How far to set back?

Geno_15

It's time to look at the house, you have one of the best systems. 10* is asking alot from an old house. How are the windows, attic and wall insulation, leaks, infiltration, doors, etc?? I had an old house and we tightened it up as much as possible but I did not want to lose character so we left the weighted windows and clapboard siding. Try running 65*-70*. Most pros will tell you maintaining temp is cheaper depending on the house and how many hours a day you are there.

Also you say 1 zone but how big is it?? Is it old pipes uninsulated??, cast iron radiators?? Multi zones is the way to go but may not be feasible.

Daniel Silver

How far to set back?

I recently purchased a 1930s home in New England which still had its original Gurney coal-fired steam boiler. It was converted to oil-fired hot water some time ago, but needless to say, still not very efficient by modern standards so I replaced the entire system with: Buderus G215 boiler, Riello 40/F5 burner, Taco switching relay, Grundfos 3-speed circulator, air separator and all the usual valves, expansion tank, etc. Domestic hot water is provided by Crown Mega Stor indirect stainless steel tank with a separate Grundfos circulator. I opted not to buy the Buderus Logamatic outdoor reset control, and instead have a standard Honeywell L8148A aquastat. Both circulators are on the return side. I have a single heating zone, but the Taco switching relay has the heating and DHW wired as two separate zones. I use a Honeywell programmable set back thermostat. The steam radiators were replaced some time ago with convectors, but the asbestos-insulated mains in the basement are still big old steam pipes.

Despite the 86% efficient Buderus, I am finding that it still takes 1.5+ hours to heat the house to 72 from a cold-start set back of 10 degrees. My thermostat is programmed to 72 at 6 in the morning, and then set back at 8 when I leave the house, then back up to 72 at 6 in the evening, and set back at 11:30 bedtime. Each time the boiler starts recovery from setback, the house is pretty cold, about 62-63 degrees, and the boiler is basically recovering on a cold start. The boiler runs straight for about 1 hour to get warmed up, before it even begins to cycle.

My question is, can I achieve any better fuel efficiency by setting back only a little bit, so that the system stays relatively warmed up all the time, rather than going all the way back to a cold start twice a day? Is there anything else that will help efficiency (aside from getting rid of the big mains?) What about a dual-cycle thermostat? Circulator speed settings? How can I tweak the system to get the most out of this beautiful new boiler? Thanks.

Daniel Silver

How far to set back?

I recently purchased a 1930s home in New England which still had its original Gurney coal-fired steam boiler. It was converted to oil-fired hot water some time ago, but needless to say, still not very efficient by modern standards so I replaced the entire system with: Buderus G215 boiler, Riello 40/F5 burner, Taco switching relay, Grundfos 3-speed circulator, air separator and all the usual valves, expansion tank, etc. Domestic hot water is provided by Crown Mega Stor indirect stainless steel tank with a separate Grundfos circulator. I opted not to buy the Buderus Logamatic outdoor reset control, and instead have a standard Honeywell L8148A aquastat. Both circulators are on the return side. I have a single heating zone, but the Taco switching relay has the heating and DHW wired as two separate zones. I use a Honeywell programmable set back thermostat. The steam radiators were replaced some time ago with convectors, but the asbestos-insulated mains in the basement are still big old steam pipes.

Despite the 86% efficient Buderus, I am finding that it still takes 1.5+ hours to heat the house to 72 from a cold-start set back of 10 degrees. My thermostat is programmed to 72 at 6 in the morning, and then set back at 8 when I leave the house, then back up to 72 at 6 in the evening, and set back at 11:30 bedtime. Each time the boiler starts recovery from setback, the house is pretty cold, about 62-63 degrees, and the boiler is basically recovering on a cold start. The boiler runs straight for about 1 hour to get warmed up, before it even begins to cycle.

My question is, can I achieve any better fuel efficiency by setting back only a little bit, so that the system stays relatively warmed up all the time, rather than going all the way back to a cold start twice a day? Is there anything else that will help efficiency (aside from getting rid of the big mains?) What about a dual-cycle thermostat? Circulator speed settings? How can I tweak the system to get the most out of this beautiful new boiler? Thanks.

Ron Schroeder_2

Hi Daniel,

That'ts a pretty big setback. You probobly wouldn't gain or loose much in oil usage with a smaller setback but it might be more comfortable.

Do you have any idea how close your boiler is sized to the houses load?


Ron

Joe@buderus

Setback

I agree the set back may be too much for the older home to recover from. Based on your discription no more than five degrees might work better.

Would also suggest consulting with the installer with regards to the boiler running for so long before heat is transfer to the home.

Daniel Silver

Hmmmm....I truthfully do not know the calculations that my HVAC contractor made when sizing the boiler. He took a lot of raidator measurements, etc. My impression is that the Buderus G215 is for large residential and small commercial use, and the HVAC contractor determined that the output was suitable to handle the volume in the house. It does not hold very much water itself, and I suspect much of the water is contained in the pipes. It certainly seems nice and warm once the system gets up to speed, and it handles the DHW extremely well. As far as looking at the house, I have relatively new double-hung windows on the entire house, and full attic insulation, but nothing in the walls.

John Morrill_3

some key items overlooked

What temp is the aquastat set for? Your building will take longer to heat up if it is trying to do so at only 130F or so.

Check your convectors for air (bleed them if you haven't recently). Check the convectors for good air circulation, too.

The boiler is staying on for a long time because the water loop is busy losing Btus to the space, so it has to make them up. This alone is not necessarily a sign of system inefficiency, and you are saving $ with that setback, the issue is one of comfort and time of recovery.

I have a 1930s-era home w/o insulation in the walls, and once the cold sets in, it takes a while to bring it back. I do have outdoor reset, so when the indoor temp gets low for one reason or another I goose the temp manually to speed things up, then return it to its 'normal' auto set.

For comfort, you could probably decrease your setback to 5-8 degrees, but do check the aquastat setting, and also how well your convectors are giving off heat.

Daniel Silver

Thanks for the info. I bled and vacuumed all convectors when the system was installed, and I have also experiemented with different aquastat settings and circulator speeds. So far changing the circulator speed does not seem to make much difference. I decided to keep the aquastat at 180-190 because anything lower was not heating the convectors very well.

Ron Schroeder_2

Hi Daniel,

You can get some idea of how closly matched your boiler is to the heating load by measuring how long it runs and how long it is off at a steady thermostat setting on a cold night.

One problem with too much setback is the house is still cold for a while even after the air inside warms up so you have to have a little hotter air temperature for a given feeling of warmth.

Ron

Daniel Silver

Ahhh, I have been keeping an eye on this very thing, to see if I could do some simple calculations of fuel usage. On a recent cold night the boiler seemed to cycle for about 7 minutes, about every 20 minutes or so. Tonight will be cold again so I will check this again a bit more carefully.