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Joined on November 14, 2009

Last Post on July 16, 2014

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Midco specs

@ April 8, 2013 6:36 PM in A Steam Odyssey: Midco Low-NOx Burner Oil to Gas Conversion Project

The LNB-500 is rated 100 to 500 MBH. The LNB-1000 is 150 to 1000 MBH. In both cases, the burner is modulated with a 2 to 10 volt dc signal.


@ April 8, 2013 5:56 AM in A Steam Odyssey: Midco Low-NOx Burner Oil to Gas Conversion Project

It's the 120 vac unit. The probe has never been used; the CycleGard & Safgard use the same probe so I left the CycleGard probe in the boiler when I put the Safgard in.

I'm really excited about this project (and I think JStar is too!). Looking forward to seeing how the Midco performs.

Pressure reset control

@ April 7, 2013 8:37 PM in A Steam Odyssey: Midco Low-NOx Burner Oil to Gas Conversion Project

Hadn't considered a pressure reset control scheme, Dave, but I would be very interested in learning more about it. I have a variety of sensors on and off the boiler, and built a lot of flexibility into the controls in order to be able to try out new ideas like this. Not quite "plug-and-play", but if a control strategy uses the sensors I've got, it's a fairly simple matter to add it to the system. PM me if you'd like to discuss further.

Interesting idea

@ April 7, 2013 1:42 PM in A Steam Odyssey: Midco Low-NOx Burner Oil to Gas Conversion Project

Would you place such a sensor in the water/air space in the boiler or on the casting? If the boiler was firing and there was a low water condition but there was still water in the boiler, I wonder what the air temperature would be. I'd think you'd see a measurable change in the casting temp if it was dry firing. Either case, I'm not real keen on dry firing the boiler to test it out :-)

My boiler has a Hydrolevel Safegard-450 LWCO. It came with a CycleGard but I hated the intermittent level test "feature" so I replaced it (anybody want a gently used CycleGard?). Both of those use a conductivity probe, I believe. At any rate, it works well.

It's probably worth noting that nothing I've done will replace or impede the safety limit controls already on the boiler - the pressuretrol and LWCO.


@ April 7, 2013 12:57 PM in A Steam Odyssey: Midco Low-NOx Burner Oil to Gas Conversion Project

responds much more rapidly to changes in input than temperature, I've found. Also, the fact that the water in the boiler is boiling doesn't tell you what's happening out in the rest of the system. Could be pre-heating the mains, could be halfway through a heat cycle. On this system the boiling point versus pressure is negligible as I'm running at less than 2 ounces of pressure. Might be different if you were running at 1 PSI, there you're looking at a 3 degree difference, but I still think it would be hard to control to that.

For ideal pressure control you'd probably want a pressure transmitter at the end of the mains, but I have four of those and even cheap pressure transmitters aren't cheap. The single one on the boiler seems to work OK; I can look at a pressure trend from my system and tell you within +/- one minute of when steam gets to the farthest radiator.

Safety: I'm working on a series of posts describing the control system in detail, but for now I'll say that the system is set up to fail over to wall thermostat control in the event of a power failure, program crash, or computer failure.

A Steam Odyssey: Midco Low-NOx Burner Oil to Gas Conversion Project

@ April 7, 2013 11:34 AM in A Steam Odyssey: Midco Low-NOx Burner Oil to Gas Conversion Project

Following a series of technical email exchanges with Charlie Aiello at Midco International, I took the plunge and ordered their LNB-500 low-NOx modulating gas burner to replace the oil burner on my Utica Starfire steamer.

Joe Starosielec (JStar) from ecuacool was out to the house in March to scope out the job. In addition to the conversion, Joe will also be de-knuckleheading the near-boiler piping that the oil company installers put in when the boiler was replaced back in 2009, putting in a nice new 3" drop header, and fixing a few other off-boiler piping issues.

The burner will modulate based on steam pressure in the boiler, with an override control on low stack temperature. I've spent the last several months re-writing the boiler control software that I described here back in November to run in firmware on a single-board computer, and to add new modulating control algorithms for the steam pressure and stack temperature. In March I finished the wiring and continuity checks for the new controls box, and the unit is now in bench testing with simulated sensors.

The burner is scheduled to arrive on Monday; the conversion will be done over two days on April 17th & 18th. I'll post pictures and updates as the project progresses.

Want 1

@ April 4, 2013 9:38 PM in 4" Drop Headers make us giggle

I can haz drop header plz?

Musical Instrument Acquisition Disorder

@ March 19, 2013 11:31 AM in I've always found better musicians here!

If there's a name for what I've got, that's it. Been playing a variety of somewhat obscure instruments for 25 years or so (though none to anything even approaching a professional level), including hammered and mountain dulcimers, anglo concertina, mandolin, pennywhistle, Swedish nyckelharpa and sackpipa, and a variety of bellows-blown bagpipes - Northumbrian, Scottish, Border, Irish Uilleann. I help run The Pipers' Gathering which is the largest annual convention in North America for bellows-pipes enthusiasts.

Just sent you...

@ March 5, 2013 9:00 PM in Midco lonox burner availability

... an email through the forum.



@ February 1, 2013 7:41 PM in New Boiler at the Best Mansion

Thanks, Dave. I appreciate your taking the time to do this. I'm always interested in getting empirical data from other systems to supplement what I'm learning from my own. This will no doubt keep me busy for a while; I'm not up on vapor vacuum systems so it's time to crack open the Lost Art book again.

I had a look at your website for the mansion. What a great building and history! Fantastic that the 1928 conversion was done with such care, and how well it's been maintained over the years.

Cycle times

@ January 30, 2013 8:29 PM in New Boiler at the Best Mansion

Thanks Dave, that's the information I was interested in. I take it you're not running the setback/recovery program on the Tekmar, those would be affected too. Sounds like you've got it dialed in just about perfect. I'm curious what sort of cycle times you're running for preheat, heat on, heat off.

Overrides & Tekmar

@ January 30, 2013 8:44 AM in New Boiler at the Best Mansion

Does running in either of the override positions have any effect on the adaptive algorithms in the Tekmar control?

What's the purpose

@ January 30, 2013 7:07 AM in New Boiler at the Best Mansion

of the High / Low / Auto switch?

Dew Point

@ January 28, 2013 2:06 PM in Calculating flue gas condensing temperature

Thanks SWEI. I found a dew point chart on that indicates dew points for natural gas between 140 and 128 degF for excess air between 0% and 50%.

Are these absolute temperatures, or are they relative to the ambient temperature?

Calculating flue gas condensing temperature

@ January 28, 2013 1:03 PM in Calculating flue gas condensing temperature

In the spring I'm having JStar replace the oil burner on my steamer with a Midco Low-NOX modulating gas burner. Charlie from Midco informs me that they haven't yet determined the actual low fire DC signal required to avoid condensing in the flue.

My boiler control measures stack temperature via a thermocouple in the flue about 3 feet from the boiler. Current operating temperature is about 470 degF.

Is there a way to calculate the condensing temperature? If so, I can design the modulating control with a low limit during turndowns based on the stack temperature.

I wrote to Nest

@ January 15, 2013 1:37 PM in You Can't Set Cycles per Hour on a Nest Thermostat

a while back asking them to compare and contrast their True Radiant controls with an outdoor reset control. The Nest Support person who replied basically said they didn't know anything about outdoor reset systems and then launched into a marketing blurb about how awesome True Radiant is. Really? They couldn't go ask someone in engineering or product development? As much as I like Apple products (the prez of Nest used to work for Apple) the thing that bugs me most is the "you don't need to know what's under the hood" attitude.

This sounds similar

@ December 31, 2012 3:21 PM in New steam control principle

to what I've been working on with my own control. I fetch the wind chill temperature over the internet from a local WeatherBug station, and if it's lower than either of the two outdoor temperature sensors, I use the WeatherBug temperature in the outdoor reset calculations. I've been running a heat loss replacement model for a while now, and find it more accurate than the time-proportional model in calculating the run time. I've recently implemented an anticipator, and while it's not yet smart enough to react to outdoor temperature in the way Dave describes, it's helped keep the indoor temperature swings to 1 degF or less.


@ 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.
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