Avoiding large fluctuations

[micky]

Avoiding large fluctuations in temperature can be more energy-efficient
than allowing the home to cool too much and then reheating it from
scratch.

This refers to homes in winter.

Discuss. Defend or deny.

https://www.google.com/search?client=firefox-b-1-d&q=avoiding+large+fluctuations+in+temperature+can+be+more+energy-efficient+than+allowing+the+home+to+cool+too+much+and+then+reheating+it+from+scratch.

[Ed P]

Post by micky
Avoiding large fluctuations in temperature can be more energy-efficient
than allowing the home to cool too much and then reheating it from
scratch.
This refers to homes in winter.
Discuss. Defend or deny.
https://www.google.com/search?client=firefox-b-1-d&q=avoiding+large+fluctuations+in+temperature+can+be+more+energy-efficient+than+allowing+the+home+to+cool+too+much+and+then+reheating+it+from+scratch.

This is true. I've seen some calculations on energy needed to maintain
for 8 hours vs to reheat a large differential.

Efficiency aside, both summer and winter I lower the temperature at bed
time for comfort.

Another mistake some people make is setting the thermostat to an extreme
number. If they want to go from 65 to 70, they set the thermostat to 80
thinking is will heat up faster. No matter the setting, the heat output
(or cooling) is determined by the capacity of the unit.

[Mark Lloyd]

On Wed, 1 Jan 2025 23:03:47 -0500, Ed P wrote:

[snip]

Post by Ed P
Another mistake some people make is setting the thermostat to an extreme
number. If they want to go from 65 to 70, they set the thermostat to 80
thinking is will heat up faster. No matter the setting, the heat output
(or cooling) is determined by the capacity of the unit.

I was surprised, but I found that a furnace DOES heat up faster when the
thermostat is set higher (at least in one particular case). It seems to be
because of something in the thermostat called the "heat anticipator" that
turns the furnace off sooner.

It was set at 70, but off and the temperature was down to around 50 when
turned on. The furnace ran awhile and turned off around 62. Consecutive
cycles would increase the temperature more.

[Ed P]

Post by Mark Lloyd
[snip]

Post by Ed P
Another mistake some people make is setting the thermostat to an extreme
number. If they want to go from 65 to 70, they set the thermostat to 80
thinking is will heat up faster. No matter the setting, the heat output
(or cooling) is determined by the capacity of the unit.

I was surprised, but I found that a furnace DOES heat up faster when the
thermostat is set higher (at least in one particular case). It seems to be
because of something in the thermostat called the "heat anticipator" that
turns the furnace off sooner.
It was set at 70, but off and the temperature was down to around 50 when
turned on. The furnace ran awhile and turned off around 62. Consecutive
cycles would increase the temperature more.

The heater, no matter the fuel, has a maximum capacity of output. Some
may cycle based on internal sensors that keep the system from
overheating. In a water system, if the heat is not carried off fast
enough it may cycle so the heat exchanger does not overheat.

The heat anticipator does a similar function to avoid the temperature
going above set point. Even though the burner stops, heat from the
surrounding firebox and exchanger will give off some heat so the T-stat
shuts it off early. Accuracy depends on many factors.

[Clare Snyder]

Post by Ed P

Post by Mark Lloyd
[snip]

Post by Ed P
Another mistake some people make is setting the thermostat to an extreme
number. If they want to go from 65 to 70, they set the thermostat to 80
thinking is will heat up faster. No matter the setting, the heat output
(or cooling) is determined by the capacity of the unit.

I was surprised, but I found that a furnace DOES heat up faster when the
thermostat is set higher (at least in one particular case). It seems to be
because of something in the thermostat called the "heat anticipator" that
turns the furnace off sooner.
It was set at 70, but off and the temperature was down to around 50 when
turned on. The furnace ran awhile and turned off around 62. Consecutive
cycles would increase the temperature more.

The heater, no matter the fuel, has a maximum capacity of output. Some
may cycle based on internal sensors that keep the system from
overheating. In a water system, if the heat is not carried off fast
enough it may cycle so the heat exchanger does not overheat.
The heat anticipator does a similar function to avoid the temperature
going above set point. Even though the burner stops, heat from the
surrounding firebox and exchanger will give off some heat so the T-stat
shuts it off early. Accuracy depends on many factors.

SOME 2 stage units will kick up to high if the difference between
ambient and set is more than X degrees - so may heat faster.
My furnace starts at 3500 BTU, and kicks up to 50000 or 52000 after 6
minutes of running?. Mine does not have external air temp input.

[Ralph Mowery]

Post by Clare Snyder
SOME 2 stage units will kick up to high if the difference between
ambient and set is more than X degrees - so may heat faster.
My furnace starts at 3500 BTU, and kicks up to 50000 or 52000 after 6
minutes of running?. Mine does not have external air temp input.

Heat pumps often have strip heaters that come on if the set temperature
is more than about 2 deg higher. So it will heat the house quicker at
the expense of much more electricity.

[Rusty]

Post by Mark Lloyd
[snip]

Post by Ed P
Another mistake some people make is setting the thermostat to an extreme
number. If they want to go from 65 to 70, they set the thermostat to 80
thinking is will heat up faster. No matter the setting, the heat output
(or cooling) is determined by the capacity of the unit.

I was surprised, but I found that a furnace DOES heat up faster when the
thermostat is set higher (at least in one particular case). It seems to be
because of something in the thermostat called the "heat anticipator" that
turns the furnace off sooner.

Beginning the heating cycle *sooner* does not necessarily equate to
heating *faster*. My Honeywell t-stat has the Heat Anticipator feature.
When programmed to begin a heating cycle for, say, 8:00AM, the t-stat
starts the furnace at perhaps 7:30 so that the desired temperature is
obtained by 8:00. My furnace has only two operating modes: on or off.
When it's on, it has a fixed output. It does not heat the house any
faster; it simply begins the heating cycle sooner.

Post by Mark Lloyd
It was set at 70, but off and the temperature was down to around 50 when
turned on. The furnace ran awhile and turned off around 62. Consecutive
cycles would increase the temperature more.

[Bob F]

Post by micky
Avoiding large fluctuations in temperature can be more energy-efficient
than allowing the home to cool too much and then reheating it from
scratch.
This refers to homes in winter.
Discuss. Defend or deny.
https://www.google.com/search?client=firefox-b-1-d&q=avoiding+large+fluctuations+in+temperature+can+be+more+energy-efficient+than+allowing+the+home+to+cool+too+much+and+then+reheating+it+from+scratch.

With a heat pump system, or maybe a variable output furnace, it could be
true. With a single output furnace, it is nonsense. The furnace cannot
"work harder". It has 1 level it works at, and only the time changes.
And clearly, the more the house temp drops as it cools, the slower heat
energy is lost, which makes a big difference. The total time the furnace
runs will be less. It will just run a bit longer in the morning to heat
the air, and cycle a little more early in the day until the structure
warms up.