need lower boiler temp honeywell L8148e


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Old 11-02-09, 02:43 PM
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need lower boiler temp honeywell L8148e

I have a boiler with a honeywell L8148e aquastat. the tag that shows the other 4 digits is no longer on the case. This aquastat runs a circulator, the gas valve and a damper control. it operates in the 160-190 range. I need one that does the same but can go down to 120 and operate in the 115 or 120-135 range. This is because its heating a hydronic floor and heating an indoor endless pool and shares its boiler loop with a vacuum tube solar array which runs best in the 115-135 range. Any ideas what the last four digits of the aquastat i need are? my plumbing store says they can't even start on it unless they know the last four digits of the aquastat i have . thanks alot.
 
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Old 11-02-09, 04:22 PM
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You absolutely do NOT want to do that. Your flue gases will condense in the boiler and flue pipe. Flue gas condensate is very acidic. It will rot out your boiler, flue, and chimney in no time.

It's not as simple as just lowering the temp on the boiler. You need to PIPE for it. There are MIXING VALVES designed for the purpose.

If you are heating pool water, you need to use a HEAT EXCHANGER to keep the pool water separated from the boiler.

There's a lot to understand here, and mistakes at the front end will be very costly at the back end. Word to the wise!

"High on a mountain top, standing all alone, wondering where the years of my life have flown..."
 
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Old 11-02-09, 04:39 PM
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the system is already in place, including heat exchangers, etc. it works fine. at what temperature does the condensate occur? this is a very dry climate and we have only 7" of moisture a year. there is little if any humidity in the air.
 
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Old 11-02-09, 05:31 PM
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It has nothing to do with the humidity of the air.
[I probably shouldn't say _nothing_, as it probably does have some effect, but it won't be much]

When you burn hydrocarbons, the chemical reaction breaks down the fuel into it's components. One of those components is WATER. Some of the others are corrosive ACIDS. This flue gas mixture of superheated water vapor, and other nasty stuff has a very specific DEW POINT. If you are burning GAS the dew point of the flue gas mixture is around 135 F ... and if the surfaces on the interior of the FIRESIDE of the boiler are below that temperature, ACIDIC DEW will form that will eat your system.

I'm sorry that the system is already in place.
 

Last edited by NJT; 11-02-09 at 06:04 PM.
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Old 11-02-09, 05:41 PM
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not sure why you are so negative but thanks for the info. i would still like to reduce the boiler temp but maybe to 140 instead. just an fyi, i have mixing valves in place and the solar array can run much hotter but i harvest less heat. right now i have the solar running during the day and the boiler, if needed at night. like i said, it works fine and the boiler temp is 160 to 190 so there is no condensate at this point.
 
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Old 11-02-09, 06:06 PM
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How am I being negative?

I layed out the facts for you. It's physics. There is no emotion in physics.

If the fireside of your boiler is allowed to run cool enough to condense the water vapor out of the flue gases, your system will eat itself.

Also, it's the water RETURNING to the boiler that needs to be above the dew point of the flue gas. So, if your system is running a delta T of say 20, you should run the boiler at not less than 155 on the supply side.

Sorry about having to tell you this, and I'm sure it's not what you wanted to hear, but it's the way it is!

You CAN set your piping up with the proper design so that the system won't be damaged, but you can not run the boiler that cool...
 
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Old 11-02-09, 06:16 PM
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thanks, i appreciate the info. i had not thought about supply vs return. i guess i misinterpreted your remark "I'm sorry that the system is already in place. "
i guess i'll leave well enough alone. like i said, it is working well now, it was just something i was thinking about. maybe its time to move onto another project to distract myself from tinkering...
 
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Old 11-03-09, 05:35 AM
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Humidity does play a small role in the condensate but bear in mind that for every 100,000 btu's of natural gas burned you create 1 gallon of water. That in non-condensing boilers that water must be kept in a steam state until it leaves the vent or chimney. If not the boiler condenses and as Trooper stated looks like swiss cheese in a short period of time.
 
 

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