What is the benefit of Condensing Gas Combination Boiler


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Old 06-18-15, 06:52 AM
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What is the benefit of Condensing Gas Combination Boiler

I have a Gas Boiler (AFUE at 85%) plus a separate water heater. Both are around 15 years old. My heat and gas guy recommends changing this to a Condensing Gas Combination Boiler. But the cost of the Condensing Gas Combination Boiler plus installing it will come to $14.6K even though the cost of tie Condensing Gas Combination Boiler itself, a NAVIEN NCB-240 which is AFUE 95%, is around $2K. He claims, and I take him at his word, that the installation costs will be very large. So my question is what is the benefit of a combined Condensing Gas Combination Boiler? Does the installation cost sound right ? Also should I consider just upgrading my separate Gas Boiler and water heater separately ? Perhaps I just leave it alone. AFUE of 85% does not sound so bad to me.
 
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Old 06-18-15, 06:57 AM
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Perhaps I just leave it alone.
Yes, that would likely be my suggestion.

What boiler make/model and water heater do you have now?

There's nothing wrong with them, right? If not, there is no point replacing them.

Yes, MAYBE the fuel costs will be less, but in ten years or so you'll be shopping for a new unit, and the annual maintenance cost will be MUCH higher than what you now have.

Wait till you NEED to change.
 
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Old 06-18-15, 07:41 AM
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My boiler is a Slant/Fin VHS-120 which seems to be AFUE 82.2% (Sorry I had a typo before.) Water heater I am not sure. I have to check. I do have a Therm-X-Trol ST-12 Expansion Tank so my water heater most likely is also from Therm-X-Trol
 
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Old 06-18-15, 07:45 AM
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Say both my boiler and water heater are too old. Should also just consider installing a separate boiler and water heater. Sure the AFUE will be less, say 90%. But I am fine with that. Any thoughts on if that should be cheaper than $14.6K which seems very high to me.
 
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Old 06-18-15, 08:15 AM
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Let's run some hypothetical numbers here. Your present Slant/Fin boiler is rated 66,000 Btu/hr net output, not huge. Let's assume that you are paying about $700 per year for natural gas. Let's be very optimistic, and assume that with that new boiler, you can reduce your annual fuel cost by $200, to $500 per year.

The payback period is $14,600 / $200 = 73 years. (That ignores the additional maintenance required for a condensing unit.)

With fuel savings of $200 per year, how much can you justify to pay for a new boiler? If you want to achieve a 5-year payback period, that is $200 x 5 = $1,000. If you would settle for a 10-year payback period, then you could justify paying $2,000.

Run your own numbers. But, it is almost axiomatic that replacing an existing boiler that is working satisfactorily can't be economically justified on the basis of fuel savings. It might be a different story if your existing boiler was completely shot, and you were debating on whether to spend a little extra to get an extra-efficient unit.
 
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Old 06-18-15, 09:22 AM
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$14.6K which seems very high to me.
That seems highway robbery high to me.

I'm not so sure I trust your guy.

That boiler could well run another 15-20 years with no problems...
 
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Old 06-18-15, 01:11 PM
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Say both my boiler and water heater are too old.
Your 15-year-old gas-fired boiler is not old at all. My hot-water boiler is 60+ years old, and runs just fine (with some replacement parts, such as the circulator pump, etc.).

The expected lifetime of a stand-alone gas-fired water heater depends upon the raw water quality and whether or not you routinely drain a bucket-full of water to remove sediment. But, 15 years is still reasonably young, in my book. The original water heater in our house was 50+ years old when I replaced it simply as a precaution.

How did you get the notion that your water heater and boiler are "too old"?

I do have a Therm-X-Trol ST-12 Expansion Tank, so my water heater most likely is also from Therm-X-Trol.
Is the expansion tank for the boiler or for the water heater? Either way, it is very common for the water heater to be a separate brand than the expansion tank. Therm-X-Trol expansion tanks are made by Amtrol - I don't think Amtrol makes direct-fired water heaters.
 
 

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