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Where would you place the thermostat in a single zone, 3 story building. Tt's a multi-family residential, 3 units, one unit per floor. The boiler is a high-efficiency condensing boiler in the basement, with hot-water cast-iron rads in all units. I know the ideal is to have multi-zones, one per unit, but that isn't currently a possibility. So is it better to put the thermostat in the first floor, since heat rises, or in the top floor, since the top floor is farther away from the boiler?

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  • Do all the rooms have equal amounts of outside skin and insulation thickness? Are all the rooms south/west facing and have equal solar gain? These both make it very difficult to balance a building... – Harper - Reinstate Monica Oct 7 '20 at 19:25
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    I would not have a single zone 3 story building. 3 zones would be the minimum, one per floor. This is guaranteed to be uncomfortable anywhere other than where the thermostat is located... – Ecnerwal Oct 7 '20 at 19:35
  • Yeah -- since you have hydronics already, zoning this system should be fairly simple to pull off – ThreePhaseEel Oct 7 '20 at 23:45
  • @ThreePhaseEel diy.stackexchange.com/questions/76086/… Many townhouse style buildings have only two loops, and each loop is a ladder that hits all floors. Zoning this would require putting in bypass pipes, which is very hard. – gbronner Oct 8 '20 at 0:01
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This is a common problem in NYC. There's no perfect solution.

What I've done is put in an electronic thermostat with remote sensors on each floor.

Then, using the data I've collected, I tell the thermostat which devices to obey at each time interval.

In general, each floor is a degree or two off from the other ones, but the top floor can be much hotter/colder than the other ones, and, of course, you get tenants who leave windows open in winter...

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    Of course, they may leave the windows open in winter because they have no other control over the heat and it's too hot... – Ecnerwal Oct 7 '20 at 22:40
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Generally you want to locate the thermostat where the inhabitants spend the most time. For example the living room.

But it's always going to be a compromise when trying to use a single thermostat to control an entire structure.

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I lived in the third floor of a building set up like this.

If you are the landlord and paying for the heat, you want the thermostat in the top floor apartment, at a high-ish temperature (maybe 72*F) and let the tenants on the 1st and 2nd floors deal with it.

If you are a tenant, and the landlord is paying for the heat, you want the thermostat on the first floor set at the minimal that tenant can tolerate, and let the 2nd and 3rd floor tenants open windows if they need to.

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