With a mod/con boiler should there be any night setback ?

seandarcy

I'm a new home owner with the Weil-McLain Ultra 2 230. The previous owner had no outdoor thermometer and just set outlet temps at 180. I had an OAT installed, and set the reset curve (actually a straight line!) from [ outdoor 70 > outlet 80 ] to [outdoor 16 > outlet 160 ] . I also reduced the boiler firing rate to 60% by setting the fan rate to 3400 rpm.

Now the question is about night setbacks. Day room temp is 68. Night (11pm to 7am) temp is 62. The thermostat is smart enough to call for heat before 7am , about 5am.

We're only talking about a 6 deg setback. It seems to me I'm better off having the setback, because then I have a constant call for heat from 5am to 7am, much better than cycling through the night.

My evil brother-in-law says I'm just wasting gas reheating the house, and it would be more efficient to keep a constant 68.

What say ye ??

Jamie Hall

And ignore advice from general internet sources, which is almost all based on forced air heat -- a completely different critter! As @Hatterasguy says, it depends so much on the individual building and system that generalisations are dangerous at best.

Boon

Does the WM Ultra offer data logging or stats? Maybe consider doing some data logging and determine if set back vs non-set back saves you any money.

I am on the comfort side of the debate and don't see the value in the set back. If/when I wake to pee in the middle of the night - or heaven forbid #2 - I do not want 62 degree anything. Also I find a colder room to be bothersome when I'm having a restless night.

gschallert

> @Boon said:
> I am on the comfort side of the debate and don't see the value in the set back. If/when I wake to pee in the middle of the night - or heaven forbid #2 - I do not want 62 degree anything.

Lol...I so did not need that mental image. 8-/

Paul S_3

I say no setbacks at all.....this is from experience comparing customers bills

Ironman

I agree that generalizations may not cover your specific scenario, but without knowing all the details about your house, which would envolve long term monitoring, generalizations are all that can be given.

Here's a particular that I've gotten directly from German engineers (they don't use setback over there): mod/cons operate the most efficiently when they run at their lowest firing rate with the lowest return water temp for as long as possible. Americans minds are still fixed on bang-bang technology (100% on, 100% off), therefore, we think that keeping it turned off for as long as possible saves energy. That kind of thinking needs to be abandoned when you have a mod/con. It's exactly the opposite of how the boiler is designed.

The Europeans developed this technology and they've been doing it for almost 40 years. We just showed up at the party in the last 12 - 15 years and most of us still cling to our old way of thinking.

Other variables, as Hatt mentioned, are the type of emitters that you have and how tight the envelope of you house is.

Data logging, in general, is useless with a mod/con unless it shows the actual amount of fuel consumed. Actual run time hours prove nothing because they don't indicate at what rate the boiler was firing.

nicholas bonham-carter

I believe that with no setback, lower constant temperatures can be just as comfortable.
A constant 66 degree setting may get the job done, instead of 72-64, (your mileage may vary!). --NBC

Paul48

There is nothing more efficient than a boiler that is not running. If the homeowner determines that heat is required, then the German engineer's logic applies. If, with night set back the homeowner is satisfied with the efficiency and comfort provided by his system, then go for it. If the homeowner is concerned with efficiency, at all times, you have to caution them that this may not be the case with set back.

Jim Hankinson

One thing I did not see in any of these comments has to do with what happens to water when it is too cold for too long. I thawed too many heat pipes in too many cold locations because the homeowner wanted to save a few bucks.

Personally we have never used setback. If the wife is cold, she can't sleep. If she can't sleep.....

NY_Rob

It doesn't have to be all-or-nothing either....
You can use a mild 2-3deg setback in the sleeping area if you prefer slightly cooler temps for sleeping and don't use any or deeper setback on the other zones if you don't want to.
You need to experiment in your particular home... it can take a bit of tweaking to get it right.

Jean-David Beyer

I have a W-M Ultra 3, and the outdoor reset is connected up.
All my experience is with one house with one boiler.
The old one was oil fired, single temperature, with baseboard upstairs and radiant slab at grade downstairs.

I converted the upstairs to be a second heating zone, and put 14 foot long baseboards in each room. And each zone has its own reset curve. And after a lot of fiddling around, I got the reset curves to be very close to the actual heat loss. I.e., it supplies barely enough heat to maintain the desired temperature. During the cold part of the heating season, the system runs 12 to 18 hours per day. Less during the warmer parts of the heating season.

Now as far as I can tell, it never makes sense to do setback with a radiant slab at grade because it takes 12 to 24 hours to stabilize the system after a temperature change -- either up or down. It takes a really long time to change the temperature of that slab.

But in the baseboard zone, it also makes little sense to do setback because it takes almost all day to recover from a night's setback. The Ultra 3 (I do not know about the Ultra 2) has an option where if a zone is not satisfied after a time, it raises the supply temperature 10F. That helps a little. Then my baseboard zone can recover from a 2F setback in about 4 hours.

So for me, a simple on-off thermostat in each zone will work just fine -- with no setbacks. I imagine the energy saved by supplying only the heat actually required instead of 180F all the time, more than makes up for what might be saved with setbacks. It is my impression that the outdoor reset saves most of the money even though I get some savings by condensing too. Slab gets supply 80F up to 130F, and the baseboard gets 120F to 150F (at 0F outside). Most of the time, it condenses all the time.