Repost From Radiant Forum; Installing temperature differential switch

Sgancarz

I have a Peerless MI series boiler installed in my house with traditional cast iron radiators.  The house was built in 1910 and is fairly large with minimal insulation.  It still contains all knob and tube wiring so I can't insulate until I have rewired the entire house.  My gas bills are obviously quite high and I was looking for a way to reduce those bills a little until I can rewire and insulate.



I keep the thermostat pretty low (63-65) during occupied hours and set back to 60 at night and when away from the house.  When the boiler kicks on after a setback it will run for quite a while until the thermostat is satisfied.  With that the radiators will get extremely hot. 



I just installed a surface mount temperature differential switch on the return to the boiler (this past week).  I have it set to 120 degrees with a 10 degree fixed differential.  Once the return temp reaches the set temp it will shut down the burner, but the pump will continue to run.  Once the return temp drops 10 degrees the burner kicks back in.  I sat and timed it when first installed and it takes about 20 minutes for the temp to drop the 10 degrees and another 20 minutes to rise back to the set temp.



My question is;

1.  Do you think this will reduce my fuel costs?

2. With this low of a return temp, will I run into problems with condensing of the boiler?

NRT_Rob

what?

No, and Yes.



Why are you doing this???



If you have a leaky house, set it back deeper than 60 if you can and use programmable thermostats to start recovery earlier if need be. Setbacks are big savings in leaky homes.



Then let the boiler do its thing to get back up to temp. If you are trying to reduce boiler temps or something, you need an outdoor reset control not an aquastat, and you still need to watch out for boiler protection issues.

Mark Eatherton

Guaranteed boiler death...

The control you installed is going to guarantee that the non condensing appliance is going to condense. You MUST have a return temperature above 140 degrees F in order to avoid the long term production of condensate.



I agree with what Rob said. Get rid of the aquastat. You may be saving fuel, but at the expense of human comfort and your boilers life expectancy.



ME