Boiler short cycling, Oversized?


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Old 02-18-15, 01:55 PM
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Boiler short cycling, Oversized?

3 Story home
Tstat on each floor
FL1 22.4 Linear Ft of baseboard copper with aluminum fin
FL2 25.66 Linear ft of cast iron baseboard
FL3 25.9 Linear ft of baseboard copper with aluminum fin.

3 zone valves one circulator pump

Weil Mcclain cga 5 SPDN

Input 140,000 BTU Natural Gas

When Floor 1 or 3 calls for heat, the boiler runs up to 180F and shuts off usually in under 5 minutes.

Boiler is doing lots of short runs

I could care less about having multiple zones for even heating. A temp difference on different floors wont bother me.

Would having one t-stat control all floors help this cycling issue?

My thought is disconnect power from FL2&3 zone valve and push the lever forward to open them up. Then when FL1 calls for heat, the whole house gets heat. Boiler runs longer because load is greater and I dont have to hear boiler constantly cycling.

Good or bad idea?
 
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Old 02-18-15, 02:10 PM
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Just a guess without knowing a whole lot more about your house but most likely your boiler is at least 50% oversize and it could be as much as 150% oversize.

Yes, disabling the zone valves to make a single large zone would help with the short cycling but comfort would definitely suffer. I doubt that you would save much, if any, fuel by such a move.
 
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Old 02-18-15, 02:12 PM
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Total of about 75 feet of baseboard at 550 BTUH per foot = 42K BTUH of heat EMITTER installed.

Boiler is about 100K BTUH oversized.

Would having one t-stat control all floors help this cycling issue?
More load on the boiler should mitigate the short cycling to a degree. You STILL have a boiler that is about 2.5 X oversized, no matter what you do.

It will still probably short cycle, not as bad as when only one zone calls for heat though.

Good or bad idea?
There's more to it than 'good or bad'.

With an open zone valve, not only will you get heat when the one zone calls, you will also get heat all the time... because with the zone valve open, you will have THERMOSIPHON flow through the open zones. You might find that the other floors get REALLY warm... and the warmer you keep the home, the more fuel you burn...
 
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Old 02-18-15, 02:26 PM
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So not really any great answers I guess.

I have some extra cast iron baseboard that I could add in the basement but considering its 2.5x too big I doubt it will do much. Maybe I add a heated driveway to melt this snow. I bought the house with this unit in it. I wish more people knew their trade.
 
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Old 02-18-15, 02:31 PM
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It has little to do with people "knowing their trade" and everything to do with the fact that boilers and furnaces in residential systems are routinely oversized by about 100%. It has ALWAYS been this way and it is only recently that builders have started to properly size these things. After all, the LAST thing a heating contractor wants to hear is that the system they installed can't maintain the desired level of heat.

When energy was cheap and houses had poor insulation and air sealing the oversized systems simply weren't noticed.
 
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Old 02-18-15, 02:33 PM
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Try a piggyback economizer like the Intellidyne HW+. It will increase cycle times by monitoring the load on the system and holding the burners off. Worked great on my system, I got much longer cycle times.
 
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Old 02-18-15, 02:51 PM
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Thanks Tom, I will look into that unit.

My Zone valves are Taco 571-2

To disable 2&3 from calling for heat, do I remove the white wire from terminal #3?


 
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Old 02-18-15, 03:13 PM
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Remove the wire from terminal ONE.

When the zone valves are set to manual, if a thermostat happens to call for heat, it will revert to automatic. So, you don't want the thermostat to call for heat.

Removing terminal one will achieve that.

Of course, tape it up so it can't short out against anything else.
 
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Old 02-18-15, 03:24 PM
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Not sure I followed you 100%.

1.Remove wire from terminal ONE on valves 2&3 /tape it up

2. Manually open valve

Should I turn off the tstats in the zones 2&3
 
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Old 02-18-15, 03:40 PM
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Should I turn off the tstats in the zones 2&3
You can if you want. Doesn't matter...

Terminal 1 is the wire from the thermostat that tells the valve to open.

Removing that wire disconnects the thermostat from the valve.
 
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Old 02-18-15, 04:30 PM
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When Floor 1 or 3 calls for heat, the boiler runs up to 180F and shuts off usually in under 5 minutes.

Boiler is doing lots of short runs



But is the boiler short cycling??? Many get this term wrong IMO.. A short cycle is when the t stat gets satisfied before the boiler reaches its operating temp... Hence it did not complete its cycle...

If the boiler makes 180 f then cools and refires to continue to try to satisfy the t stat then that is a cycle. There is nothing short about it.. You can reduce the amount of times it refires to satify the t stat by adding base board...

So what issues above are you having?

Also it has been 0F in NJ... Possibly you have drafts..

I for one have my boiler lowered to 160F.. During the 0F night in NJ, I had t stat on 72F but the home never reached past 70F.. How many times you think my boiler fired on and off?? A lot...LOL..

This was all through the night... Home stayed 70F and there was a constant call for heat..

Now I could have raised the temp to 180F at the boiler and I could have satified the T stat... But we were so comfy with constant heat output all night...

I am oversizedby 50K btu on the boiler... But I am also over radiated for my heat loss....27K btu heat loss with 45K btu of radiation....
 
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Old 02-18-15, 05:06 PM
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With Wire ONE disconnected on zones 2 and 3 both tstats off,
push lever forward on zone two, nothing happens
push lever forwad on zone three, circ pump turns on and boiler fires.

Unit is wired as follows
reds from tstat to side mounted xformer terminal A
whites from tstat go to #1 termnials on Zone valves

Zone Valves
Terminal #2 all come together and go to xformer Terminal B and to Boiler black wire labeled transformer B

Terminal #3 All come together and go to boiler other black wire that says "to 24v Thermostat."










Lawrosa, I cant say for sure if the tstat is satisfied before the boiler reaches 180. I can say for sure that it gets up to 180 very very quickly for zone one. I timed it at 90 seconds while I was just down there.
 
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Old 02-18-15, 05:17 PM
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I can say for sure that it gets up to 180 very very quickly for zone one. I timed it at 90 seconds while I was just down there.
90 sec from what temp??? Maybe you have other issues...

How do you heat your hot water???

What the psi reading on the boiler gauge read???
 
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Old 02-18-15, 05:20 PM
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I would not mess with things now... Put the zones back... Its going to be single didgits again in NJ... Now is not the time to experiment IMO...
 
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Old 02-18-15, 05:46 PM
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Dont know what the starting temp was
Separate gas hot water heater.
Boiler is at 17 PSI

Leaving the boiler alone for now

Should manually opening zone valve call for heat? and if yes, why only on zone 3 but not 2. Does not seem right.
 
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Old 02-18-15, 06:06 PM
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T,
If you removed the wire from terminal #1 on ZV then manually opening the valve should not operate boiler.
Terminals #1&2 onZV open valve when tstat calls for heat. When tstat calls #1&2 open ZV and make end switch #2&3 which starts the boiler or at least the pump depending on your control.
 
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Old 02-18-15, 06:12 PM
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Its going to be single digits again in NJ...
Here in the Midwest, at 7pm Wednesday, it's already below zero. I'm hoping all this will move east.
 
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Old 02-18-15, 06:25 PM
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G,
Thanks for the goods thoughts. We're not far from you believe me, it's no picnic.
 
 

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