New Thermostat

paul77

Hi all,



I replaced my 20 years old mechanical thermostat with a Honeywell VisionPRO TH8000.  The problem I am having is that this new thermostat is so sensitive that  it will turn off the heat when the radiators are half hot.  I have CPH set at 1 and change function 680 has no effect.  I have a single pipe steam system, is there are way to fix this problem?  

FJL

Halfway Hot Rads

Why is that necessarily a problem? If the t-stat is satisfied, presumably the space has been warmed to the desired temperature. Or is it that the room temp reaches the desired temp where the t-stat is located, but not in other rooms?

paul77

New Thermostat

You have a good point there.



All my radiators are half hot when the thermostat shut the boiler off.

To me this is a big wast of gas.  Is there a solution to my problem?

TomM

swing

the th8000 doesn't have a 'swing' function does it?

nicholas bonham-carter

wasting gas?

wouldn't it be wasting gas, if it continued firing the boiler beyond the set temperature?--nbc

Jamie Hall

The question isn't...

are the radiators hot all the way across -- the question is, is the space at the desired temperature?  If the space is at the desired temperature, there's no point whatsoever in continuing to run the boiler until the radiators are hot across.  All that would do is raise the space temperature above the set temperature -- which would indeed be a waste of fuel.



Most of the time, in fact, you don't need the full output of the heating system (radiators hot all the way across) to maintain an even space temperature.  Where you do need it is on a design temperature day, or in bringing the space up to temperature from a setback.  Then, maybe, you will get the radiators hot all the way across.  Otherwise, no.  In fact, when you think about it, you really shouldn't -- if it takes the radiators hot all the way across on a normal sort of early winter day to maintain your space temperature, you're going to be mighty chilly on a design day.



Does this waste fuel?  Yes it does, some.  Which is why quoting a single figure for the efficiency of a heating system is just silly.

paul77

New Thermostat

No this unit does not have a swing adjustment.



It is wasting gas because it burns a lot of fuel to bring the unit to steam just to heat up half of a radiator. 



 Is there a Thermostat that has Swing and CPH adjustment?

What thermostat do you guys recommend for single pipe steam system?

Jamie Hall

I should perhaps add

to my previous post, in view of the comments on the swing adjustment (which is available on some thermostats, but not all).



Yes, if the swing is adjusted properly, you can save energy costs since the boiler will run long enough to raise the space temperature from the bottom of the swing range to the top of it.  This will save the cost of the fuel necessary to bring the boiler water back to boiling which is otherwise seen in situations where the radiators do not heat all the way across.



However.  Do you really want this level of hair shirt?  For the building which I superintend (a house museum), I would need to use a swing of about 4 degrees to do this on average sort of day.  That is to say, if the set point were, let's say, 65, the thermostat would not call for heat until the temperature had dropped to 61.  (Note that this figure has been checked -- carefully -- while evaluating the benefits -- or lack of them -- of setbacks).  On a very cold, or very windy, day, the appropriate swing would be on the order of half a degree or so, and the boiler would run roughly once an hour, long enough to fill the radiators (and, incidentally, just long enough to trip the vapourstat which is set at 7 ounces cutout).



Now my situation is somewhat biased by the fact that many of the objects in the house do not take kindly to temperature swings of that magnitude (pianos, for example, or oil paintings are very sensitive to temperature swings).



But on the whole, I think it very much worthwhile to balance the energy savings involved in wide swings (or setbacks -- much the same thing) with comfort.  In my particular situation, going to a wide enough swing (which I would have to reset daily, by the way) would save on the order of a dollar or so of oil every day -- say 10 gallons per month (I burn over 2,000 gallons per year).



Is this level of energy conservation effort worth it?  Everyone has their own preferences; for me, the answer is a resounding no...