Off Topic Messages

Thermostat span setting

Fri Jan 17, 2014 11:15 pm

My home has an HVAC unit, and the thermostat has a span setting of 1, 2, and 3 degrees. Does anyone know if one span is efficient than another with heating? At a span of 3, the unit will come on less often, but run longer that on a setting of 1. Will either make much difference in the bill, or is it basically a comfort issue?

Re: Thermostat span setting

Sun Jan 19, 2014 1:38 am

You might be better off asking the question on a specialist plumbing forum. I've had some excellent advice before now on electrical and plumbing forums, as you often find that they are inhabited by qualified professionals who are more than happy to show off their knowledge to the public. But on a purely practical level, I can't imagine why you might want to use anything other than a 1 degree setting. We have ours set on a half degree either side, and that works fine for us.

For example, if you wanted a comfortable room temperature of 18 degrees, then by setting a 3 degree span - Incidentally, does that mean 1.5 degrees either side? I assume it does - you're going to have to wait until the temperature falls to 16.5 before it comes back on again, and by then you might be getting uncomfortable. As I say, ours is set at half a degree each way, and in practice once the radiators go off the room temperature continues to rise another half degree as well.

I'm sure that there's some complicated formula for efficiency, but in practice I doubt very much whether the difference is worth worrying about. I'd be more bothered about having to put up with the extremes of temperature, personally. I'll be interested to know what you find out though.

Re: Thermostat span setting

Sun Jan 19, 2014 4:14 am

The Pirate wrote:You might be better off asking the question on a specialist plumbing forum. I've had some excellent advice before now on electrical and plumbing forums, as you often find that they are inhabited by qualified professionals who are more than happy to show off their knowledge to the public. But on a purely practical level, I can't imagine why you might want to use anything other than a 1 degree setting. We have ours set on a half degree either side, and that works fine for us.

For example, if you wanted a comfortable room temperature of 18 degrees, then by setting a 3 degree span - Incidentally, does that mean 1.5 degrees either side? I assume it does - you're going to have to wait until the temperature falls to 16.5 before it comes back on again, and by then you might be getting uncomfortable. As I say, ours is set at half a degree each way, and in practice once the radiators go off the room temperature continues to rise another half degree as well.

I'm sure that there's some complicated formula for efficiency, but in practice I doubt very much whether the difference is worth worrying about. I'd be more bothered about having to put up with the extremes of temperature, personally. I'll be interested to know what you find out though.


Thanks for the response. I did ask on a Do it Yourself forum, and didn't get a concrete answer. I'll try some others.

I will admit that the lowest span would be the most comfortable, but it cycles more often, and I assumed that might cause more wear-and-tear on the unit and be more costly, but the difference might not be much.