Turning on a currently cold zone while the other is hot.

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Old 01-04-13, 07:31 AM
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Question Turning on a currently cold zone while the other is hot.

We have two zones, the house itself and the enclosed breezeway. I just realized that the breezeway has been turned off since we moved in (November). I turned on the second zone last night for about four seconds when I thought about all that cold water from the pipes rushing into the hot boiler and that made me think of hot glass cracking when you throw in an ice cube. So, I turned it back off right away.

I want to turn the breezeway on, but I am concerned that the cold water will cause problems in the already hot boiler. Am I just worrying too much? I read some stuff online about thermal shock, but they only seem to reference commercial boilers.

We have a Weil-McLain from about 1956.

What would be the right way to go about turning that cold zone back on? It dropped down to 44 degrees in the breezeway last night.

Thanks!
Craig
 
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Old 01-04-13, 08:15 AM
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Do you have a separate thermostat for the breezeway? If so, won't a similar situation exist whenever that zone calls for heat?

But, to be totally safe, you could cool the boiler down to room temp before opening the breezeway zone.

If the breezeway is unheated, is it likely the heating pipes are frozen? Watch for any leaks caused by the freezing.
 
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Old 01-04-13, 08:55 AM
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Welcome to the forum.
A couple questions for you.
What type of and size of pipe is in this breezeway?
What temperature does your boiler operate at?
Does your zones have seporate circulation pumps or one pump and control valves for the zones?


44'F (6.7'C) is still above freezing, Frozen pipes as a result of it being off is currently a non-issue.

If it's a pump per zone, and the valves for this zone are closed, open the valves a bit (1/8 to 1/4open). This will allow some cold water to mix in with the hot, but not in a huge hurry.
Leave it like that for a 30 minutes or so. After that, fully open the valves.

I don't see mixing ~6'C (or warmer) water with 77'C to 82'C water as being a huge shock, but if the piping is older, the thermal expansion could do a number on connections.
 
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Old 01-04-13, 09:17 AM
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gilmorrie and Mike,


Many thanks for the welcome.


>Do you have a separate thermostat for the breezeway?
Yes. We've had it set to 55, but we didn't realize the zone was actually turned off.


>If so, won't a similar situation exist whenever that zone calls for heat?
If in the future we have the house set to 66 and the breezeway set to 55, I imagine there will always be something somewhat similar, although this would be slightly more extreme since it has been off for so long and it's winter.


>But, to be totally safe, you could cool the boiler down to room temp before opening the breezeway zone.
Sounds like a reasonable approach.


>If the breezeway is unheated, is it likely the heating pipes are frozen? Watch for any leaks caused by the freezing.
As Mike mentioned, I am hoping at 44'F that isn't the case, but I will definitely keep both eyes out.


>What type of and size of pipe is in this breezeway?
Looks to me to be about a half inch and it's black. That's about the best I can do at this point. It exits the breezeway loop and joins after a couple of feet with the larger black pipe along with the main house loop.


>What temperature does your boiler operate at?
The only setting that I've seen thus far on the boiler looks to be set at 180, but the temperature gauge in the window on the front of the boiler (I have no idea how accurate it is) seems to vary from 120 to 160 or so whenever I happen to stare at it.


>Does your zones have seporate circulation pumps or one pump and control valves for the zones?
There are two pumps that go off to separate loops. They appear to be on their own circuits and thermostats. There are four switches. Zone 1 circulator, zone 1 thermostat, zone 2 circulator, zone 2 thermostat.


I like the idea of turning the valves partially open and letting that mix. Perhaps if I also did so while zone 1 happens to be cycling on, there will be some nice active mixing between the two. Sounds good.


I am thinking of also using a space heater to first bring the breezeway up to 60F for a few hours.


Craig
 
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Old 01-04-13, 09:31 AM
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>What type of and size of pipe is in this breezeway?
Looks to me to be about a half inch and it's black. That's about the best I can do at this point. It exits the breezeway loop and joins after a couple of feet with the larger black pipe along with the main house loop.
It sounds like the breezeway is only a short run that leaves the loop and returns, kind of like a sub loop?
Am I reading this correctly?
 
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Old 01-04-13, 09:35 AM
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I don't believe there should be any issue at all...

How many years has it been that way? And nothing has happened yet, right? And I'm sure the PO's didn't take any special steps ...

I don't think there's enough water in that loop to cause an issue.
 
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Old 01-04-13, 10:46 AM
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Mike,

I meant a couple of feet once it is back on the main house side of things. The breezeway itself is about 10 by 15 feet and the pipes go around the perimeter.

Trooper,

You're probably right. As for the PO's, my thought was they'd have had the sense to turn it all back on well before January.

Right now I have the door from the house into the breezeway open. I'll let that get to house temp and then I'll set the valve to a quarter or so, wait for the house zone to cycle up, and then turn on the breezeway. After a bit I'll open the valve up the rest of the way, set the thermostat, have a beer, and stop worrying so much.
 
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Old 01-04-13, 03:58 PM
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I'll have one or six with you!

Let us know if there are any problems, there won't be...
 
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Old 01-04-13, 07:59 PM
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Yep. No problems outside of a water leak (about ten drops a minute) by the pump that subsided after ten minutes and has not resumed. Breezeway is toasty.

Thanks again

Now, time to look into my 170 degree tap water.
 
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