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Old 11-08-13, 12:06 PM
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I'm in need of a new boiler. Everyone seems to think a mod/com is the way to go. Here is my current situation and current setup. I am using my existing boiler to heat my hot water needs to 125 degrees. The boiler is actually functioning correctly but is not suppose to be run at this temperature because of corrosion and carbon dioxide concerns. I really don't understand how a condensing boiler can work in my situation. If my needs (hot water for domestic water use and all heating requirement) only needs 125 degree water to keep us comfortable here, why would I want to heat the water in a mod/con to 160+ degrees then cool it down for my use, then heat or cool again to condense? Oh yea--my heating includes 700 sq ft of in-floor pex tubing covered with wood--this can only take up to 125 degree heat or it will delaminate. My wall hung radiators in three different rooms were oversized so a lower temperature water would be sufficient. these also work great using the 125 degree water temp. I also have an indirect water heater--also 125 degrees. What am I not seeing here and what kind of boiler system will work? Are there diagrams somewhere indicating fittings etc. to accomplish this goal I have? Thanks
 
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Old 11-08-13, 02:53 PM
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why would I want to heat the water in a mod/con to 160+ degrees
Mod cons are well suited to radiant heat.. They operate at lower temps then a standard boiler. The boiler you have now should not be operated below 140F... For your set up you would need a mixing valve to reduce the temps to the zones.

If you have your boiler set that low and its a standard boiler then it will get condensation and corrode...yes..

Mod cons can operated a low temps.. 80f and such and not corrod.
 
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Old 11-08-13, 03:15 PM
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totally confused

Lawrosa--thanks for your reply. Maybe i'm making things more complicated than they are. I can't find any information that sais the heat temp output of a condensing boiler. I did find a source that sais return water should be approx. 60 degrees. I would have to cool down the water two times--once so it's cool enough for my wood floor, then again before the water returns to the boiler because the water would still be to hot. This to me sounds inefficient. The 60 degree mark was in a write up explaining the delta T. With a higher temp than 60 degrees, efficiency is lower. This write up also sais that many peoples mod/con boilers are not reaching their efficiency ratings because of too hot return water temps. Does this sound correct? Also, do you have any idea where to find diagrams explaining the correct plumbing layout? Thanks for your help
 
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Old 11-08-13, 03:42 PM
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Where did you see this 'write up' ?

If we can read it also, we might be able to clear up some of your confusion.

The article might be F.O.S. too... after all, this IS the internet where any bozo can say whatever he wants and people believe him...

Like Frank Zappa was on Ted Mack Amateur Hour in 1951 (NOT true)... and I'm a French Model, bonjour........(ohhh, but this one IS true! ha ha ha ha )
 
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Old 11-08-13, 04:03 PM
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There is a write up by Jim Cook called Condensing Boiler Technology. There is a graph explaining output temp and return water temp and the degree swing or delta T and what these produce in boiler efficiency.
 
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Old 11-08-13, 04:24 PM
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Can you provide a link so we don't have to search?
 
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Old 11-08-13, 04:35 PM
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I found a very good PDF for you to read... Some may seem complicated but read it through and hopefully you will understand better...

http://fcxalaska.com/PDFs/CondensingBoilers_3.pdf

I believe what you read may be correct but you might be reading into it too much if the concept is not understood...

I like to edit dont pay attention to the end rebate info... and the eff claims although its possible...
 
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Old 11-08-13, 04:44 PM
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not sure if this link will work but try: http://www.fcxalaska.com/pdfs/ashrae...singtechnology.
 
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Old 11-08-13, 04:56 PM
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Yes... I did google and found the same article and I think I can see where bbb may be confused.

Let's start with just a bunch of statements that are true:

Your home has a certain amount of heat loss. The heat loss of your home increases as outdoor temperature decreases.

In order to maintain indoor temperature, you must have a means of replacing that lost heat.

In days of old, when men were bold, and heating systems were invented, these systems required high temperature water to emit the required BTU to keep the home at temperature.

The amount of heat emitters installed was based on what we call a DESIGN TEMPERATURE, which in fact only occurs for a few days each winter. At ALL OTHER TIMES, there is more heat emitter than needed.

MUCH of the heating season can be accomplished with lower temperature water.

Modulating/Condensing boilers were developed to take advantage of this fact. The controls in the boiler itself are what determines the water temperature required based on outdoor temperature sensors.

A "HEATING CURVE" is developed which the boiler will use to automatically adjust the temperature of the water that is sent out to heat the home. This heating curve is programmed into the boiler at time of installation.

In MOST CASES a REPLACEMENT CONDENSING BOILER will NOT be able to operate in the condensing mode for 100% of the winter because the heat EMITTERS are sized for higher temperature water.

They WILL operate in NON-condensing mode for some portion of the winter, but one will still save over the full course of the heating season because the majority of the time the boiler WILL be able to operate in the condensing mode.

In order for a condensing boiler to be able to operate in condensing mode 100% of a heating season, one would have to install MORE BASEBOARD, MORE RADIATORS, or otherwise design the system such that the home can be properly heated on the coldest days of the season with boiler water temperatures BELOW 130F. This is the ONLY WAY that a condensing boiler will be able to condense 100% of the heating season.

So, you see that there are 'compromises' that have to be made when retro-fitting a condensing boiler to a system that was designed for 180 water on the coldest days of the year.

Does this help explain? Questions?
 
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Old 11-08-13, 05:12 PM
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NJ trooper. Thanks for that. We did out heat loss on this house based on 180 degree heated water. Knowing that we wished to run cooler water (thus be more efficient) we double sized every wall radiator at that time. And this does work with the 125 degree water running thru the wall radiators now. Actually our radiators have thermostats installed on them and are turned to lowest setting for now. Being Colorado, the outside temps have been down in the 20's already this fall. So all that said, if we install a condenser that produces the 125 degrees we are using now (or maybe even lower) the boiler should condense and be more efficient for more days vs. a higher temp requirement. Is this what this means?
 
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Old 11-08-13, 05:16 PM
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So all that said, if we install a condenser that produces the 125 degrees we are using now (or maybe even lower) the boiler should condense and be more efficient for more days vs. a higher temp requirement. Is this what this means?
Yes, exactly and absolutely!

If you've OVER-radiated your home such that you can use 125 water on a DESIGN DAY, you have done the right thing if the intent was to go with a condensing boiler... good for you!

The boiler PROGRAMMING is what will control the water temperatures that it will target to heat your home.
 
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Old 11-08-13, 05:25 PM
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totally confused

So--a condensing boilers efficiency can be as low as 80% on warmer fall days and can be maybe in the 90% range at other times. So, everything kinda rounds itself out. There is another attachment that is confusing to me and not sure if it is needed or recommended. The outdoor reset controller. Do I want this thing messing with my boiler?
 
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Old 11-08-13, 05:50 PM
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So--a condensing boilers efficiency can be as low as 80% on warmer fall days and can be maybe in the 90% range at other times.
No, that's actually backwards. Efficiency is HIGHER during the warmer weather when COOLER water is needed to heat the home. Probably never as low as 80... maybe 85% or so, same as a conventional boiler if water hotter than 135 is needed during colder weather.

The outdoor reset controller. Do I want this thing messing with my boiler?
Condensing boiler should have that BUILT IN. The data from that is what tells the 'brain' to target lower water temperatures.

You haven't yet asked about "which boiler", but if you want my opinion, TRIANGLE TUBE !
 
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Old 11-08-13, 05:56 PM
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totally confused

I have read up on Triangle Tube boilers and have actually dismantled a Baxi boiler once but it was a combo model I believe. Not much to them for the price they get for them. Thanks for your input here. Sure i'll have lots of questions down the line. barry
 
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Old 11-09-13, 06:35 AM
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Not much to them for the price they get for them.
You're talking about the Baxi I think?

There is no comparison to the T T boilers... don't think they are 'all the same'!
 
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