Boiler firing... Couple questions-


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Old 10-29-09, 11:47 AM
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Boiler firing... Couple questions-

Hey Gang,
I read a few threads about boiler firing times. There is a lot of info. I have a simple question that may end up as a long thread.

When my boiler fires, it seems to fire for quite some time. Maybe 30 minutes or more. Then it will stay off for quite awhile as well, maybe an hour or more.

The pipes and radiators are very cool when the boiler kicks in. The house is set at about 64 degrees all the time.

My question is this: Would it be better for the unit to fire for a shorter time, but more frequently?

I know that I need to get better info, which I will do tonight. But some basic info- The house is old, 1 story. The rads are old as well, maybe 80 or 90 yrs. The boiler is fairly new, but has a standing pilot and is naturally asperated.

Any thoughts?
 
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Old 10-29-09, 01:31 PM
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Is this a steam or hot water system?

How about the room temperatures? Is it comfortable or are there noticeable fluctuations and/or discomfort?

What make/model boiler? What kind of building?
 
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Old 10-29-09, 01:59 PM
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Hot water, not steam. The temp stays comforatable, no noticable differances in any rooms. It is a simple single story house with a full unfinished basement. The main floor seems well sealed with new windows and such. I don't know (yet), but I think I have at least some insulation in the walls. The attic (which is only accesable from an outside window) floor is well insulated. The house was built in 1919.

The boiler is a Burnham model 204NCL-TEI2
Standing pilot, intermitent circulation
Input- 96,000 btu/hr
DOE- 80,000 btu/hr
Water- 70,000 btu/hr
The energy tag on the side says it has a AFUE rating of 80.1
Max temp is 250, looks like the aquastat is set at 180.

I'm not really sure what all of that means... is the AFUE the same as saying "it is 80% effecent"?

Later in the evening I will time how long it fires for and then how long it is off for.

How long should the circ pump run?? I would think it should run til the water cools....
 
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Old 10-29-09, 04:21 PM
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How long should the circ pump run?? I would think it should run til the water cools....
Today 03:31 PM
The circ pump will/should run until the thermostat stops calling for heat... if you have a standard aquastat on the boiler.

It sounds to me as though you have cast iron standing radiators? and large piping, maybe 2" on the mains?

If so, your system has a large volume of water, and it may take a good half hour to heat it all up. Then, once it's hot, that cast iron just sits there and radiates heat into the home and delays the firing of the boiler for a long time.

The (sometimes) problem with this is that your boiler could be firing for a longer period of time while returning cooler water to the boiler... and there can be 'issues' with that.

Take a look at the piping around the boiler (or better yet, take pictures), and see if you can find a pipe with a valve on it that is running between the hot supply side and the cool return side. This might be a 'bypass' pipe that was installed to protect the boiler from the 'issues'.

If you can take pics, set up a free account at Image hosting, free photo sharing & video sharing at Photobucket and upload them there, and drop a link here for us to view the pics.
 
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Old 10-30-09, 04:55 AM
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Yes, it is about 1 1/2 or 2" pipe and old CI standing rads. I will look at the piping tonight. What issues are you speaking of? Problems with the cold water and the hot boiler tank? Like a hot coffee pot and cold rinse water?

Generally, what tells the boiler to fire up? The thermostat?

What does the aquastat control? Water temp, but does that mean that the boiler could shut off (the fire) and still circ hot water until the thermo is satisfied?

So, I should watch to see the when it shuts off / when it stops circulating??

What if it fires the whole time it is circ.... Wait, can it circ several times with one good firing, considering the large volume of water and CI rads?
 
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Old 10-30-09, 05:14 AM
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The boiler will fire until the water is up to temperature. If the thermostat doesn't call for heat for a long time then the water in the system will cool down quite a bit. Probably close to room temperature. So when you need the boiler to come back on again, it takes time to heat all that water again.

The exact same thing is happening in my house. My new boiler is much smaller than my old one so it takes longer to heat the water. With the outside temp being fairly warm, I don't need top the boiler to come on very often, but when it does, it takes time for the water to come up to temperature. I suspect that during the cold months this will become less of an issue when my thermostat calls for heat more often.
 
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Old 10-30-09, 04:40 PM
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Originally Posted by Milemaker13 View Post
What issues are you speaking of? Problems with the cold water and the hot boiler tank? Like a hot coffee pot and cold rinse water?
Yes, that's one of the issues, but not likely to be a big problem with your system because when the boiler fires up, it will likely be cool, so cool water coming back won't 'shock' it. If the boiler and system heat and cool together, no big deal.

The bigger issue would be if you have 'flue gas condensation' occuring. This happens when the boiler is firing, and the water coming back to the boiler from the system is below the 'dew point' of the flue gases. If this happens, the water vapor in the flue gases can condense on the cooler iron/steel surfaces on the FIRE SIDE of the boiler, and form a 'dew'. Because of the chemistry involved in burning hydrocarbons, several different acids can form. These acids can slowly 'eat' your boiler, flue pipe, and chimney from the inside out.

Systems with a large water volume such as yours are often plagued with this problem. Fortunately, there are piping strategies that alleviate the problem, the question is whether or not the installers used those strategies when they installed the new(er) boiler.

Generally, what tells the boiler to fire up? The thermostat?
I think it's safe to assume that there is only one 'zone' (one thermostat) in your home?

Yes, the thermostat will signal the aquastat control on the boiler that there is a heat demand. The circulator will run. If the boiler water is cool, the burner will also fire. If the water comes up to the HIGH limit setting on the boiler aquastat before the heat call is satisfied, the burner will shut off, but the circ will continue. If the call still continues long enough for the boiler water to cool below it's 'differential' (the spacing between burner on and off, usually 10-15) then the burner will fire again. This cycle will continue until the heat call is satisfied.

If the heat call satisfies before the boiler water reaches the high limit, both the burner and the circ will shut off.

What does the aquastat control? Water temp, but does that mean that the boiler could shut off (the fire) and still circ hot water until the thermo is satisfied?
Yes, see above.

So, I should watch to see the when it shuts off / when it stops circulating??
Sure, if ya gots nuttin better to do!

What if it fires the whole time it is circ.... Wait, can it circ several times with one good firing, considering the large volume of water and CI rads?
I guess it _could_... and some systems DO, but given the fact that most of your 'mass' is the water in the system, and the cast iron of the radiators, it's not likely. Chances are that the pattern you see now, is what you will see over the winter. As it gets colder outside, the time between cycles will get shorter, but once your t'stat is satisfied, it's likely that the boiler will shut down and cool somewhat before the next firing.

The scenario you mention is much more likely to occur with a large mass at the boiler, and smaller mass at the radiators... perhaps a big ole cast iron three times too large boiler feeding a system of fin-tube baseboards.
 
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Old 10-30-09, 04:56 PM
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Boiler manual

Do you have the manual for the boiler? If not, go here:

Series 2 boiler manual

and download.

Take a look at figure 3 on page 7. Proper 'boiler bypass' piping is shown. The text on that page explains the adjustment of the valves, and reiterates what I was explaining about the issues with flue gas condensation (FGC).

Hopefully the installers read the manual and didn't just use it as a kneepad to keep their chinos clean.
 
 

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