Best way to run two zone heating??

GRod

Hello,



Im about to take possession of a home that has two zone heating and cooling. The t-stats(one in the 1st floor and another in the second floor) have timers built in for a particualr day of the week. My main question is what is the best way to set the temps for both zones in the following conditions for efficiency purposes:

1. When we are not home. What to set both t-stats? Is it better to set them both at one temp or completely shutoff the upstairs one?

2. When we are home and we are only on the 1st floor.

3. When we are home and we are only on the 2nd floor.

4. Is it better to lower the heat at nigh time when we are asleep?



By the way, the boiler is a water based using natural gas and baseboard heating.



Thanks for your help.

Jean-David Beyer

Your questions are too complicated to answer with the information you provided.

Too much depends on just how your heating system is implemented.



For example, I have a house with two floors, and two zones: one upstairs and one downstairs. The boiler is a mod-con with outdoor reset. I run different supply temperatures to the two zones.



 Downstairs is heated by a radiant slab at grade with 1/2 inch copper tube embedded in it. I do not employ any setback at all there at night or any other time because it takes about 24 hours to recover from a setback. If I am to be away for over a week, I set back to 62 F, when I normally run it at 69F. My thermostat allows me to turn the heat back up 24 hours before I expect to return. That works out OK. But if I am away for a weekend or something, I just let it run.



Larger setbacks are even worse. When Sandy came by, I lost power for 6 1/2 days and my indoor temperature dropped to 58F. When power came back, the heat went back on, but after a day or two, I diddled the reset curve for the downstairs zone to run much hotter than usual be able to recover faster. I thought it might take a week to recover otherwise. When it started to get close to my desired temperature, I put the reset curve for downstairs back to where it normally should be.



Upstairs is heated by baseboard. I  do a 1F setback up there (I do not normally use the upstairs at night), and it takes two to four hours to recover from that, because the reset curve is so tight that the boiler supplies just enough heat to overcome the expected heat loss, and not nearly enough to recover from the setback. The controller in the boiler is set so if it has not recovered in two hours, it raises the supply temperature by 10F so as to recover more quickly, and if, after another two hours it has still not recovered, it raises the supply temperature another 10F, and so on. There is an upper limit of 135F for the baseboard supply. So it never gets hotter than that.



I suppose your system is different, so your answers will be different too.



Some people believe that setback does not save any money because it costs more energy to recover from the setback than it does to run at constant temperature. That makes no sense to me for hot water or hot air systems, where no phase change of the heating medium takes place. It may be true for steam systems. But for comfort, if you have a high thermal mass in the system, be it a boiler that holds lots of water, or a concrete radiant slab, you will suffer a considerable comfort penalty due to the long time required to effect a temperature change. Is this acceptable to you? It sure is not for me.

pipeking

very true!

i on the other hand have a ranch with 3 zones, 1 for the bedrooms,bath,kitchen, 2 for the livingroom,3 for the finished basement. i have a conventional c.i. oil fired boiler, with a tankless, and fin/tube baseboard thru out the house. the basement tstat is kept at 58*, and the actual temp is 61*. the bedroom tstat is kept at 65 during the day and 69 at night. now the living room is very large and has tons of windows and get sun till 2oclock, so during the day (even on the coldest of days) the tstat is off untill 3:30. from 3:30-12am its set to 69* and from 12-530am set to 60*, and from 530-7 set to 70*.  now if my whole house was at 60* and i turned up the tstat to 70*, the tstats would be satified in about 20min+/- 5.  but u see all these temps i use r from trial and error, and getting to know your house and your heating system. every house and every system is different, and poeple think if they just throw a bunch off money into a system that it will be the most efficient thing on the planet, and the truth is, that u need to take an active aproach on learning what your system can do and how it works in your enviroment, then dial it in.