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Old 11-29-2008, 10:13 AM   #1
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Two Thermostats in One Heat Zone. OK?


I have a single zone for upstairs and downstairs. The thermostat is on the first floor. The second floor often is colder overnight. I wanted to install a thermostat on the second floor to control the zone and leave the one on the first floor. This is a 2 system. In theory this should work. (splitting the zone is very expensive) I have a hydronic monoflow system.

Has anyone done this before?

Thanks,
Mike

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Last edited by fishmanflats; 11-29-2008 at 10:40 AM. Reason: updated the system description.
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Old 11-29-2008, 10:33 AM   #2
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Two Thermostats in One Heat Zone. OK?


If you have one furnace for the 2 floors you would need a zoning system with dampers in the ducts in order to use 2 thermostats. One furnace cannot use 2 thermostats properly as it changes the electrical load on the circuit board etc etc. Impossible if you have A/C as one could call for cooling at the same time as one calls for heating (accidentally).

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Old 11-29-2008, 11:11 AM   #3
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Two Thermostats in One Heat Zone. OK?


Sorry, this is heat-only baseboard HW system. No AC.
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Old 11-29-2008, 11:15 AM   #4
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Two Thermostats in One Heat Zone. OK?


Hydronic heating systems utilize circulating pumps for the heating cycles.

A 2nd thermostat on the upstairs zone pump makes perfect sense to me.

You may need an additional pump control relay box to make the setup work properly.

This is practical if you have 2 pumps in the first place.
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Old 11-29-2008, 11:19 AM   #5
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Two Thermostats in One Heat Zone. OK?


You're going to wire this so that either thermostat will trigger the boiler?
That means that downstairs will get warmer at night than the downstairs tstat is set.
I don't see why that wouldn't work. Just wire the two tstats in parallel configuration.
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Last edited by Clutchcargo; 11-29-2008 at 11:21 AM.
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Old 11-29-2008, 11:29 AM   #6
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Two Thermostats in One Heat Zone. OK?


In many cases, the thermostat does not trigger the boiler. The aquastat does that function. The thermostat triggers the circulators.

Wiring them in parallel would defeat the purpose of installing separate zones/circulator pumps.
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Old 11-29-2008, 11:49 AM   #7
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Two Thermostats in One Heat Zone. OK?


Quote:
Originally Posted by kbsparky View Post
In many cases, the thermostat does not trigger the boiler. The aquastat does that function. The thermostat triggers the circulators.

Wiring them in parallel would defeat the purpose of installing separate zones/circulator pumps.
My boiler only comes on when the t-stat calls for heat otherwise it goes cold. I'm sure someone will correct me if I'm wrong but the only time that you need to maintain boiler temp is when there is a domestic HW loop going to it.
I thought the OP wasn't interested in adding a zone just a separate t-stat to control the upstairs. Whichever t-stat is colder would be the one that fires the boiler. His t-stat configuration would mean that the downstairs would get warmer than the downstairs t-stat is set for at night. It sounds like whoever installed the baseboard didn't do the heat loss for each room correctly or he's getting solar gain and needs to add insulation.
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Last edited by Clutchcargo; 11-29-2008 at 12:19 PM.
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Old 11-29-2008, 03:56 PM   #8
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Two Thermostats in One Heat Zone. OK?


I can turn down the valves on the radiators on the first floor. I have been slowly trying to determine the right valve settings, but it seems very dependent on the outside temperature. I also believe one room's radiator is sized too small.

Thanks for your replies. I believe that I will install the second thermostat. If I use an electronic one on a timer, I should be able to get enough comfort for the winter.

-Mike
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Old 11-29-2008, 11:36 PM   #9
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Two Thermostats in One Heat Zone. OK?


If you have a monoflo system.
DO NOT turn down any rad valves.
That will slow the water flow to all rads.

How high are the second floor rads above the boiler.
What is the boilers water pressure.
Has the circ been changed out in the last several years.
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Old 11-30-2008, 06:33 AM   #10
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Two Thermostats in One Heat Zone. OK?


Quote:
Originally Posted by kbsparky View Post
In many cases, the thermostat does not trigger the boiler. The aquastat does that function. The thermostat triggers the circulators.

Wiring them in parallel would defeat the purpose of installing separate zones/circulator pumps.

if wired properly a call for heat should always fire the boiler along with the circ (unless its at the high limit setting)

Last edited by Mainah; 11-30-2008 at 06:36 AM.
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Old 11-30-2008, 09:20 AM   #11
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Two Thermostats in One Heat Zone. OK?


Quote:
Originally Posted by beenthere View Post
If you have a monoflo system.
DO NOT turn down any rad valves.
That will slow the water flow to all rads.

How high are the second floor rads above the boiler.
The boiler is in the basement, so I would say about 20 feet.
Quote:
Originally Posted by beenthere View Post
What is the boilers water pressure.
I turned on the boiler and let it run for a few minutes: pressure seems about 15-20 psi.
Quote:
Originally Posted by beenthere View Post
Has the circ been changed out in the last several years.
No. I have lived in the house about 8 years and never changed. The circ is a bell and gosset series 100 (h68). There are 8 radiators connected, 4 upstairs and 4 downstairs.

The ironic part is that the radiators in two of the three rooms delivers too much heat, overheating the rooms. I turned those down to compensate, but overnight the temp is usually 4-5 degrees F cooler upstairs than downstairs. The last room upstairs, the valve is fully open. This radiator is the first off the boiler. This is the coolest temp-wise upstairs, maybe the rad is too small. It has side attics on two sides. I have insulated the walls, joist below and ceilings as best as possible.

I thought having the second thermostat might help regulate this issue.

Thanks
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Old 11-30-2008, 09:32 AM   #12
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Two Thermostats in One Heat Zone. OK?


Second stat will do as others said, cause the first floor to over heat while making the second floor warmer.

The rad you said is first off the boiler. Is it the hottest rad?
If not, its actually the last off the boiler, but looks to be first because of the piping.

The B&G 100 series, is not always the best circ for monflo's.
I've seen more then one place that a tech didn't use the right bearing assmbly when replacing one, on a monoflo.
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Old 11-30-2008, 10:44 AM   #13
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Two Thermostats in One Heat Zone. OK?


I believe it's the first. It is the first to get heat, I am not sure about being the hottest, but it is the smallest of the bedroom rads, about 1/2 size of the other bedrooms.

I have thought about using TRVs and perhaps putting a larger rad in the small room.

Thanks for your input.
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Old 11-30-2008, 10:51 AM   #14
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Two Thermostats in One Heat Zone. OK?


Monoflo systems are very flow rate specific.
Too little can cause what your experiencing. Because the mono tee isn't restrictive enough.

Do a temp rise on your boiler, post it, and what size boiler(BTU) you have.

Another thing you can do. Is put a top on the rads that are in rooms that get too warm. This will reduce the amount of convection you get from them.
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Old 11-30-2008, 12:05 PM   #15
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Two Thermostats in One Heat Zone. OK?


Here is a suggestion!! You could be able to separate the two floors to make two zones from the basement below. that would be the best bet! with a monoflow system, there's usually is a 1" loop with two tee's cut into it. then 1/2" coming from the tee to the rad.. find the monoflow tee that brings the hot water to the second floor and remove it and install a standard coupling on the feed side and the same for the return side. then run a new loop for your zone to the four pipes leading upstairs.don't forget to install the monoflow tee's.
And also check and see if the system was repaired at some point. I have seen Mono flow tee's installed backwards which will make the system not work properly. there should be and arrow on the tee to show the direction of the water flow. BOB.

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