators in the lower floor, and baseboard upstairs, not radiant, my mistake. The house is 2700 square feet.
 
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Old 08-22-13, 12:18 AM
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Geez.. I have an old HC 85..... I am finding it hard to part with it... Although oversized its a work horse...

I too turned down the temp on mine since I am over radiated.... I used 140 - 150 f water.


So are the baseboards copper upstairs???? Or cast?


So if a mix you may have had temp issues and condensation problems??? Possibly the boiler could be gunked up... Could be cleaned possibly...But its up to you....
 
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Old 08-22-13, 12:45 AM
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My off-the-wall guesstimate is that your existing boiler is at least TWICE as large as necessary and possibly as much as three times what you need. Living in the land of Hydroelectric power you may have fairly reasonable electrical rates so that a conversion to a gas-fired water heater may be a longer than usual payback.

I don't know about their current record but when they were first introduced to North America the Navian had a terrible record for failures and lack of factory support. Their advertising was impressive but they failed to "follow through" on their promises.

I personally do not like using the space heating boiler to also heat the domestic water but that is probably my personal hangup.
 
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Old 08-22-13, 07:43 AM
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Baseboards are cast also, house was built in 1951. Maybe 75,000 BTU would be better size?
 
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Old 08-22-13, 08:01 AM
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Basic calculation says for a 2700 sq ft home your looking at 67k btu boiler... That does not replace a heat loss calc to make sure, although the rough calculation seems to work out pretty close...

The thing with cast is you need some type of boiler protection piping done at the boiler itself... If not you may have low return temps and condensation issues... So even a new boiler can be damaged in no time...

Read here for some learnin'....................

Bypass_Piping_Explaination
 

Last edited by lawrosa; 08-22-13 at 06:32 PM.
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Old 08-22-13, 04:06 PM
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What Stainless Steel Alloy?

Many boiler manufacturers, including Navien, tell you that their heat exchanger is stainless steel, or whatever material - but don't reveal the specific alloy. Years ago, for example, when I knew a little bit about stainless alloys, 316L was -regarded as having very good corrosion-resistant properties - particularly in the presence of acids and chlorides. In my experience many years earlier, the Navy would have opted for Inconel or Monel if there was any doubt (and if cost was no object, which it seldom was).

If they told us the specific alloy, it would be easy to do a search of its properties and compare them to other alloys. There are more stainless alloys than you can shake a stick at, with varying properties and costs.

Of course, corrosion resistance is one important property, but others include machinability, welding, thermal properties, etc.
 
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Old 09-02-13, 06:27 PM
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It's 436S
Ferritic, or nonhardenable stainless steels, are classified in the 400 series, usually with 10% to 20% chromium content, and are normally specified due to superior corrosion resistance and resistance to scaling at elevated temperatures. With inherent strength greater than carbon steels, ferritics provide an advantage in many applications where thinner materials and reduced weight are necessary, such as automotive emission control systems. They are nonhardenable by heat treating and are always magnetic. Commercially available AISI grades are Type 409, Aluminized 409, 410S, AK Steel 11 Cr-Cb, 430, 434, 436, 439, Aluminized 439, AK Steel 18 SR, 444 and AK Steel 18 Cr-Cb. Typical applications for ferritic stainless steels include petrochemical, automotive exhaust systems, heat exchangers, furnaces, appliances and food equipment to name a few.

436STM alloy is a single phase ferritic stainless steel in the same family of alloys as Type 409 and Type 439. The ATI 436S alloy typically contains 17.3% chromium and 1.2% molybdenum which provide improved general corrosion and pitting resistance compared to Type 409 (11% Cr), Type 430 (16% Cr) and Type 439 (18% Cr) ferritic alloys. The ATI 436STM alloy is less resistant to pitting and crevice corrosion than Type 444 alloy (18% Cr - 2% Mo). Like all ferritic stainless steels the ATI 436S alloy provides excellent resistance to stress corrosion cracking in the presence of chlorides. It is stabilized with titanium for resistance to intergranular corrosion. Formability and weldability of the ATI 436S alloy are very good in common with ATI 409TM and ATI 439TM alloys. These characteristics make the ATI 436STM alloy an excellent candidate for use in automotive exhaust systems as well as other applications where resistance to chlorides and mild corrosives, combined with fabricability, are needed.
 
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