I have a two story colonial that was built in ~1920 or so. Has a gas fired
boiler with cast iron radiators. I have been turning the thermostat down
about 4-5° each night and leaving it at that setting until I return home
from work the next afternoon. On the weekends we turn it up when we rise,
and back down 4-5° at night. It takes about 1-2 hours to bring the temp.
back up those 4-5°
I'm wondering if I might be better off just leaving it at one setting? I
couldn't find much info on this...maybe not looking in the right place.
You could buy a set back thermostat that will do all this automatically.
Honeywell has the easiest ones to use, others are cheaper. Make sure it's meant
for hot water rads. It can even start up prior to 'wake-up' time to make sure
the home is warm.
The recovery time for five degrees seems like a lot. Has the house been
insulated and the heater upgraded? My heater can recover that in about 30
minutes or less.
Consider a programmable thermostat. You can have it raise the temperature
before you arrive home or get up in the morning.
In any case, you are still saving. I don't recall where I saw it, but there
are available figures on what you can save.
Since we can't see it, there is no telling what the origonal system looked
like. I'm almost ready to bet it's a converted gravity system. That could
cause the recovery time to take so long....
Energy wise you are doing the right thing. A programmable thermostat
will allow the system to be up to temperature by the time you get home.
That 1-2 hours seems like it is a lot. I don't know water based heat
systems, buy you may want to check into that issue.
Hot water cast iron radiator systems are very slow, both to heat up and to
cool down. Depending on how high a temperature the boiler aquastat is set
for, 1 - 2 hours may not be unusual in a non-tight house. Although our
house is older than the 1920s, I assume our heating distribution system with
large cast iron radiators dates back to about then. We have our thermostat
set to end the offset about 75 minutes before we get up. And we have it set
back at night at least two hours before going to bed.
"Joseph Meehan" <sligojoe email@example.com> wrote in message
And you might save more with a larger capacity furnace (or AC) that lets
the house cool longer to a lower setback temp before it must begin to
warm it up again.
A more programmable "comfortstat" with a forced-air system might save
even more energy by only starting the warmup when you get home, with
a higher initial room air temp to precompensate for initially colder
walls, according to the new ASHRAE 55-2004 comfort standard, as in
the warmup schedule below.
10 DEF FNPS(T)=EXP(16.6536-4030.183/(TA+235))'sat vapor pressure, kPa
20 VEL0/196.9'air velocity (m/s)
30 RH@'relative humidity (%)
40 ICL=.155*1.1'clothing resistance (m^2K/W)
50 M=1.4*58.15'metabolic rate (W/m^2)
60 CROOM 00'room thermal capacitance (Btu/F)
70 UROOM=1.5*1200'room cap airfilm conductance (Btu/h-F)
80 TRFU'inital mean radiant temp (F)
85 TAF€'initial air temp est (F)
90 FOR MWARM=0 TO 90'warmup time (minutes)
95 TRF=TRF+(TAF-TRF)*UROOM/60/CROOM'new radiant temp (F)
96 TR=(TRF-32)/1.8'mean radiant temp (C)
110 TA=(TAF-32)/1.8'air temp (C)
120 PA=RH*10*FNPS(TA)'water vapor pressure, Pa
150 FCL=1.05+.645*ICL'clothing factor
160 HCF.1*SQR(VEL)'forced convection conductance
170 TAA=TA+273'air temp (K)
180 TRA=TR+273'mean radiant temp (K)
190 TCLA=TAA+(35.5-TA)/(3.5*(6.45*ICL+.1))'est clothing temp
200 P1=ICL*FCL:P2=P1*3.96:P3=P1*100:P4=P1*TAA'intermediate values
240 XF=(XF+XN)/2'natural convection conductance
260 IF HCF>HCN THEN HC=HCF ELSE HC=HCN
280 IF ABS(XN-XF)>.00015 GOTO 240
290 TCL0*XN-273'clothing surface temp (C)
300 HL1=.00305*(5733-6.99*M-PA)'heat loss diff through skin
310 HL2=.42*(M-58.15)'heat loss by sweating
320 HL3=.000017*M*(5867-PA)'latent respiration heat loss
330 HL4=.0014*M*(34-TA)'dry respiration heat loss
340 HL5=3.96*FCL*(XN^4-(TRA/100)^4)'heat loss by radiation
350 HL6üL*HC*(TCL-TA)'heat loss by convection
360 TS=.303*EXP(-.036*M)+.028'thermal sensation transfer coefficient
370 PMV=TS*(M-HL1-HL2-HL3-HL4-HL5-HL6)'predicted mean vote
380 IF ABS(PMV)>.1 THEN TAF=TAF-PMV: GOTO 110
390 IF MWARM MOD 10 = 0 THEN PRINT 500+MWARM;"'";TAF,TRF,PMV
400 NEXT MWARM
Warmup Room air Mean radiant Predicted mean vote
time temp temp 0 <-> "comfortable"
(min) (F) (F) on a -3->+3 scale
0 77.38742 55.375 9.372071E-02
10 76.3209 58.39394 9.864321E-02
20 75.37932 60.83982 9.903763E-02
30 74.54995 62.8239 9.377487E-02
40 73.9352 64.43015 9.468317E-02
50 73.41834 65.73348 9.436616E-02
60 73.01363 66.7851 9.688769E-02
70 72.71077 67.63396 9.948866E-02
80 72.40714 68.32138 9.704017E-02
90 72.2062 68.87712 9.865938E-02
M > I have a two story colonial that was built in ~1920 or so. Has a gas fired
M > boiler with cast iron radiators. I have been turning the thermostat down
M > about 4-5° each night and leaving it at that setting until I return home
M > from work the next afternoon. On the weekends we turn it up when we rise,
M > and back down 4-5° at night. It takes about 1-2 hours to bring the temp.
M > back up those 4-5°
M > I'm wondering if I might be better off just leaving it at one setting? I
M > couldn't find much info on this...maybe not looking in the right place.
I would think part of the answer is are you comfortable during the
re-heating period. If it is occurring during your "wake up period"
then might no be too bad. (IOW you have a setback thermometer, it
starts to heat the house back up at 5 a.m. and your alarm is set for 6
We have a digital thermostat and find turning down the thermostat one
degree at night is sufficient and confortable (from 68ø to 67ø).
..FWIW the non-digital thermostats (the ones with the mercury bubble
attached to a coiled spring) have around a 6ø 'knee' and can be
¯ barry.martinþATþthesafebbs.zeppole.com ®
* ClientSez: Memory? Is that the RAM stuff?
þ RoseReader 2.52á P003186
þ The Safe BBS þ Bettendorf, IA 563-359-1971
We have two zones....both have the round Honeywell mercury type t-stats. And
they both have around a 4° 'knee' as you call it. If I set the stats at 60°,
the house is actually around 64°. We bump it up to 64, and it keeps it right
around 68°. So I guess the programmable stats would allow us to have the
house warmer when we get up in the morning and when we arrive home in the
evening, but they would essentially do the same thing we do manually now.
As others have replied, a programmable thermostat would be a good, fairly
inexpensive, simple to install solution. I would also suggest you look at
the temperature setting on your circulating hot water heating system-- on
the furnace. With cast iron radiators you should have the water at about
180 degrees or so.
This is Turtle.
Here is the old take on turning off heating or cooling systems for any length of
1 Minute to 4 Hours off tinds to cost you a little money on cost to operate.
4 Hours to 8 Hours off tends to save a little or even break even on cost but
most of the time it will save a little.
8 Hour or + Off will save some good money on fuel cost. Any off time 8 Hours or
more will save some good money.
Now if you just turn it off all the time it will save a bunch of money.
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