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Joined on November 14, 2009

Last Post on August 29, 2014

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@ December 6, 2012 9:47 AM in Aquasmart, ODR with steam?.

Hi Colleen,

Let me start by saying that I'm a homeowner, not a pro. From what I can tell, the AquaSmart control is only for hot water boilers, not steam. The AquaSmart works by adjusting the boiler water temperature, and we can't do that with a steam system because if the water isn't boiling, it isn't making steam.

The Tekmar 279 control works by adjusting the length of time that the boiler runs based on the outdoor temperature. Unfortunately, it is only a single-stage (on/off) control and won't directly control a modulating burner. Honeywell makes a "modulating pressuretrol" that might work with the Tekmar, but I don't have any experience with it and will defer to a pro's recommendation. There's a thread here about how it works.

Something else to consider is the Pajek Pressure Controller, which is a high/low fire system and was originally developed for a vapor system. Contact Gerry Gill for more details.

The ODR system I'm using is of my own design (I do industrial process controls for a living) but it's very experimental and not something I'd be comfortable installing in someone else's house at this point. There's way more information than you wanted to know at the link in my signature line. I'm looking at converting from oil to a modulating gas burner in the spring, so I'd be very interested to hear what unit the Midco folks recommend to you.



@ December 5, 2012 9:12 PM in A Steam Enthusiast's Outdoor Reset Control

Thanks, Dave. I spent a lot of time studying the commercial units before deciding to embark on this project. The two big shortcomings for me were the lack of pressure short-cycle management and historical data logging capability.

On the Tekmar, if you increased the cycle time wouldn't the boiler ON time also increase for the same spot on the heating curve? I see what you're getting at though. If you also adjusted another parameter, maybe reducing the boiler design percent, you could raise the cycle time without increasing the ON time for that point on the curve.

Like you, I saw some pretty short calculated cycle times on my own system. That really bugged me because from a completely cold start my steam established time is around 15 minutes, 5 to 10 if the boiler is still warm, and that's an awful lot of fuel for preheating if the cycle is less than 5 minutes. I got around it some by lowering the WWSD temperature. I like your idea of checking the calculated cycle time before firing the boiler; mind if I borrow it?

Which Midco?

@ December 5, 2012 4:26 PM in Aquasmart, ODR with steam?.

On a non-modulating steam boiler, ODR works by changing the length of time the burner runs (and thus the amount of steam produced) based on the outside temperature. The Heat-Timer site has a general overview, while the Sequence of Operations section of the Tekmar 279 manual goes into more detail.


Which Midco burner are you looking at for your conversion?

Pressure transmitter

@ December 4, 2012 10:36 PM in A Steam Enthusiast's Outdoor Reset Control

Hi Tim,

I used an SSI Technologies model P51-3-G-UC-I36-20MA-R. You can get one from DigiKey here.

As a lower cost alternative, Phidgets now has a series of differential gas pressure sensors, including a 3.6 PSI model (1126_0) that plugs right into the Phidget Interface Kit. No need for a separate 4-20ma converter board. If they'd offered this two years ago I would have bought one instead of the pressure transmitter/converter combination. The only concern I'd have is the max operating temperature is only 185 degF. While you shouldn't see anywhere near that temperature as long as there's water in the pigtail, direct contact with steam would probably fry it.

The code generates the dashboard, faceplates, and all other displays. The gauges on the dashboard are an open source package called SpeedyHMI that's available for free download on

Phidgets is a great platform for experimenting, and it supports many, many languages inlcuding C++. The first pass of my code was for data acquisition and recording; once that and the user interface were in place it wasn't that much more work to do the actual boiler control (except for the testing part. Lots of testing).

Good luck!

Thermal calcs

@ December 1, 2012 11:08 AM in A Steam Enthusiast's Outdoor Reset Control

I didn't do the thermodynamic math to quite that level, George.

The heat capacity of the radiators is calculated using Equivalent Direct Radiation. We know that one square foot of EDR can liberate 240 btu per hour, so that value multiplied by the total EDR of the radiators (which you can calculate from the chart referenced in this thread) gives you the total heat capacity in btu/H.

In my case, the total EDR is 607 (from the system diagram in my second post above) which yields a total radiator heat capacity of 145.6 MBtu/H

We get the net I=B=R heat capacity rating of the boiler from the manufacturer's specs. Mine's 152 MBtu/H, so the boiler is reasonably well matched to the load.

I used the Slant/Fin HeatLoss Explorer 2 software (available here for Windows and here for iPhone/iPad) to calculate the building heat loss. It takes into account the heat capacity and thermal conductivity of the components (walls, doors, windows, roof, etc) of the building envelope, and returns the heat loss of the building in MBth/H at the outdoor design temperature.

The heat loss coefficient of the building is then calculated as Q = UA / (Tin - Tout), where:
  1. Q = heat loss coefficient in Mbtu/H/degF
  2. UA = heat loss in MBtu/H
  3. Tin = indoor design temperature
  4. Tout = outdoor design temperature
Mine is UA=133 Tin=67 Tout=10, resulting in a coefficient of 1.51 MBtu/H/degF.

There's a very good article here by John Sigenthaler where he discusses the mathematics of reset control. While it specifically addresses hot water heating, most of the principles are applicable to steam.

Good news

@ November 24, 2012 4:53 PM in Columbia Joins the Wet-Base Power-Gas Steamer Ranks

Good to know that the Utica Starfire can take a power gas burner. If it turns out the Midco radial burner isn't a fit for my own Starfire, I'll at least be able to have a Carlin installed in the spring.

I'd be looking at a 275 MBtuH top end firing rate. What else do you take into consideration when selecting one of these units? Is there any particular advantage of the 50-275 MBtuH unit over the 150-275 MBthH?

duplicate post

@ November 22, 2012 6:57 PM in A Steam Enthusiast's Outdoor Reset Control

duplicate post deleted

Making the leap

@ November 22, 2012 6:57 PM in A Steam Enthusiast's Outdoor Reset Control

If that's the only thing holding you back from going to a Tekmar, Rod, all you may need is maybe $10 worth of parts and some spare time.

You could get yourself a DPDT (double-pole, double-throw) switch and a mounting box, and find a place to mount it where your wife can find it. Find the terminals on the boiler where the thermostat wires attach. Disconnect the thermostat wires, and run a new pair of wires from the boiler terminals to the center terminals on the switch. Connect the thermostat wires to one of the end pair of terminals on the switch, and wire your new control to the remaining pair. Finally, label the switch positions, and you'll have a quick and easy way to switch between your new advanced control and the thermostat backup.

I never expose http ports

@ November 21, 2012 2:02 PM in A Steam Enthusiast's Outdoor Reset Control

for just that reason. Everything sits behind a VPN. And because this is still in the experimental stages, I have safeguards in place outside of the software to prevent a runaway.

It's written in

@ November 21, 2012 10:42 AM in A Steam Enthusiast's Outdoor Reset Control

VB.NET. The code runs on a laptop that's dedicated to home automation (it also runs the lighting controls). The Phidgets I/O boards take care of the low-level sensor management and data acquisition.

Not ready for prime time

@ November 21, 2012 10:41 AM in A Steam Enthusiast's Outdoor Reset Control

It's nowhere near ready for prime time, Frank. Think of it more as a prototype. To make it marketable, it really needs to run in firmware instead of on a laptop.


@ November 21, 2012 8:24 AM in A Steam Enthusiast's Outdoor Reset Control

Insteon is similar. Crestron sells through a dealer network, so you need to hire an installation firm to set up the system. Insteon is geared more towards the do-it-yourself market.

I use a software package called Home Control Assistant to coordinate the lighting controls (


BMC Hardware and Software Platform

@ November 20, 2012 3:43 PM in A Steam Enthusiast's Outdoor Reset Control

Computer Hardware and Software

BMC was written in Visual Basic .NET and runs on a repurposed Dell laptop under Windows XP. This computer is dedicated solely for home automation – it runs the boiler control as well as the INSTEON lighting automation system for the house. Sensors on the boiler and elsewhere are connected to the PC using Phidgets USB-based I/O. Phidgets (“physical widgets”) are a set of ‘plug-and-play’building blocks for low cost USB sensing and control from a PC. For more info on Phidgets visit their website at

USB I/O Interfaces

BMC uses two Phidgets USB I/O interfaces:
  1. Model 1018 Interface Kit 8/8/8. The interface kit allows you to connect devices to any of 8 analog inputs (0-5 volts), 8 dry-contact digital inputs and 8 digital outputs. It provides a generic way to interface a PC with various devices.
  2. Model 1051 single-input temperature sensor. This module supports one type J, K, E, or T thermocouple.
Analog Sensors

There are nine analog input sensors:
  1. (2) indoor temperature sensors
  2. (2) outdoor temperature sensors
  3. (1) un-tempered DHW and (1) tempered DHW temperature sensor
  4. (1) condensate return temperature sensor
  5. (1) low pressure sensor
  6. (1) K-type thermocouple for stack temperature
For the indoor and outdoor temperature sensors, one is a Phidgets 1124 Precision Temperature Sensor and the other is a 10K ohm thermistor. Sensor selection for each pair can be configured as Sensor 1, Sensor 2, First Good, Lowest, Highest, or Average.

The boiler provides domestic hot water through a tankless coil. Two 10K thermistors provide readings for un-tempered and tempered DHW. The un-tempered DHW thermistor shares the thermowell with the aquastat probe. The Tempered DHW thermistor is mounted upstream of the cold water mixing valve.

Another 10K thermistor is secured to the base of the riser at the furthest radiator. This is the Condensate Return sensor and is used to determine when the mains have filled with steam.
Steam pressure is measured with a 4-20ma, 0-3 psi pressure transmitter. It is attached to the Phidgets interface via a Phidgets 1132 4-20ma converter board.

Stack temperature is measured with a type-K thermocouple, inserted in the stovepipe about four feet from the boiler. Operating temperatures are typically around 460 degF.

Digital Inputs

Thermal switches that trip at 180 degF are installed on the boiler header and at the entrance to the steam main. These were used for time trials to see how long it took for the header and main to get hot after the burner went on, and to cool when off.

A McDonnell-Miller flow switch is installed in the DHW supply line. This allows on-demand (with a 3 to 4 minute heatup delay) hot water during periods when the DHW schedule is in OFF mode., by detecting hot water flow.

In 2011 a major remodel was done on the house, part of which included replacing all of the old knob-and-tube wiring. INSTEON lighting controls were installed throughout the house. INSTEON keypad light switches have On and Off buttons for the lighting load, plus four additional buttons that can be programmed to talk to other INSTEON devices in other rooms. One of the keypad buttons in the kitchen and bathroom was assigned as a “Call for DHW”; when pressed these buttons activate an INSTEON IOLinc module, which closes a dry contact wired to a Phidgets digital input in parallel with the flow switch.

Digital Outputs

All of this controls two relay outputs. The first is a “mode” relay. When BMC is off, the mode relay is de-energized and is wired to allow the wall thermostat and aquastat to run the boiler. When BMC is active and in Outdoor Reset mode, the relay is energized, removing control from the wall thermostat. A second relay then controls the burner.
An “Emergency Stop” button on the main display will immediately take BMC off control by de-energizing the burner relay output and keeping it off until the E-Stop button is deactivated.

Faceplate and Detail Displays

Clicking on a gauge or discrete tag on the main display will call up a faceplate for the associated sensor. The faceplate and detail displays show the sensor values, alarm status, control limit/setpoint configuration and raw Phidgets sensor data.

Data Logging with BMC

@ November 20, 2012 3:42 PM in A Steam Enthusiast's Outdoor Reset Control

Event Log

BMC saves data to an event log whenever a system event occurs, such as transitioning from one state to another (Idle to Preheat, for instance). Depending on the event, BMC may store several lines of event data. For instance, when transitioning from Idle to Preheat, it logs the event change, current outdoor/indoor/comfort setpoint temperatures, burner status, and thelength of time the boiler has been off since the last heating cycle.

Continuous History Log

BMC saves analog and discrete data values to a continuous history log whenever one of the analog inputs or digital input values changes beyond a configured change threshold. This data is stored in .csv format, and is used by the graphing application to produce a trend chart.

I've used the open source package “LiveGraph” to display trend charts from the .csv file data. LiveGraph is available for free download at:

The attached graph shows trends for the following analog inputs:
- Outdoor temperatures are blue
- Indoor temperatures are green
- Condensate temperature is yellow
- Tempered and untempered DHW are red
- Steam Pressure is purple, and is scaled by a factor of 100 for display

Outdoor Reset Modeling with BMC

@ November 20, 2012 3:42 PM in A Steam Enthusiast's Outdoor Reset Control

BMC supports two outdoor reset mathematical models; time-proportional and heat loss. Each model calculates the number of minutes that the boiler needs to be ON during the heating cycle. The model is calculated when the boiler transitions from the Preheat state to the Heat Cycle ON state. The “active” model that is used for control is selectable from the Outdoor Reset Model display.

Time Proportional Model

The time-proportional model uses the relationship between the current outdoor temperature and the configured indoor and outdoor design temperatures to calculate the boiler’s “On” time during a heating cycle. This method is commonly used in the commercially available outdoor reset control systems.

Heat Loss Model

The heat loss model uses the building’s calculated heat loss (in MBtu per hour) and the boiler’s net MBtuH rating, along with the indoor and outdoor design temperatures, to calculate the boiler’s “On” time during a heating cycle. The heat loss model also employs a setback recovery feature that adds a setback “boost” to the calculated “On” time when the current temperature is below the comfort setpoint by a configurable amount.

Model Equations and Boiler Operating States

The forum software doesn't support tables, so I'm providing the Outdoor Reset Model equations and boiler operating states as image attachements.

Temperature Setback and DHW Scheduling with BMC

@ November 20, 2012 3:40 PM in A Steam Enthusiast's Outdoor Reset Control

Temperature Setback

BMC includes 7-day 4-period-per-day temperature setback scheduling, as is typical on many thermostats.

Domestic Hot Water Scheduling

The boiler supplies domestic hot water through a tankless coil. The old boiler and aquastat would keep the DHW temperature between 110 and 140 degF during the warm weather season. It burned on average 150 gallons of oil each season to do so. DHW scheduling was added to BMC so that water is only heated during scheduled demand periods – in the morning for bathing and evening for dishwashing, for instance.
Domestic Hot Water production can be configured to run in several modes:
  1. On a programmable on a 7-day, 4-period-per-day time schedule,
  2. Delayed On-demand (see discussion below)
  3. Using hi/lo setpoint control based either on temperature sensor or the aquastat
  4. It can be turned off entirely for extended away periods
A “delayed on-demand” feature detects hot water flow during off-schedule periods, and if there is flow for a predetermined time (10 seconds), BMC will run a DHW heating cycle. DHW can be available in as little as three minutes from a cold start.

Two means are provided for on-demand hot water. The first is a McDonnell-Miller FS-1 flow switch installed in the DHW supply line on the inlet side of the tankless coil. In addition to the flow switch, Insteon lighting control keypads in the kitchen and bathroom have a dedicated button that wirelessly activates a “Call for DHW” contact closure.

BMC’s DHW scheduling was active for the warm weather season last year, and oil consumption was reduced almost 50%, from 150 gallons to 78 gallons from April through September 2011.

BMC Features (continued)

@ November 20, 2012 3:40 PM in A Steam Enthusiast's Outdoor Reset Control

Data Acquisition

BMC’s data comes from nine analog and four digital input signals:
  1. (2) indoor temperature sensors
  2. (2) outdoor temperature sensors
  3. (1) un-tempered and (1) tempered DHW temperature sensor
  4. (1) condensate return temperature sensor
  5. (1) 0-3 psi pressure transmitter
  6. (1) K-type thermocouple for vent stack temperature
  7. (1) thermal switch on the boiler header
  8. (1) thermal switch on the steam main
  9. (1) flow switch in the domestic hot water supply line
  10. (1) Insteon I/O Linc wireless relay
Dual Temperature Sensor Selection

Redundant temperature sensors are provided for indoor and outdoor temperatures. Sensor selection for each pair of indoor and outdoor temperatures can be configured as Sensor 1, Sensor 2, First Good, Lowest, Highest, or Average. If one of the sensors goes bad (either high or low scale), the system will automatically switch to First Good. If both sensors are bad, the system will automatically go off-line and return control to the thermostat.

Eliminating Pressure Short Cycling

Steam pressure is measured with a 0-3 psi, 4-20 ma pressure transmitter at the boiler. (Point of interest: the pressure transmitter was less than half the cost of a Vaporstat) Normal operating pressure of this system is 1.5 ounces per square inch, with the high pressure trip point set at 2.5 ounces. If the trip point is reached, the burner will shut off and the system will enter a “Pressure Lockout” mode until the condensate return temperature drops below a preset value. This allows the pressure to subside, and eliminates short cycling while allowing the heat already in the system to radiate into the living space. If there is still a call for heat after the lockout temperature is reached, the burner will restart. In practice, high pressure is usually seen towards the end of the heating cycle, and the comfort setpoint is often achieved during the lockout period.

I've attached a photo of the pressure controls on the boiler. I teed two pigtails to the single port on the boiler; one for the pressuretrol and 0-30 psi gauge, and another for the vaporstat, 0-3 psi gauge, and 0-3 psi pressure transmitter. The latter pigtail has a shutoff valve for blowdowns, and a calibration port to allow the vaporstat or pressure transmitter to be calibrated in place. The vaporstat is currently out of service; it was used along with a time-delay relay in an earlier pressure lockout control scheme.

Use of Wind Chill as Outdoor Temperature

BMC can optionally fetch the current wind-chill (or “feels-like”) temperature over the Internet, from a nearby weather station. If the wind chill temperature is less than the temperature from the outdoor sensors, BMC will use the wind chill value in the outdoor reset calculations.

Web-Accessible Thermostat Display

A simplified thermostat-like display can be accessed from a web browser.

BMC Environment & Features

@ November 20, 2012 3:39 PM in A Steam Enthusiast's Outdoor Reset Control

The house is of four course brick construction, and has approximately 3100 sq ft of living space plus an attic and an unfinished basement. All of the windows on the first and second floors were recently upgraded with low-e glass replacement windows. The remaining windows are double-pane glass and were replaced by the previous owner about 20 years ago. The majority of the walls are uninsulated save for a 2” air gap between the brick and wall. The third floor and attic spaces are fully insulated. Using the Slant-Fin HeatLoss Explorer software, I calculated the building’s heat loss at 133 MBtuH at an outdoor design temperature of 10 degF.

The boiler is a Utica Starfire SFE-5175S oil-fired unit, rated at 152 MBtu/hr of steam, or 633 sq. ft. EDR, with a tankless coil for domestic hot water. The EDR of the connected radiation is 607 square feet, making the boiler about 4% over-sized. After fine-tuning the system, it heats the building with only 1.5 ounces of steam pressure.

Boiler Monitoring & Control Features

BMC’s features include:
  1. Outdoor Reset Control using either time-proportional or heat loss mathematical models.
  2. Redundant indoor and outdoor temperature sensors, with configurable sensor selection (High/Low/Average/First Good).
  3. Automatic switchover to a good sensor if one of the indoor or outdoor sensors fails.
  4. Optionally retrieves current local wind-chill temperature over the Internet, and uses it as the outdoor temperature in outdoor reset calculations.
  5. Eliminates short-cycling on pressure by entering a pressure lockout mode when the adjustable high pressure limit is reached.
  6. 7 day, 4 period-per-day temperature setback scheduling.
  7. 7 day, 4 period-per-day Domestic Hot Water heating schedule.
  8. A web-accessible thermostat-style display
  9. On-demand DHW by pushbutton or when hot water flow is detected.
  10. Highly configurable – many parameters can be adjusted to tune the system to its environment.
  11. Logging of continuous analog data and heating cycle events, with trend charting for analog data.
  12. Automatically reverts to wall thermostat control in the event of a critical failure.

A Steam Enthusiast's Outdoor Reset Control

@ November 20, 2012 3:37 PM in A Steam Enthusiast's Outdoor Reset Control

I live in an 1890’s three-story brick home in south-eastern Pennsylvania with a one-pipe steam heating system. The boiler was replaced in 2009, and after fine-tuning and balancing the rest of the heating system (insulating the mains, re-sizing and replacing vents on the steam mains and radiators using the Gill & Pajek vent capacity charts), I began looking at other ways to reduce fuel consumption. An outdoor reset control was at the top of the list. The commercially available outdoor reset controls all lacked specific features I wanted, so with a background in industrial process control I decided to develop my own control, which I’ve dubbed "BMC" for Boiler Monitoring & Control.

This has been a work-in-progress since 2010. The first iteration was a time delay relay to control end-of-cycle short cycling on pressure. This was followed by a clock timer/relay control to schedule production of domestic hot water. For the third iteration, I purchased sensors and wrote some software to do data acquisition and charting of temperatures and pressure at the tail end of the 2010 heating season. The current iteration incorporates the mechanical controls into the software and adds outdoor reset modeling. I've had the software in control of the boiler since January 2012, with some fine-tuning along the way.

Before I get started, I'd like to take this opportunity to thank Dan Holohan and all the contributors here at for sharing their knowledge and expertise over the years. Thanks guys!


Looks interesting

@ September 20, 2012 11:32 AM in Midco Radial Burner

I've already prepaid my oil for this year (ouch!), but come spring I'll be taking a closer look at this unit.

I wonder if this burner could be modulated using steam pressure. Seems to me that given an otherwise well-tuned steam system, the objective would be to first fill the mains on high fire, then turn down to maintain an optimal system pressure. You'd need some way to de-bounce the pressure signal, especially if the operating pressure is very low. I have a 4-20ma, 0-3 PSI pressure transmitter on the gauge pigtail (which I'm currently using with my home-grown outdoor reset control) that would be perfect for this application.

1st-generation Starfire?

@ August 19, 2012 7:26 AM in Utica Starfire 3 steam boiler- oil burner conversion to gas burner

Bill, how do you distinguish a first-generation Starfire, and how is it better than a later model? Mine was installed in 2009 and, like Helm, I'm thinking about a gas power burner conversion.

I thought the worst part

@ May 19, 2012 5:47 PM in Is this why we make fun of engineers

was when the author wrote, "Steam heat is wasteful". Steam heat is wonderful, poor maintenance is wasteful.
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