Setting Back hot water boiler thermostats

Reply

  #1  
Old 01-13-09, 11:35 AM
B
Member
Thread Starter
Join Date: Jan 2009
Location: Indiana
Posts: 11
Received 0 Votes on 0 Posts
Setting Back hot water boiler thermostats

This is my first season with a hot water heating system. I want to know if it pays to set back my thermostat as with a forced air system when I am not home or when I am asleep. I am thinking 5 to 10 degrees for 5 hours or more.
 
Sponsored Links
  #2  
Old 01-13-09, 11:45 AM
1
Member
Join Date: Jan 2009
Location: USA
Posts: 17
Received 0 Votes on 0 Posts
Originally Posted by buffettp View Post
This is my first season with a hot water heating system. I want to know if it pays to set back my thermostat as with a forced air system when I am not home or when I am asleep. I am thinking 5 to 10 degrees for 5 hours or more.
Old-style boiler or new ultra-high efficiency boiler?
 
  #3  
Old 01-13-09, 11:54 AM
B
Member
Thread Starter
Join Date: Jan 2009
Location: Indiana
Posts: 11
Received 0 Votes on 0 Posts
Old style boiler, 15 to 20 years old.
 
  #4  
Old 01-13-09, 05:19 PM
G
Member
Join Date: Oct 2008
Location: USA
Posts: 2,970
Received 11 Votes on 11 Posts
Maybe "Buffettp" was thinking of an outdoor temp reset instead of just turning back your indoor thermostat at night or when you are gone from the house?

No matter what kind of boiler or furnace you have, I think turning down the thermostat would reduce total fuel usage. Of course, when you turn up your thermostat the next morning, the boiler will have to run a while to recover - but, in the meantime, there was lower heat loss from the house.

(If you could somehow measure the total Btu heat loss from the house during the whole winter, that will be exactly the total heat that your boiler needs to provide for the season. So, every Btu you save at night, or whenever, is a Btu your furnace doesn't need to provide.)
Doug
 

Last edited by gilmorrie; 01-13-09 at 05:35 PM.
  #5  
Old 01-13-09, 05:32 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
I believe that with a forced air system the savings would be greater that with hot water. The reason is that the home will 'recover' faster from a setback period.

My general rule is 1/2 degree per hour of setback, not less than 5 hours.

I've done LOTS of testing here at my home over the past 4 years with setback... and I've concluded that in MY home, I don't save enough fuel to offset the discomfort of the cooler temps. But, I DO set back 3 degrees at night for sleeping comfort.
 
  #6  
Old 01-13-09, 06:20 PM
plumbingods's Avatar
Member
Join Date: Apr 2008
Location: Manch-vegas, New Hampshire
Posts: 2,182
Received 0 Votes on 0 Posts
I usually tell my customers not to set back more than 5 degrees, as if you go to far, you lose your savings while trying to bring the heat back up.
 
  #7  
Old 01-16-09, 12:34 PM
L
Member
Join Date: Oct 2004
Location: PA
Posts: 2,034
Received 4 Votes on 4 Posts
Originally Posted by NJ Trooper View Post

My general rule is 1/2 degree per hour of setback, not less than 5 hours.

.
Can you give the mathematically challenged folk a concrete example of that calculation? Does that mean if you turn the stat back for 5 hours it should be only 2.5 degrees lowered?
 
  #8  
Old 01-16-09, 04:30 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Lucky, you can't be _that_ challenged... cuz yes, that's what it means. Additionally, I probably would not set back much more than 5-6 degrees unless I was going to be outta the house for like a week or two ... then I would drop it all the way down to like 55 or maybe even 50, depending on time of year... if I had to leave the house in extreme cold wx conditions, I might not go that low for fear of pipes freezing.
 
  #9  
Old 01-17-09, 06:18 AM
L
Member
Join Date: Oct 2004
Location: PA
Posts: 2,034
Received 4 Votes on 4 Posts
Originally Posted by NJ Trooper View Post
Lucky, you can't be _that_ challenged.
no not that challenged but i wanted to make sure before asking my next question (i have been wrong before!) and making a general point. Since my math was right, that means if i'm away 9 hours a day, thats 4.5 degrees. I'm not dissing you for your generalization(you obviously know more than i ever will about boilers), just trying to show OP it may or may not apply.

And in my system setting back to 62 then having turn back on after 4pm to get to 67 would just not work at all. Id be waiting until midnight lol.

I guess i'm really just trying to tell the OP he needs to actually test things out on his system, all ours are different. And by giving my example, wanted him to know a rule of thumb is not the same on every thumb I'm definitely the exception.

If he has a quick recovery, then definitely a setback would save money and I'd do it. But in my system, i never could set back 5 degrees on a daily basis.

Of course 'testing' out a system by turning it down and measuring recovery time isnt the most exciting thing in the world. But a few days of testing will definitely enable the OP to see the best course of action for the system in question.
 
  #10  
Old 01-17-09, 07:00 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
I understand... and you are correct.

That's why I often say, "Your Mileage May Vary" ... I get kinda tired of saying that, and ppl get tired of hearing it, so sometimes I don't...

Of course one should do what is best for THEIR circumstances.

Like Mark, I probably wouldn't recommend more than a 5 degree setback for ANY daily situation. Even if it went out to 12 hours... (6 by my 'rule'), but most daily schedules call for less setback than that.

So, let's re-state the rule and expand on it a bit:

One half degree per hour of setback. But no setback period less than 5 hours. And not more than 5 degrees of setback on a 'daily' schedule.

(obviously, most t'stats can't set a half degree, so round up or down, your choice)

Longer setback periods such as a week or two vacation should be setback to the minimum temperature that can safely exist. For example: don't set it so low that pipes freeze and house plants die.

YOUR MILEAGE MAY VARY!

How's that Lucky? clear enough?
 
  #11  
Old 01-17-09, 10:47 AM
B
Member
Thread Starter
Join Date: Jan 2009
Location: Indiana
Posts: 11
Received 0 Votes on 0 Posts
Thanks guys. My system can recover 8 to 10 degrees in about 2 hours. Except in the coldest weather, I can set it back and it only loses 2-3 degrees an hour. My typical daily schedule is it is setback to 58 at night. It cranks up to 68 at 4am which has it at temp at 6 am when I get up. It then sets back to 58 at 7am so it is still warm enough when I leave at 8am. It then cranks back up at 4pm and is up to temp by 6pm.

As I have stated I have had people tell me that turning it down and back up takes more gas than leaving it turned down. If it is just a comfort issue, then I am fine, but if there is an issue with it using more gas to turn it down so much, then I have an issue.
 
  #12  
Old 01-17-09, 11:18 AM
L
Member
Join Date: Oct 2004
Location: PA
Posts: 2,034
Received 4 Votes on 4 Posts
Originally Posted by NJ Trooper View Post
I understand... and you are correct.

How's that Lucky? clear enough?
we need to get signatures on this board. That would make a good one for me It's just i look at things thru the eyes of a newbie and see things that more experienced people dont. It's a curse I know, finding exceptions.

Originally Posted by buffettp View Post
Thanks guys. My system can recover 8 to 10 degrees in about 2 hours. .
Well i dont have the math to prove it, but if it only takes you 2 hours to get up 10 degrees, i'd definitely utilize setback to some degree. Purely an intuitive thing on my part. I may be wrong. But thats a lot of heat in cold weather to keep the house at if no one is home. My thinking would be keeping 10 degrees cooler for 8 hours more than makes up for even a 2 hour 'solid' run to get back up to temp.
 
  #13  
Old 01-17-09, 01:46 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Unfortunately, it takes a bit of data collection to 'prove' whether a particular setting is more or less economical. There are so many factors that affect the outcome... of course outdoor temp is one, heat loss of the home another, mass of the structure, etc, etc...

One could 'clock' their gas meter or oil burner and measure the actual fuel useage and collect degree day data ... these two data sets are enough to get a rough idea of savings, but one would have to collect this data over a long enough time period to be able to filter out the 'noise' in that data. Then, do some simple comparisons.

Data 'noise' would include sunny vs cloudy, windy vs calm... if one were A.R. enough, that information could be collected also and used in the analysis.

But who has the time or inclination to do all that? ... uhhhh... me!
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: