How many

Tinman

of your steam boiler replacements are you guys installing a second control, vaporstat or high limit, and a lower scale pressure gauge? I haven't done either yet but seems like it should be done in most cases? If you're running at less than .5, its really hard to guess where you're at with a 30 psi gauge. I'm guessing this has already been discussed many time???

Abracadabra

Every install. 2 pressuretrols and a vaporstat along with a 0-20 oz gauge.

Tinman

Thanks Tom. Where are you getting the 20 oz gauges?

EzzyT

@Stephen Minnich I get my 0-3 psi gauges on Amazon

Tinman

Thanks EzzyT

Paul S_3

@Stephen Minnich http://www.valworx.com/product/low-pressure-gauge-25-0-3-psi ......i get them from here they come pretty quick...

ChrisJ

If you want lower pressure gauges for your installs I'd recommend checking Ebay and other places for Dwyer. I like them more than the Wika and they offer more options.

They even have ones that show vacuum
For example, I have a -8" to +16" gauge model LPG4-D9122N.

0-10" LPG4-D8022N
0-15" LPG4-D8122N
0-25" LPG4-D8222N 14.4 ounces full scale
0-40" LPG4-D8322N - almost 1.5 PSI full scale.
-24" - +40" LPG4-D9322N

Some guys may prefer ounces, or PSI but I got used to inches of water.

Amazon has them, from time to time you'll find them on Ebay and Dwyer themselves sells them.

https://www.dwyer-inst.com/Product/Pressure/SinglePressure/Gages-Dial/SeriesLPG4


That said, I agree with @Hatterasguy. Keep the pickup factor lower and forget about the Vaporstat. The system will regulate it self and the Pressuretrol is there just in case.


I switched to Dwyer after talking to @MarkS
Here's a picture of what the series 4 gauges look like, specifically the vacuum \ pressure ones.

PMJ

I don't want to hijack the thread but I think it is important to mention that the real secret weapon in Chris's system that allows this ultra low pressure is the control - which limits run time based on the conditions. Aren't most people stuck with pressure being the only variable that shuts the boiler off so they necessarily must run higher than this just to have something controllable? And once you have shut off at the one pressure available to you you have already put into your system way more steam that is required on the average day for the conditions. This is the very thing that Ecosteam addresses.

This has also been my point all along - that if you spread the running out enough you can maintain full enough radiators for any conditions with no pressure at all and in so doing end up with much more even heat. Coal fired systems for which all this piping was designed spread steam supply out to 100% of the time. Once you make the leap in your thinking to run time as the main control ingredient (as Ecosteam does and I have with my approach ) everything gets much easier and pressures can approach zero.

Abracadabra

@Stephen Minnich I get my gauges from Grainger. I like walking in and picking them up.

PMJ

Hatterasguy said:

PMJ said:

I don't want to hijack the thread but I think it is important to mention that the real secret weapon in Chris's system that allows this ultra low pressure is the control - which limits run time based on the conditions. Aren't most people stuck with pressure being the only variable that shuts the boiler off so they necessarily must run higher than this just to have something controllable? And once you have shut off at the one pressure available to you you have already put into your system way more steam that is required on the average day for the conditions. This is the very thing that Ecosteam addresses.

Most people are stuck with thermostats............

The control assists with the capability to run shorter cycles, if desired. However, Chris' system won't build much pressure even if he runs it continuously for one hour. That's a function of the ratio between boiler net output and EDR.

Get down to between 15 and 20% pickup and piping factor with a proper drop header and a boiler with a 'stat still won't develop any pressure.

This sounds like Chris's Ecosteam sort of isn't needed. Maybe Chris would agree, I don't know. Reading Mark's assessment of why he developed it (which makes perfect sense) he explains it it as more than just more cycles. I think you sell it a bit short with this comment.

However, I do agree that at the end of the day shorter cycles help with many things, including lowering the pressure required to get the job done on any system.

ChrisJ

PMJ said:

Hatterasguy said:

PMJ said:

I don't want to hijack the thread but I think it is important to mention that the real secret weapon in Chris's system that allows this ultra low pressure is the control - which limits run time based on the conditions. Aren't most people stuck with pressure being the only variable that shuts the boiler off so they necessarily must run higher than this just to have something controllable? And once you have shut off at the one pressure available to you you have already put into your system way more steam that is required on the average day for the conditions. This is the very thing that Ecosteam addresses.

Most people are stuck with thermostats............

The control assists with the capability to run shorter cycles, if desired. However, Chris' system won't build much pressure even if he runs it continuously for one hour. That's a function of the ratio between boiler net output and EDR.

Get down to between 15 and 20% pickup and piping factor with a proper drop header and a boiler with a 'stat still won't develop any pressure.

This sounds like Chris's Ecosteam sort of isn't needed. Maybe Chris would agree, I don't know. Reading Mark's assessment of why he developed it (which makes perfect sense) he explains it it as more than just more cycles. I think you sell it a bit short with this comment.

However, I do agree that at the end of the day shorter cycles help with many things, including lowering the pressure required to get the job done on any system.

The entire point of the Ecosteam is to predict how much energy is stored in the cast iron radiators and shut the system down to prevent overshooting.

My temperature usually doesn't swing more than 0.5F total, meaning +- 0.25F. If my setpoint is 72F, I'll expect to see something like 71.75 to 72.25F for example. I can also do a large recovery, say 5-10 degrees and still not overshoot.


The pressure switch set to trip and let the system rest for 10 minutes to dissipate some heat is for oversized boilers, but I have mine set to trip at 1 ounce, just because. It's never tripped yet, even during a 10 degree recovery.

Jamie Hall

"You'll always get temperature overshoot"? How's that again? Not if the thermostat is properly adjusted. It's called anticipation, and it works. Some thermostats (the VisionPro I use) have no actual adjustment, but "learn" the characteristics of the building. Others (the old mercury T87s I use as backups) have adjustable anticipators. The latter, I will admit, do require some care to get right.

And I will also admit that none of them can really compensate properly for recovery from large setbacks.

ChrisJ

Jamie Hall said:

"You'll always get temperature overshoot"? How's that again? Not if the thermostat is properly adjusted. It's called anticipation, and it works. Some thermostats (the VisionPro I use) have no actual adjustment, but "learn" the characteristics of the building. Others (the old mercury T87s I use as backups) have adjustable anticipators. The latter, I will admit, do require some care to get right.

And I will also admit that none of them can really compensate properly for recovery from large setbacks.

There's absolutely no way for any thermostat with anticipation or "learning" to ever work properly. Well, ok, they will for a short time.

Anticipation will only work under one set of conditions, once the heatloss goes up or down it'll be wrong.

Learning works as well until outdoor conditions change. I found this with my VisionPro. By the time it learned and got things right or close to right the conditioned changed totally throwing it off.

I suspect, but don't know for sure, that hot water with cast iron radiation must suffer from the same problem. @Hatterasguy ??

My guess is anyone that has not noticed the problem simply isn't as picky as I am.

My absolute favorite conditions so far in this house are when it's 0 or colder out running 3 CPH. The temperature stays so steady it's unreal even in a drafty house. I suspect this is because the boiler and system are closer matched to the heatloss than usual. I sure wish I had 25,000-30,000 btu/h less worth of radiation.

There's also the rare occasion that it's windy out and the Ecosteam barely keeps up with the heatloss and the Visionpro stays calling for heat non-stop. The temperature literally stays in one spot at least according to multiple thermometers. No change at all. The problem is if I tune for that during normal conditions, it'll drop temp during windy ones but I've been tempted to shave a little off and cut it closer.

This is why I started looking at radiators as filter capacitors. The boiler is strictly an ON\OFF device, but the radiators smooth it out. When something can accurately predict the amount of loss in a building the radiators can totally smooth out the changes, it feels more like a radiant system with ODR. The radiators to an extent stay one temperature even though the boiler is putting out bursts of 212F. When it's 0 out my radiators stay very hot.

ChrisJ

Hatterasguy said:

ChrisJ said:

I suspect, but don't know for sure, that hot water with cast iron radiation must suffer from the same problem. @Hatterasguy ??

I use the Honeywell CT3500. It has some excellent algorithms that sense the overshoot and compensate accordingly. On subsequent cycles, the 'stat will open and close repeatedly as it approaches setpoint (on a recovery).

However, it is limited by the exact issue you mentioned. Once outdoor conditions change, the algorithm also has to change.

My final solution to effect no overshoot is to run with significantly reduced SWT. It's hard to overshoot when the rads are at 135F. It's also very hard to do a recovery.

Can you use a two stage thermostat to increase that when it's 1-2 degrees below setpoint?

I asked Mark if we could do this with the Ecosteam. I've been considering relying on a 2 stage thermostat and getting rid of the indoor temp sensor only because it would neaten up the wall by the thermostat.

ChrisJ

Hatterasguy said:

ChrisJ said:

Hatterasguy said:

ChrisJ said:

I suspect, but don't know for sure, that hot water with cast iron radiation must suffer from the same problem. @Hatterasguy ??

I use the Honeywell CT3500. It has some excellent algorithms that sense the overshoot and compensate accordingly. On subsequent cycles, the 'stat will open and close repeatedly as it approaches setpoint (on a recovery).

However, it is limited by the exact issue you mentioned. Once outdoor conditions change, the algorithm also has to change.

My final solution to effect no overshoot is to run with significantly reduced SWT. It's hard to overshoot when the rads are at 135F. It's also very hard to do a recovery.

Can you use a two stage thermostat to increase that when it's 1-2 degrees below setpoint?

I asked Mark if we could do this with the Ecosteam. I've been considering relying on a 2 stage thermostat and getting rid of the indoor temp sensor only because it would neaten up the wall by the thermostat.

I don't have any way to control the WH with the second stage. It's a fixed output of 57K.

You'd install a two stage gas valve on yours?

No,
The second stage will tell the Ecosteam "I'm behind, add more". Not as good as the indoor temp sensor, but good enough. All it is, is a second dry contact.

Without it anything, it takes hours to do even a small recovery.

ChrisJ

Hatterasguy said:

ChrisJ said:

Hatterasguy said:

ChrisJ said:

Hatterasguy said:

ChrisJ said:

I suspect, but don't know for sure, that hot water with cast iron radiation must suffer from the same problem. @Hatterasguy ??

I use the Honeywell CT3500. It has some excellent algorithms that sense the overshoot and compensate accordingly. On subsequent cycles, the 'stat will open and close repeatedly as it approaches setpoint (on a recovery).

However, it is limited by the exact issue you mentioned. Once outdoor conditions change, the algorithm also has to change.

My final solution to effect no overshoot is to run with significantly reduced SWT. It's hard to overshoot when the rads are at 135F. It's also very hard to do a recovery.

Can you use a two stage thermostat to increase that when it's 1-2 degrees below setpoint?

I asked Mark if we could do this with the Ecosteam. I've been considering relying on a 2 stage thermostat and getting rid of the indoor temp sensor only because it would neaten up the wall by the thermostat.

I don't have any way to control the WH with the second stage. It's a fixed output of 57K.

You'd install a two stage gas valve on yours?

No,
The second stage will tell the Ecosteam "I'm behind, add more". Not as good as the indoor temp sensor, but good enough. All it is, is a second dry contact.

Without it anything, it takes hours to do even a small recovery.

I take it that the Ecosteam doesn't know if you're 1 degree behind room setpoint or four degrees behind room setpoint?

The CT3500 certainly knows.

It does know with the indoor sensor I currently have installed.
In fact, I believe it goes down to the hundredth of a degree I believe. I want to get rid of that sensor tho for cosmetic reasons and just rely on the 2 stage thermostat. It'll be by far "good enough" for me as I never do setbacks.

ChrisJ

Hatterasguy said:

ChrisJ said:

Hatterasguy said:

ChrisJ said:

Hatterasguy said:

ChrisJ said:

Hatterasguy said:

ChrisJ said:

I suspect, but don't know for sure, that hot water with cast iron radiation must suffer from the same problem. @Hatterasguy ??

I use the Honeywell CT3500. It has some excellent algorithms that sense the overshoot and compensate accordingly. On subsequent cycles, the 'stat will open and close repeatedly as it approaches setpoint (on a recovery).

However, it is limited by the exact issue you mentioned. Once outdoor conditions change, the algorithm also has to change.

My final solution to effect no overshoot is to run with significantly reduced SWT. It's hard to overshoot when the rads are at 135F. It's also very hard to do a recovery.

Can you use a two stage thermostat to increase that when it's 1-2 degrees below setpoint?

I asked Mark if we could do this with the Ecosteam. I've been considering relying on a 2 stage thermostat and getting rid of the indoor temp sensor only because it would neaten up the wall by the thermostat.

I don't have any way to control the WH with the second stage. It's a fixed output of 57K.

You'd install a two stage gas valve on yours?

No,
The second stage will tell the Ecosteam "I'm behind, add more". Not as good as the indoor temp sensor, but good enough. All it is, is a second dry contact.

Without it anything, it takes hours to do even a small recovery.

I take it that the Ecosteam doesn't know if you're 1 degree behind room setpoint or four degrees behind room setpoint?

The CT3500 certainly knows.

It does know with the indoor sensor I currently have installed.
In fact, I believe it goes down to the hundredth of a degree I believe. I want to get rid of that sensor tho for cosmetic reasons and just rely on the 2 stage thermostat. It'll be by far "good enough" for me as I never do setbacks.

I see.

If you never do setbacks, the second stage will never close...................

Sure it will.
If the power goes out like it did Saturday morning.

That's the point, it's more than good enough for the rare occurrence where I need to bring the temp back up. Power outages, the fall where I get home and the house is 65 because the heat was off all summer etc.

ChrisJ

Hatterasguy said:

ChrisJ said:

Hatterasguy said:

ChrisJ said:

Hatterasguy said:

ChrisJ said:

Hatterasguy said:

ChrisJ said:

Hatterasguy said:

ChrisJ said:

I suspect, but don't know for sure, that hot water with cast iron radiation must suffer from the same problem. @Hatterasguy ??

I use the Honeywell CT3500. It has some excellent algorithms that sense the overshoot and compensate accordingly. On subsequent cycles, the 'stat will open and close repeatedly as it approaches setpoint (on a recovery).

However, it is limited by the exact issue you mentioned. Once outdoor conditions change, the algorithm also has to change.

My final solution to effect no overshoot is to run with significantly reduced SWT. It's hard to overshoot when the rads are at 135F. It's also very hard to do a recovery.

Can you use a two stage thermostat to increase that when it's 1-2 degrees below setpoint?

I asked Mark if we could do this with the Ecosteam. I've been considering relying on a 2 stage thermostat and getting rid of the indoor temp sensor only because it would neaten up the wall by the thermostat.

I don't have any way to control the WH with the second stage. It's a fixed output of 57K.

You'd install a two stage gas valve on yours?

No,
The second stage will tell the Ecosteam "I'm behind, add more". Not as good as the indoor temp sensor, but good enough. All it is, is a second dry contact.

Without it anything, it takes hours to do even a small recovery.

I take it that the Ecosteam doesn't know if you're 1 degree behind room setpoint or four degrees behind room setpoint?

The CT3500 certainly knows.

It does know with the indoor sensor I currently have installed.
In fact, I believe it goes down to the hundredth of a degree I believe. I want to get rid of that sensor tho for cosmetic reasons and just rely on the 2 stage thermostat. It'll be by far "good enough" for me as I never do setbacks.

I see.

If you never do setbacks, the second stage will never close...................

Sure it will.
If the power goes out like it did Saturday morning.

That's the point, it's more than good enough for the rare occurrence where I need to bring the temp back up. Power outages, the fall where I get home and the house is 65 because the heat was off all summer etc.

OK, well that really does cause a setback, albeit undesired.

Yeah,
It's rare enough I really don't need anything, but I'm getting a 2 stage t-stat for the central air, so why not. Actually I think it's a 3H \ 2C VisionPro 8000 series.

PMJ

Hatterasguy said:

PMJ said:

Hatterasguy said:

PMJ said:

I don't want to hijack the thread but I think it is important to mention that the real secret weapon in Chris's system that allows this ultra low pressure is the control - which limits run time based on the conditions. Aren't most people stuck with pressure being the only variable that shuts the boiler off so they necessarily must run higher than this just to have something controllable? And once you have shut off at the one pressure available to you you have already put into your system way more steam that is required on the average day for the conditions. This is the very thing that Ecosteam addresses.

Most people are stuck with thermostats............

The control assists with the capability to run shorter cycles, if desired. However, Chris' system won't build much pressure even if he runs it continuously for one hour. That's a function of the ratio between boiler net output and EDR.

Get down to between 15 and 20% pickup and piping factor with a proper drop header and a boiler with a 'stat still won't develop any pressure.

This sounds like Chris's Ecosteam sort of isn't needed. Maybe Chris would agree, I don't know. Reading Mark's assessment of why he developed it (which makes perfect sense) he explains it it as more than just more cycles. I think you sell it a bit short with this comment.

However, I do agree that at the end of the day shorter cycles help with many things, including lowering the pressure required to get the job done on any system.

Ecosteam or an equivalent is definitely needed on a steam system. Without it, you'll always get temperature overshoot in the building due to the accumulated energy in the emitters.

The purpose of the unit is not to prevent excessive pressure..............it's to prevent excessive temperature in the living space.

"Ecosteam or equivalent is definitely needed on a steam system" yet 99% or more of residential systems don't have them. And, as you put it ,all it does is provide the ability to have more cycles. Ok, I'm really lost now trying to follow you.

And, since the only way to have excess pressure in a steam system is to have quite full radiators (which are never needed to match the conditions), preventing this is the same thing as preventing excess temperature.

The reality is that most residential steam systems make steam at only one speed - high. And that high speed must be able to fill the radiators or you can't match the heat loss on design day. But on an average day that same speed is way way too high for what is needed. The only way to prevent putting too much steam out in the system on an average day is to limit the run - that is shut off WAY BEFORE any radiators fill. Ecosteam and other controls accomplish this. BECAUSE the radiators don't fill the pressure remains low.

God bless anyone who really wants to reduce his boiler down to one that running flat out for hours that won't ever produce enough steam to fill his rads and produce any pressure. Good luck recovering a house from a power failure from 32 degrees(or lower) on a windy design day with that boiler. I'll gladly buy some extra. At 3 cycles per hour simply by adjusting the on vs off times you can run a very oversized boiler at no pressure and heat the place very evenly with no loss of efficiency. There really is no common sense reason to cut it close.

ChrisJ

PMJ said:

Hatterasguy said:

PMJ said:

Hatterasguy said:

PMJ said:

I don't want to hijack the thread but I think it is important to mention that the real secret weapon in Chris's system that allows this ultra low pressure is the control - which limits run time based on the conditions. Aren't most people stuck with pressure being the only variable that shuts the boiler off so they necessarily must run higher than this just to have something controllable? And once you have shut off at the one pressure available to you you have already put into your system way more steam that is required on the average day for the conditions. This is the very thing that Ecosteam addresses.

Most people are stuck with thermostats............

The control assists with the capability to run shorter cycles, if desired. However, Chris' system won't build much pressure even if he runs it continuously for one hour. That's a function of the ratio between boiler net output and EDR.

Get down to between 15 and 20% pickup and piping factor with a proper drop header and a boiler with a 'stat still won't develop any pressure.

This sounds like Chris's Ecosteam sort of isn't needed. Maybe Chris would agree, I don't know. Reading Mark's assessment of why he developed it (which makes perfect sense) he explains it it as more than just more cycles. I think you sell it a bit short with this comment.

However, I do agree that at the end of the day shorter cycles help with many things, including lowering the pressure required to get the job done on any system.

Ecosteam or an equivalent is definitely needed on a steam system. Without it, you'll always get temperature overshoot in the building due to the accumulated energy in the emitters.

The purpose of the unit is not to prevent excessive pressure..............it's to prevent excessive temperature in the living space.

"Ecosteam or equivalent is definitely needed on a steam system" yet 99% or more of residential systems don't have them. And, as you put it ,all it does is provide the ability to have more cycles. Ok, I'm really lost now trying to follow you.

And, since the only way to have excess pressure in a steam system is to have quite full radiators (which are never needed to match the conditions), preventing this is the same thing as preventing excess temperature.

The reality is that most residential steam systems make steam at only one speed - high. And that high speed must be able to fill the radiators or you can't match the heat loss on design day. But on an average day that same speed is way way too high for what is needed. The only way to prevent putting too much steam out in the system on an average day is to limit the run - that is shut off WAY BEFORE any radiators fill. Ecosteam and other controls accomplish this. BECAUSE the radiators don't fill the pressure remains low.

God bless anyone who really wants to reduce his boiler down to one that running flat out for hours that won't ever produce enough steam to fill his rads and produce any pressure. Good luck recovering a house from a power failure from 32 degrees(or lower) on a windy design day with that boiler. I'll gladly buy some extra. At 3 cycles per hour simply by adjusting the on vs off times you can run a very oversized boiler at no pressure and heat the place very evenly with no loss of efficiency. There really is no common sense reason to cut it close.

Ok,
Once again. NO. I have no idea where this keeps coming from. The Ecosteam can be set to run at 1 cycle per hour if the user wishes. The simplest description I can think of is its a very sophisticated anticipator that uses outdoor temp.

Did you read any of my comments?


Also. as with most steam systems my radiation is 94,000 btu/h vs my heatloss of 72,000 btu/h @ -8F. I have absolutely no problem doing a recovery, ever. It doesn't matter how big your boiler is if the radiation can't dissipate it.

SWEI

ChrisJ said:

This is why I started looking at radiators as filter capacitors. The boiler is strictly an ON\OFF device, but the radiators smooth it out. When something can accurately predict the amount of loss in a building the radiators can totally smooth out the changes, it feels more like a radiant system with ODR. The radiators to an extent stay one temperature even though the boiler is putting out bursts of 212F. When it's 0 out my radiators stay very hot.

Exactly.

PMJ

Ok,
Once again. NO. I have no idea where this keeps coming from. The Ecosteam can be set to run at 1 cycle per hour if the user wishes. The simplest description I can think of is its a very sophisticated anticipator that uses outdoor temp.

Did you read any of my comments?


Also. as with most steam systems my radiation is 94,000 btu/h vs my heatloss of 72,000 btu/h @ -8F. I have absolutely no problem doing a recovery, ever. It doesn't matter how big your boiler is if the radiation can't dissipate it.

Chris, I have read your comments. I don't think there is really that much disagreement.

I'm sure we have discussed before that how much the radiators will dissipate per unit time through convection and radiation is directly related to the current indoor temp and the temp of everything in the building. That delta T can increase by 40-50% from normal if somehow I was stuck trying to raise the entire structure from 0 degrees right?

We seem to be stuck on how much good results depends on the size of the boiler and and how much depends on the control. I am simply saying it is mostly control and that these sophisticated controls can do their thing quite well with oversize boilers. I don't know why this observation upsets people. I'm quite sure that those selling the controls sure hope I am right about that.

In your comments and others above I keep reading that at the end of the day already sophisticated algorithms need to become even more sophisticated to really get this right even with the "perfectly" sized boiler (whatever that is). I also keep reading things like "pulse" steam into radiators at just the right times to keep things even. And somehow needing more well timed "pulses" always seems to be where everyone ends up (including me). The original systems had infinitely small continuous "pulses" . Hmmm.

You say your favorite is 3CPH which also happens to me mine. I do 3CPH always in all conditions but vary the on/off relationship.

Honestly, I really don't see how we really are disagreeing about very much.

BobC

How about building yourself some Hoffman 2c vacuum vents to modulate the emitter temperatures.

Bob

ChrisJ

@PMJ
Perhaps there's just some confusion in the text.

One thing many seem to forget is that I downsized my boiler to make it easier to control, it had nothing to do with pressure. I noticed how Mark's system worked with the Ecosteam and mine was a lot harder to control, easier to overshoot etc. We even reduced my cycles to shorter times than normal to make it easier to control.

Dropping 25,000 btu/h was a huge improvement. I wish I could drop another 25,000 but I can't due to the size of the block and I refuse to reduce my manifold pressure as that also reduces efficiency. Kind of, counter productive in my opinion. When it comes to atmospheric boilers I'd rather a slightly over fired boiler over a slightly under fired one any day.

This is a big part of the reason I'm against oversized boilers. They're harder to control especially with a normal thermostat. This is why an outdoor reset is such a wonderful thing on a hot water system. It's very hard for the system to raise the temperature of the space and therefore very steady and easy for a thermostat to control.

That, and I feel using a Pressuretrol to control steam pressure seems pointless when the radiators can. Using your method is fine too, but shutting the system down with a safety limit (Pressuretrol) constantly just seems wrong.

PMJ

@ChrisJ

Just to clarify my method, I do have a constant run preheat when required. I then do 1 hour of 3 cycles 5 min fire/15 min off. If the tstat is not satisfied I switch to 1 hour of 3 cycles 8 min fire/ 12 min off. If the tstat is still not satisfied I switch to 3 cycles of 10 min fire/10 min off and stay there as long as necessary.

I have determined that the 5/15 is basically enough to keep the temp at least from falling under 90% of the conditions I face. The highest percentage run I ever need at -20F is the 10/10 50% duty. That gives you an idea how oversized I am - a lot, and plus as best as I can tell the gas regulator is 25% below full fire now. My calls for heat as the temperature goes down outside get longer and longer - 3-4 hours anyway. I may insert more steps yet to make calls even longer. My goal is to have the temperature rise in the deadband of the tstat as slowly as possible. Rads always hot - just really even heat with steam pressure never reaching 2 ounces - even with that huge boiler.

My point is that with even a bigger boiler than this one I would merely reduce the on to off percentages shown above - and easily achieve the same result. This boiler is way more than I need and if I have to replace it it will be with a smaller one. I would still get considerable extra but not this much.

We have now clearly hijacked this thread. My apologies to the OP.

Tinman

None necessary. Hijack away. All good stuff.

SWEI

ChrisJ said:

This is why an outdoor reset is such a wonderful thing on a hot water system. It's very hard for the system to raise the temperature of the space and therefore very steady and easy for a thermostat to control.

I agree with you on most of that, but the above does not quite match my experience. When an ODR curve is properly tuned, the thermostat becomes almost unnecessary. This is a good thing, because the thermostat ends up with very little authority. If it turns off the boiler, the room temp drops, then the boiler fires back up. Because of the low water temp (ideally just enough to keep the room at temperature) the air temp recovery can easily take an hour or more. This can be mitigated somewhat by using a very tight swing (like 0.5°F or less) but then you often run into false call issues from drafts, etc. The answer is to set the stat a couple degrees above the desired room temp to act as a high limit control. Once the curve is properly tuned, it responds mostly to external heat sources (solar gain, wood stove, etc.) and you get real comfort.

The best answer is proportional control of the flow and/or the boiler output. TRV's really rock with ODR.