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Joined on November 14, 2009

Last Post on July 16, 2014

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Facilitating maintenance of P-trol & V-stat

@ December 27, 2013 7:10 PM in An Epic Tale: I hear the Trane a comin'!

Hi Colleen,

To facilitate maintenance of your pressure controls, one inexpensive and fairly easy thing to do is to install a union between the pigtail and the pressuretrol (or vaporstat). This will let you remove the control and do whatever maintenance you need to, just make sure to leave enough slack in the wiring.

Here's a front-on pic of the pressure instrument stack on my boiler. Pressuretrol (high pressure safety limit) is on the right, low pressure gauge and Dwyer pressure switch (control limit) are on the right. You can see the placement of the unions on each. There's a ball valve on the right side to isolate the low pressure devices when performing a blowdown. Note that there's not a ball valve on the pressuretrol side - having one would effectively disable the safety control and would (I'd hope) be failed by an inspector.

Nest Learning and Logging

@ December 22, 2013 7:03 AM in My opinion of NEST on steam

Chris, from what I gather from the Nest website and user comments, it can take a while for it to learn your system and your occupancy pattterns. One person commented that it took more than a week for Nest to learn their radiant system, but after that it performed well, or at least well enough for that user.

As for data display and logging, remember that the Nest guys are orignally from Apple, and Apple is notorious for deciding for you what you need to see and what you get to control. The Nest does do data logging, which is accessible from the iPhone/iPad app, but there again the content and format of the reports is pre-determined for you.

Changing CPH

@ December 21, 2013 11:33 PM in Running 2 CPH finally and loving it!

The weather here was mild too. Is it possible that the temperature reached setpoint before steam got to the radiators? Are there other heat sources that could have affected the thermostat?

Not sure how changing the CPH ("heat cycle rate" function 0240 in the VP installer setup guide) would affect the algorithm in the thermostat. Might reset it so that it starts re-learning from scratch, or could just confuse it. I'm not sure even Honeywell knows what happens.

The problem with these thermostats is despite all their smarts, they can't tell the difference between heating the mains and heating the radiators.Their heat calculations wrongly assume that steam is ready at the radiators when they signal a call for heat, and most of the time it just ain't so. It's a shame, because all it would take is a $3 snap-disc thermal switch mounted at the end of the main to indicate mains hot or not. It's only one data point, but it tells you a lot about what's going on with the system.

Heat Loss

@ December 18, 2013 5:20 PM in Running 2 CPH finally and loving it!

You'll get a much better idea of your actual heat loss if you download the free Slant-Fin heat loss calculator software and spend some quality time feeding it the numbers it needs.

Windows version

Android/iPad version


@ December 14, 2013 11:26 AM in Running 2 CPH finally and loving it!

The other nice thing about mechanical relays is that you don't have to be concerned with the type or amount of the voltage you're switching, as long as it's within the relay's specs. And switch contacts are much better at surviving transient power surges that would fry a transistor output.

Solid State

@ December 14, 2013 10:09 AM in Running 2 CPH finally and loving it!

Yes, the output relays are mechanical. The rest is all solid state, even the digital inputs. Odd thing is though, TECO has a version of the SG2 with transistor outputs making the whole thing solid state.

TECO SG2 on eBay

@ December 14, 2013 9:30 AM in Running 2 CPH finally and loving it!

There are a bunch of used 12 volt DC TECO SG2 units available on eBay for $60 apiece. These go for $145 new. Each has 8 digital inputs, 8 digital outputs, and 4 analog inputs. Link: TECO SG2 on eBay

You'll also need to spring for a $33 programming cable from FactoryMation. Link: Programming cable


@ December 12, 2013 6:18 PM in Running 2 CPH finally and loving it!

PMJ, if I remember correctly you're using the TECO SG2, yes? I just started working with one to see how much of my heat loss algorithm and burner modulation I can pack into it. I'm doing a fair bit of math so the function block diagram is easier to work with than ladder logic. Nice that it can do either, especially at the sub-$100 price point, though I wish you could mix the two since cycle control logic is better suited to ladders. The current version of the SG2 includes PID algorithm function blocks, and they even have an 0-10 vdc analog output expansion module at a great price (though it's out of stock at the moment). About the only thing missing is historical data collection which you won't find at this level of hardware, and setback scheduling which can be managed by the wall thermostat.

Cut-Out / Cut-In

@ December 12, 2013 6:19 AM in Running 2 CPH finally and loving it!

MDN, I'm curious what your cut-out and cut-in pressures are, and how long it takes for the pressure to drop to cut-in. Also what your temperature swing is when running in that mode.

Steam coming

@ December 11, 2013 10:54 PM in Running 2 CPH finally and loving it!

From those numbers, your preheat time is 3:10. How long is/are your main(s)?

What's "steam coming", when the main at the boiler is hot?

Thermistor or Snap-Disc switch

@ December 11, 2013 10:50 PM in Running 2 CPH finally and loving it!

A thermocouple is a bit overkill for this application. I'm using a (much cheaper) 10K thermistor to detect steam at the end of the mains, but a 160 degF snap-disc temperature switch would do just as well. You don't really need to know the precise temperature at the end of the main, just that it's hot.


@ December 11, 2013 10:13 PM in Running 2 CPH finally and loving it!

"Preheat" is the time it takes to heat the mains. In an outdoor reset system, that time doesn't count towards the heating cycle time because you're just heating the mains, not the living space. Shortening the overall time between cycles reduces the preheat time because the boiler and piping are still hot.

Me too!

@ December 11, 2013 9:53 PM in Running 2 CPH finally and loving it!

I've been running > 1 CPH since the weekend before Thanksgiving. It's really reduced the temperature swings versus 1 CPH. Today at a setpoint of 68 degF the temperature range was 67.8 to 68.4.

I currently have the heating cycle set at 20 minutes, which would be 3 CPH except that it doesn't include preheat which today ranged from just under 2 minutes to 5:15. The outdoor reset/heat loss algorithm calculated "heat on" times between 3:16 and 9:50, or 16% to 50% of the cycle time.

I'm going to leave it like this at least for the rest of the month, and then look at the btu per degree data numbers to see if it uses more fuel than 1 CPH. Gut feel right now says no, but even if it's slightly higher the perceived comfort is worth it.

Pressure Control

@ December 8, 2013 8:29 AM in ultra low pressure ARCO system maintained at higher pressure

The transmitter is off the shelf, but the control is not. Won't help this boiler unless the burner modulates.

A few years back I developed a much less complicated control to better manage end-of-cycle short cycling for single-stage on-off burners, using a time-delay relay and a vaporstat. There's a schematic around the middle of this thread in the post titled "Adding a Time Delay to Vaporstat Cut-In".


@ December 7, 2013 9:35 PM in Another Twin System - 6" Drop Header

Have the modulating control fixed the short cycling you were experiencing on the 2nd boiler?

I think you win the "tallest riser" contest

@ December 4, 2013 8:30 PM in An Epic Tale: I hear the Trane a comin'!

Wet steam has no chance against those risers. Wow!

More! More!

@ December 4, 2013 8:28 PM in An Epic Tale: I hear the Trane a comin'!

There's beauty in the process too, Colleen, so keep those install pics and commentary coming.

And besides, isn't HH everyone's personal blog? :-)


@ December 4, 2013 5:50 PM in Steam Pro in Philadelphia PA

Call JStar. He'll do right by you and your system.

Steam Arrival (Preheat) Timing

@ December 4, 2013 11:23 AM in Got an estimate

Here are typical times on my one-pipe system from a cold start in mins:secs. The distance from where steam enters the main to the preheat sensor is 38 feet. Other factors to consider are that this system is well-vented and preheat pressure is one ounce per square inch or less.

--> Burner On to Header Hot: 07:00
--> Header Hot to Main Hot: 02:30
--> Main Hot to Preheat Sensor Hot: 02:45
--> Total Preheat Time: 12:15

Trend Charts

@ December 1, 2013 2:45 PM in Midco Low-Nox Burner Performance Report

I don't have a sensor in direct contact with the boiler water, but I do have one in the aquastat thermowell on the tankless coil that's pretty close.

Here are several trend charts showing 1) Long heat cycles from 11/20, 2) Short heat cycles from 11/30, 3) Focus on setback recovery from #2, and 4) Focus on maintaining temperature from #2. In #3, you can see how the heat loss algorithm reduces the on time as the indoor temperature approaches setpoint.

I used a program called DatPlot to produce these charts. It has a lot of nice features, especially for a free package. You can download it at


@ December 1, 2013 1:03 PM in Midco Low-Nox Burner Performance Report

Maybe I'm mis-using the term. In my system, there's a differential and an anticipator value. The differential is the amount below temperature setpoint that will start a heat cycle. The anticipator is the amount below temperature setpoint that will shut off the burner ("anticipating" that the temperature will coast to or past setpoint). I usually keep them within 0.1 or 0.2 of each other.

Physical improvements

@ December 1, 2013 12:56 PM in Midco Low-Nox Burner Performance Report

Hi Rod - Two things might help: insulating the returns and bringing in outside air for combustion.

I have almost 100 feet of return piping, some of which is behind a false wall, not to mention that much 1-1/4" insulation is around $200. Unless someone has some hard data, I don't see the return on investment.

Outside combustion air is probably the better bet, since it should decrease stack temps and increase efficiency, which in turn might cut preheat times. To do it right I need to break through two 1-foot thick stone walls. I might try rigging something temporary through a window to test it, but that's still almost 25 feet from the burner. Plus I wouldn't be able to tell anything without a combustion analyzer, so I'd need to wait until JStar was in the area again, unless I can locate the one that our combustion controls group at work is rumored to have.

One operational change that is having a big impact on preheat times is an experiment I'm currently running where the heating cycle times are reduced 50-66 percent (roughly 2-3 CPH). A nice side effect of this is that the pipes are still hot when the next cycle starts, so preheat times are down to just a couple of minutes. The sample size is still too small to draw any conclusions about fuel economy, but once I have more data I'll post a report.
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