On Sunday, April 8, 2018 at 10:56:21 AM UTC-4, Ed Pawlowski wrote:
On 4/7/2018 10:17 PM, J.Albert wrote:
On 4/7/18 12:45 PM, Ed Pawlowski wrote:

I mentioned that he has a boiler and it has a high limit switch that
turns off the burner, but there was no response.

OP here.
If there's a "high limit" switch, it hasn't activated.
(that would be on the aquastat, right?)

I don't really want the furnace cycling on/off repeatedly, just to
maintain a specific setting on the thermostat by (say) +/- 1 degree, or
even 2 degrees.

I don't mind a drop of 3-4 degrees (or even a bit more) between having
it run.

What's really so hard to understand about that?


What is hard to understand is what you don't want to cycle. Do you mean
the burner on and off? The thermostat does not control that. Yes, the
aquastat does.

The thermostat senses the need for heat. It turns on the circulator
pump so hot water moves through the radiators. When warm enough, it
stops the circulator as no more heat is needed.

Meantime, back on the boiler (not a furnace) the water temperature is
sensed by the aquatstat and it turns the burner on and off to maintain
the water in a given temperature range. High limit is usually about 190
degrees. You don't want to exceed that as the pump can cavitate.


You have to clarify what you want to get the best answer. Do you want
the burner to cycle less? Do you not care about burner cycling but just
want to limit the time period is runs in an hour?

Technical terms: Furnaces heat air. Boilers heat water. They have
different controls.

Since he won't explain why he wants the system to run only once every three
hours, maybe we should work the other way. Let's list reasons that one would
not want the system to cycle *excessively".

1 - Each time a motor starts, there is some additional energy usage
to get it going and some additional wear/stress.

2 - Each time the system starts/stops there will be some small amount
of energy wasted as losses, for example heat left in the pipes in the
loop inside walls, etc.

If a system was cycling on and off 10 times an hour, I can see the above
being factors that would be of concern. But not if it cycles on and
off two or three times, at that point the above issues become negligible.
The systems are designed for that kind of usage over their normal lifespan.
And with the latter cycle rate you can keep the temp of the house constant,
which I would think would be far preferable to wide swings.

He also didn't answer the question of how he was achieving this with his
old thermostat. Was he? I've never seen any residential type thermostat
that could do what he wants.