Thermostat swing for less frequent, longer boiler cycles times

jgvasa

Our single pipe steam system (with a 2011 Burnham gas fired boiler) is controlled through a Lux PSP511LCa thermostat. Previously, we had issues with the second story of our home always being colder than the first floor (poor insulation). The second floor radiators would get somewhat hot, but not enough to sustain heat between cycles. Average cycle rate for the boiler kicking on was around 1 cycle per hour

The way we've recently corrected that is by adjusting the "Swing" of our thermostat. We discovered it was previously set to "1", which is a 0.25 temperature swing. I've changed this to "4", which is a 1 degree swing. With the thermostat set at 69 degrees, the thermostat kicks on at 68 and turns off at 70. This keeps our house much warmer than it's ever been, due to how hot the radiators get now, and therefore stay hotter longer between cycles. With a 1 degree temperature difference, if I'm up and moving around, I'm sweating by the end. The wife loves it though.

This 2 degree difference of course, causes the boiler to run much longer between cycles, which ends up being around every 2 hours. I've seen on here that typically 1 cycle per hour is recommended, but with this current setup, 1 longer cycle every 2 hours leaves our house feeling significantly warmer for longer, and in between cycles. I would guesstimate that over the course of a day the total run time is around the same or slightly more as before.

Given that I've seen 1 cycle per hour being recommended so much here, are there any downsides from a maintenance perspective to running our steam boiler system at less frequency, with much longer cycles? Would this expect to "net" the same wear, and gas utility expense?

ethicalpaul

The reason you see 1 cycle per hour is in opposition to more times per hour (like forced air would be more times per hour). Fewer times is no problem, but really the cycles per hour is just an approximation. The swing is the real driver in the thermostats I've seen.

How fast are the vents on your downstairs radiators? Slow them down to force more steam upstairs.

Also make sure your main venting is good.

jgvasa

@ethicalpaul Main venting is massive - installed by NE Steamworks. All of our vents are Vent-Rite adjustable's. We have the first floor (near the thermostat) set at 4-5, upstairs set at 7-8. Despite only being a 1 temperature difference, increasing our swing to 1 degree has made a massive improvement in our home heating comfort (and bumping the thermostat from 68 to 69). Just want to pay the price of less longevity, or sky-high gas bills

Fred

It sounds to me like you are trying to use your thermostat to balance your steam system. My guess is, if you have a thermometer on the first floor to measure temperature you will find the downstairs temp is likely a degree or two higher than you think because of the broader swing and costing you more money for fuel than you may think. The reason you only get one cycle every two hours is because those cast iron radiators continue to "radiate" heat well past the time the boiler shuts down and will over-shoot the set temperature. The thermostat isn't going to call for heat until the room temp drops to a range recognized by the thermostat as a "call for heat". Forced air heating and electric systems don't have the mass to do that. Typically, most thermostat manufacturers will program their products at "1" for steam, "2" for Hot water systems, "3" for natural gas Forced air and "4" for electric heat. Some Steam homeowners find that 2 cycles per hour works better for them than 1 but the swing is probably not very comfortable at 3 or 4. You'd be surprised how noticeable a degree makes in comfort level. I think what @ethicalpaul said is most appropriate. Spend the time to balance your steam system by adjusting the venting at each radiator/room so that you get the temp you want on both floors. Slower venting on the first floor, faster venting on the second floor but first make sure you have the appropriate venting on your mains. team will take the path of least resistance, meaning if your main vents aren't properly sized, the steam will go to radiators where the venting, on those radiators make it easier to flow.

jgvasa

Thanks for the response @Fred . You're right about the thermometer - I have one right next to our thermostat. Thermostat is at 69 degrees, thermometer reads 70. So rather than adjusting swing, are you suggesting that simply increasing the temperature by ~1 degree, and lowering the swing back to 0.25 - 0.5 degrees would achieve a more energy efficient outcome with the same comfort? (assuming vent balance is all in order)

Fred

@jgvasa The real question is (actually a couple questions) 1. What temp do you really want? and 2. How much temp variance is there between the first and second floor? I personally have my thermostat set at 1CPH and set the room temp exactly to what is comfortable for me and I have my second-floor radiator vents slowed down enough that the second floor stays a couple degrees cooler because I like sleeping in a cooler environment. If I were you, I'd start out with a "2" setting and see how much you over-shoot the thermostat and how much difference in temp there is between the first and second floor. Do you have adjustable radiator vents like the Hoffman 1A or another brand adjustable or are your radiator vents the fixed venting type? The fine tuning is truly trial and error until you are happy and comfortable. Another factor is your location. Where are you? It is next to impossible to make good adjustments until you get past the "shoulder" season where outside temps are moderate and don't really represent the real winter temps. In the shoulder season, the boiler just isn't going to run long enough to fully represent how the boiler/inside temps will be in colder weather.