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Old 08-22-2011, 12:58 PM   #1
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condensing boiler decisions


I'm thinking of replacing my current old boiler 78% efficiency with a new 95% efficiency boiler.
I learned from researching that in order for the new boilers to even get this high efficiency you need the return water to be 122F or lower according to manufacturers specs.
I have baseboard radiant heat which returns the water usually at 180F but after further research I learned that you can dump the return flow into a storage tank where it will cool the water and heat for your existing hot water tank's intake inlet.

I have a amtrol boiler mate which is 40 Gallon tank connected to the current boiler.

Is there a way to pipe this system so that I can still use the return flow of the system into the amtrol tank inlet from the return radiant which would cool the water down?
Also I still need to use the amtrol on demand in the summer when I do not use any heat.

I was thinking of piping the amtrol on it's own zone but allowing the return loops of the radiant to heat the water in the tank as well which would also increase the efficiency of the boiler there by reducing the water temp before it got back to the boiler.

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Old 08-22-2011, 01:39 PM   #2
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I've also heard about primary and secondary loop designs to use instead of using the storage tank as a cooling method.

Anyone have more details?

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Old 08-22-2011, 08:16 PM   #3
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Using your indirect won't get you the efficiency, since it won't cool the water as low as you have been lead to believe.

You can still get high efficiency from a condensing boiler with your hot water baseboard. by using the right circulator to make sure you have the full 4 gallon per minute flow rate for the baseboard. You may have to use primary secondary piping to get the proper flow. And then use outdoor reset to control the water temp. The water doesn't need to be 180- when its 30 degrees outside.
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Old 08-22-2011, 08:29 PM   #4
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I found a nice boiler which has the secondary and primary loops built in and comes with an outdoor reset.


how does the circulator help in the process of condensing?
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Old 08-23-2011, 04:10 AM   #5
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The lower the water flow, the higher the water temp needs to be to get enough heat output from the baseboard.
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Old 08-23-2011, 07:43 AM   #6
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Do you have details on the proper flow rate Gallons per minute etc...?
I'd like to make sure my current taco circulators are sufficient.
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Old 08-23-2011, 09:03 AM   #7
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condensing boiler decisions


Pardon my ignorance...but why would cooling down water just to heat it back up again make a boiler more efficient?
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Old 08-23-2011, 09:23 AM   #8
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Originally Posted by secutanudu View Post
Pardon my ignorance...but why would cooling down water just to heat it back up again make a boiler more efficient?
One of the hot gases produced in the combustion process is water vapour (steam), which arises from burning the hydrogen content of the fuel. A condensing boiler extracts additional heat from the waste gases by condensing this water vapour to liquid water, thus recovering its latent heat. A typical increase of efficiency can be as much as 10-12%. The effectiveness of this condensing process varies, it depends upon the temperature of the water returning to the boiler, but for the same conditions, it is always at least as efficient as a non-condensing boiler.

http://en.wikipedia.org/wiki/Condensing_boiler
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Old 08-23-2011, 09:26 AM   #9
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I understand that the condensation releases heat, and the heat exchanger picks up that heat to gain efficiency. So it uses the cool return water as it's "cooling agent" to run the exhaust gas through?

I have a new triangle tube high efficiency boiler...my return water temp is usually not much less than the supply, but the condensation pump runs constantly.
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Old 08-23-2011, 10:42 AM   #10
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Quote:
Originally Posted by secutanudu View Post
I understand that the condensation releases heat, and the heat exchanger picks up that heat to gain efficiency. So it uses the cool return water as it's "cooling agent" to run the exhaust gas through?

I have a new triangle tube high efficiency boiler...my return water temp is usually not much less than the supply, but the condensation pump runs constantly.
Under what temp's outside does it condensate?
Have you actually measured efficiency with a meter?
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Old 08-23-2011, 10:46 AM   #11
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condensing boiler decisions


I haven't really looked at it that closely (or used a meter)...so I'm not too sure honestly.
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Old 08-23-2011, 12:06 PM   #12
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spoke with the manufacture and the condensing boiler I am going to buy Utica SSC Boiler has a circulator and primary and secondary loop built in it to cool the temperature down to cause condensing.

I guess I'm good to go and shouldn't need to worry about the water temp's.
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Old 08-23-2011, 04:28 PM   #13
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Quote:
Originally Posted by aot2002 View Post
Do you have details on the proper flow rate Gallons per minute etc...?
I'd like to make sure my current taco circulators are sufficient.
through your baseboard, 4 GPM.
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Old 08-23-2011, 04:29 PM   #14
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Quote:
Originally Posted by aot2002 View Post
spoke with the manufacture and the condensing boiler I am going to buy Utica SSC Boiler has a circulator and primary and secondary loop built in it to cool the temperature down to cause condensing.

I guess I'm good to go and shouldn't need to worry about the water temp's.
They gave you sales hype. other boilers have the primary secondary piping built in them also. The water is not cooled down by it.
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Old 08-23-2011, 04:34 PM   #15
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What then is the purpose of the primary and secondary loop?

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