Possible to vent mains too fast?

Motorapido

It's not possible to vent mains too fast on single pipe steam, is it? I know if you vent a radiator too fast, the vent closes before the radiator has had a chance to fill with steam in most of its sections. I can't imagine any harm in massive main venting, other than going broke with Big Mouth purchases. The reason I ask is that although I have already achieved 100% of my venting capacity on a branch main that offers just one 3/4 inch tapping, on which I have an antler with 3 Big Mouths (which slightly exceed the venting capacity of that 3/4 inch tapping), at the end of my primary main, where I already have an antler with Big Mouths, there is another tapping next to the antler, 1 inch, with a plug in it, and I could open that tapping and put in enough Big Mouths to max that 1 inch tapping (probably 4). No harm in massive main venting, other than financial pain from buying Big Mouths, right? Please advise.

One thing I should note is that my boiler is about 40% oversized. I cycle on pressure on some calls for heat, with my pressure limited to 1 pound cut out (I adjusted the calibration screw on my pressuretrol to allow it to cut out at 1 pound). I plan to add a Vaporstat this year or next year. You could argue that with even more massive venting on my mains, and my current 1 pound cut out and future plans to lower the cut out further, I would run an even shorter first cycle, since the boiler would not have to run as long while the air vents out of the mains. Any subsequent cycle following a first cycle on pressure would be shorter, too. I know that puts more wear and tear on the valve and the automatic damper and gives the flue and chimney less time to get really hot. But I'd be burning less gas, which is a good thing. Am I over-thinking this?

Kahooli

Have you investigated downfiring your burner? Money may be better spent on a tech doing that than adding another vent

Motorapido

There seems to be huge disagreement about down firing. Some say that deactivating the outside two burners can cause problems from uneven hx temperatures, combustion issues and air flow turbulence. Others say they do it all the time without downside. Some recommend replacing all burner orifices with smaller drilled orifices and others claim that creates trouble. Some say to simply reduce the gas valve outlet pressure a wee bit and then double check flame and co2. A new two stage burner and controls might be perfect, but not sure about ROI. For now, I'm just curious to see if more main venting is good or if you can overdo main venting.

BobC

No such thing as too much main venting as long as multiple mains are vented proportionately so the system is balanced. There is a point at which it becomes uneconomical to add further main venting.

For the record my 2" main is about 15 ft long and I have a bigmouth on it.

Bob

Fred

You can't over vent a main but you can put more vents on it than the tapping can accommodate, at which point you wasted money on the extra vents.

acwagner

I agree you can't over vent a main, but as @BobC said you want to keep all your mains and main branches vented such that they heat up about the same time. If one is maxed out on venting, making the other vent much faster might unbalance everything.

What's your overall goal in increasing the venting? Reduce time to satisfy thermostat? Reduce energy use? Better comfort? Just curious, but there may be other approaches depending on what your goal is.

gerry gill

i don't see how you can over vent a main. But at some point it becomes a waste of money. You will at some point reach the point where the steam is moving as fast as its going to go, no matter what you do.

Jamie Hall

gerry gill said:

i don't see how you can over vent a main. But at some point it becomes a waste of money. You will at some point reach the point where the steam is moving as fast as its going to go, no matter what you do.

Which, if you are starting with a cold main, can be surprisingly slow!

mikeg2015

Possibly. If your main is understudied in relationship to the steam flow rate, then venting too fast (radiators and mains combined) will reduce pressure, which increases steam velocity. I'd argue if you add more back pressure, steam velocity goes down a little and your more controlled. So the solution may be the ratio of main venting to radiator venting. Then also the ratio of steam output and main cross sectional area.

For boiler de-rating, it's probably better to add a cycle timer to reduce duty cycle (10 minutes on, 5 minutes off = 66% capacity) than down fire. With down firing, you effectively end up with too much secondary air and throw extra heat up the stack. Try is a $8-10 adjustable "Delay on break" anti-short cycle timer. Have the system wait maybe 3-5' after the vaporstat is satisfied before it can fire again (wire it to the 24VAC controls only, keep pressuretrol at 1.5 or 2 psi on main power circuit). However, this won' fix the balance issue necessarily.

Fred

@mikeg2015 said: Possibly. If your main is understudied in relationship to the steam flow rate, then venting too fast (radiators and mains combined) will reduce pressure, which increases steam velocity. I'd argue if you add more back pressure, steam velocity goes down a little and your more controlled. So the solution may be the ratio of main venting to radiator venting. Then also the ratio of steam output and main cross sectional area.

WHAT?

Jamie Hall

I'd just like to throw a little additional physics into the can you vent too fast/how fast can the steam move.

You have two factors involved in the time which it takes for steam to arrive at the end of the main. The first is, as is pretty simple, the simple rate at which air can be exhausted from the main. That's your venting. Now, if you were dealing with a main which was already hot -- nearly steam heat -- that is very close to how fast steam would arrive at the end of the main.

But.

In many cases that main isn't hot. In that case, while the steam in the hot portion of the pipe may be moving right along, the actual front of the steam -- the point where the steam meets the air -- won't be. At that location, the steam will be condensing on the cold pipe, and heating the pipe. The front will move only as fast as the arriving steam can heat the pipe, and the air beyond that point will only move as fast as the front is moving. There are a lot of variables involved, but for a well insulated main it seems to work out at about half a cfm for a 3 inch main is about what you can expect. If your vents can handle that, that's all you need.

This is why, on the system in the main building I care for, one Gorton #2 and one Hoffman 75 (installed on the dry returns at the boiler -- it's a Hoffman Equipped System) is quite adequate for 3 3" mains with a total length of almost 200 feet (the pressure at the header, once steam is raised, holds at a bit less than one ounce until all the radiation is satisfied, for the curious).

Motorapido

> @mikeg2015 said:
> Possibly. If your main is understudied in relationship to the steam flow rate, then venting too fast (radiators and mains combined) will reduce pressure, which increases steam velocity. I'd argue if you add more back pressure, steam velocity goes down a little and your more controlled. So the solution may be the ratio of main venting to radiator venting. Then also the ratio of steam output and main cross sectional area.
>
> For boiler de-rating, it's probably better to add a cycle timer to reduce duty cycle (10 minutes on, 5 minutes off = 66% capacity) than down fire. With down firing, you effectively end up with too much secondary air and throw extra heat up the stack. Try is a $8-10 adjustable "Delay on break" anti-short cycle timer. Have the system wait maybe 3-5' after the vaporstat is satisfied before it can fire again (wire it to the 24VAC controls only, keep pressuretrol at 1.5 or 2 psi on main power circuit). However, this won' fix the balance issue necessarily.

Can you recommend a particular timer?

acwagner

This is the timer I use:

http://www.galco.com/buy/Macromatic/TR-6512U

I have a slightly different approach to the location of the timer. Instead of on the pressuretrol, mine is just after the thermostat in series. Basically, thermostat calls for heat, which activates the timer, which cycles the boiler on/off until the thermostat is satisfied. I figure if I'm making any pressure, it means all my vents are closed and I'll overheat my house.

I'm not sure if this type of timer will work in conjunction witht he pressuretrol. But, it accepts all forms of electrical input, and has huge timer ranges. If you get this one, be sure to buy the socket it mounts into as well.

I've only been using it for a month or so, but I'm pleased with the results. My boiler is only about 15% over sized, nothing crazy. But we do large setbacks at night for comfort, and the timer allows the system to recover without building any pressure and short cycling.

But, if your system isn't balanced, the timer might make it worse. Your radiators need to all get steam about at the same time. Maybe a few minutes apart. That's been my experience.

thfurnitureguy_4

I am starting to like timers as solution for oversized boilers. It lets the boiler run at full bore where it is the most efficient but cycles it off letting the room catch up.
I recently added a timer to help with an oversized boiler but controlled it with a vaporstat.
In my controls the thermostat calls, the system starts instantly and runs until satisfying the thermostat. On a marginal day, the radiators fill part way and the rooms do not over heat.
On a cold day the call for heat is larger, the system will cycle on pressure. (boiler is more than 100% oversized to the installed radiation.)
My original plan was to just replace the old pressuretrol with a vaporstat. After years of hearing the logic of reducing pressure here on the Wall, I finally got the chance to make the change.
With the new vaporstat installed I wanted to get an idea of the potential savings from the new system. I installed it into the boiler but connected the switch to an ohm meter to witness the switch point. While operating with the old presuretrol (set to minimum) the boiler fired for about 20 minutes after the Vaporstat broke contact. So my cost spent on building pressure is about 20 minutes of burn time for each pressure cycle. As things usually go, with each change comes a new problem; without the pressure build up and drop off time the system was now switching on and off every few minutes, not ideal for efficiency and hard on the equipment, this gave rise to the timer idea.
My thinking was to run the radiators full on a cold day and cycle off using the vaporstat. The timer only times after a pressure cycle, so my radiators cook and soak while the timer holds the boiler off until the timer or the thermostat is satisfied. On a 20 degree day the system cycles on, builds 8 oz of pressure before being shut down by the pressuretrol, the timer latches in and holds for 30 minutes, by this time the thermostat has usually been satisfied. During the timer period the pressuretrol has reset but the timer prevents the restart of the boiler. If the thermostat is still calling the cycle will repeat until the stat is satisfied.
Parts were a box, timer, two control relays and a 24V dc power supply. A smart guy would have picked a better timer and possibly done without the relays and the DC supply.

mikeg2015

For an oversized boiler, just using delay on break (anti-short cycle timer) may be good enough on it's own. SO if it hits high pressure on vaporstat, restart is inhibited for a selectable time, maybe 5 or 10 minutes. During that time, the hot radiators will continue to put out heat and the call for heat should end.

Also, I have a upstairs and downstairs thermostat, so the timer will prevent short cycling due to uncoordinated calls.

mikeg2015

Fred said:

@mikeg2015 said: Possibly. If your main is understudied in relationship to the steam flow rate, then venting too fast (radiators and mains combined) will reduce pressure, which increases steam velocity. I'd argue if you add more back pressure, steam velocity goes down a little and your more controlled. So the solution may be the ratio of main venting to radiator venting. Then also the ratio of steam output and main cross sectional area.

WHAT?

Haha... sorry, meant "undersized" not understudied.

The point is that the size of the main is fixed, and you have to squeeze ALL the output from the boiler onto the main. Steam volume increases as pressure decreases. So to decrease steam volume you need more pressure. to build more pressure you need to vent slower. Plus, if you vent radiators too fast, then the steram goes down the runouts instead of heading first to vents at the end of the main.

Because the main is relatively small for the 300k BTU I'm sending to it at <1oz of pressure I'm getting a lot of back pressure early on in the main, and steam is heading for run outs. To combat this, I added vents along the way to reduce that back pressure from pipe friction and pressure drop on elbows.

Make more sense?

EBEBRATT-Ed

Yup. Some overthinking going on.

About the only thing that makes sense is a "heat timer system" which I don't care for. They put a control at the end of the steam main which senses steam at the end of the main. They call this "heat established" Once heat is established the burner is cycled on timer, length of run determined on the outdoor air temp.

Fred

Also, I don't think you decrease steam volume, unless you have some form of staging, on the burner, the boiler puts out whatever it is rated to output, of course until you build enough pressure that the controls shut the burner down completely. Steam speed slows down with pressure, not volume.
Compressing the steam/air in the mains, with smaller or no main vents just starts to push steam out into some of the run-outs. That's why it makes sense to properly vent the mains before trying to balance the radiators.

mikeg2015

Fred said:

Also, I don't think you decrease steam volume, unless you have some form of staging, on the burner, the boiler puts out whatever it is rated to output, of course until you build enough pressure that the controls shut the burner down completely. Steam speed slows down with pressure, not volume.
Compressing the steam/air in the mains, with smaller or no main vents just starts to push steam out into some of the run-outs. That's why it makes sense to properly vent the mains before trying to balance the radiators.

Since the pipe size is constant. If steam speeds up, it therefore has more physical volume... or rather less density. But yes, the mass of the steam generated will be directly related to boiler output. But the volume it occupies and therefore it's velocity, depends on the pressure.

I agree, and now have seen for myself, that until the main is venting correctly, you cannot balance the system.

Motorapido

thfurnitureguy said:

Parts were a box, timer, two control relays and a 24V dc power supply. A smart guy would have picked a better timer and possibly done without the relays and the DC supply.

Has anybody created a nice drawing and parts list for a cycle timer? I'd like to install one.

acwagner

I suppose every system and setup is different, so a universal parts list and drawing probably isn't possible. Where do you want to hook it up--on the vaporstat or after the thermostat?

If you put it after the thermostat like I did, the parts list is probably limited to the timer I gave in the link to above, the socket it mounts into, appropriately sized wire for the voltage on your system, and some wire nuts. That's all I needed. The timer cycles between on and off, and all you have to do is turn the dials to adjust the times. Just be sure to get the version of the timer that is "on" first in the sequence. The link should take you to the correct one.

Personally, I had to solicit help to figure out the wiring. The timer accepts all current/voltage inputs, so you don't need the DC power supply.

mikeg2015

I didn't end up installing mine, but here's the one I bought.

$24 http://www.supplyhouse.com/ICM-Controls-ICM306-ICM306-Duty-Cycle-Timer-Time-Delay-in-Seconds

Here's the anti-short cycle timer I'm using. It's a whole $5.95, better save up ... http://www.supplyhouse.com/ICM-Controls-ICM203-ICM203-Delay-on-Break-Timer-03-10-Minute-Knob-Adjust-Delay

Motorapido

mikeg2015 said:

I didn't end up installing mine, but here's the one I bought.

$24 http://www.supplyhouse.com/ICM-Controls-ICM306-ICM306-Duty-Cycle-Timer-Time-Delay-in-Seconds

Here's the anti-short cycle timer I'm using. It's a whole $5.95, better save up ... http://www.supplyhouse.com/ICM-Controls-ICM203-ICM203-Delay-on-Break-Timer-03-10-Minute-Knob-Adjust-Delay

Thanks, Mike and ACWagner. Wonder if down the road when these switches fail at the end of their lifespan if they fail in the ON or OFF mode? I'd hope they would fail in the ON mode. That way, if the switch crapped out, the boiler would still run, and just cycle on pressure from the pressuretrol. Otherwise, I would need to give my Commander In Chief a little lesson in troubleshooting if I am out of town, the switch fails and the boiler does not run. She is a good student, but doesn't like additional mechanical complication in life. So if these fail in the ON mode, that would be beneficial.

acwagner

I'm considering adding a bypass switch just for the reason you stated and general troubleshooting. I don't know what the typical failure mode of my timer is or its effective lifespan. I suspect since it starts as a closed switch, it would fail closed. I hooked it up as a proof of concept, but I'm considering making it permanent. If I do, I'll put the bypass switch on and also adjust the wiring diagram so if some tech had to come in to work on it and I'm not around, there would at least be documentation of what it is and how it's wired.

I supposed that's an overall drawback to personalizing your system like this. It'll run better (or run how you want it to) but it makes it more difficult for someone else to troubleshoot it without you.

Motorapido

acwagner said:

I'm considering adding a bypass switch just for the reason you stated and general troubleshooting. I don't know what the typical failure mode of my timer is or its effective lifespan. I suspect since it starts as a closed switch, it would fail closed. I hooked it up as a proof of concept, but I'm considering making it permanent. If I do, I'll put the bypass switch on and also adjust the wiring diagram so if some tech had to come in to work on it and I'm not around, there would at least be documentation of what it is and how it's wired.

I supposed that's an overall drawback to personalizing your system like this. It'll run better (or run how you want it to) but it makes it more difficult for someone else to troubleshoot it without you.

That bypass switch sounds like a good plan. Make sure to post the results that you're seeing after making this change. My pressuretrol currently cuts out at around 1.5 pounds. I have already done the calibration adjustment to get it to 1.5 pounds, and I could probably pull it down farther. After I add the timer, I think I will try to calibrate it down to cut out around 12 ounces or so if I can get it that low, then set the timer for 10 minutes off, and see if that gives the radiators enough time to get the heat into the room to prevent short cycling. If I can get the cut out down to 12 ounces-ish, I don't think I will bother buying a vaporstat. We'll see.

PMJ

You guys are on the right road with the timer. Shortly anyone trying it with a system that shuts off on any pressure setting first will find himself thinking to use the timer to never get to pressure even the first time. Enough pressure to stop on is by itself proof enough that too much steam is out there for the conditions already. As you work yourself along this road your heat will just get more and more even.

Just document your work with a wiring diagram and explanation to put on the boiler so if a pro ever is called in he can see clearly and quickly what has been done and how to get back to conventional control easily.

acwagner

"Shortly anyone trying it with a system that shuts off on any pressure setting first will find himself thinking to use the timer to never get to pressure even the first time. Enough pressure to stop on is by itself proof enough that too much steam is out there for the conditions already."

This is exactly why I didn't put my timer on my pressuretrol/vaporstat. My system operates at really low pressure, around 0.5" WC. It doesn't build any pressure until all the vents are closed, and my radiators are oversized for the heat loss of my house. I don't need my radiators at 100% full for a normal call for heat. Higher pressure really isn't accomplishing anything, in my opinion. I'm sure some would disagree with that. In any case, a vaporstat can't control at that low of a pressure, so the timer solves that. My vaporstat is just a safety device now, as it should be. It'll never trigger unless something is wrong.

BUT, for this to work your system needs to be really balanced.

Motorapido

acwagner said:

"Shortly anyone trying it with a system that shuts off on any pressure setting first will find himself thinking to use the timer to never get to pressure even the first time. Enough pressure to stop on is by itself proof enough that too much steam is out there for the conditions already."

This is exactly why I didn't put my timer on my pressuretrol/vaporstat. My system operates at really low pressure, around 0.5" WC. It doesn't build any pressure until all the vents are closed, and my radiators are oversized for the heat loss of my house. I don't need my radiators at 100% full for a normal call for heat. Higher pressure really isn't accomplishing anything, in my opinion. I'm sure some would disagree with that. In any case, a vaporstat can't control at that low of a pressure, so the timer solves that. My vaporstat is just a safety device now, as it should be. It'll never trigger unless something is wrong.

BUT, for this to work your system needs to be really balanced.

Questions: I have maxed my venting capacity on mains with 5 big mouths and a Gorton2. Radiators on first and second floor all heat well and all rooms seem evenly heated. I currently build to 1.5 pounds pressure before cycling on pressure. Then about 3 minutes or so -- maybe more -- until it drops to a few ounces and starts another cycle. With delay at the triggering of the next cycle until the burner gets to full burn, the pressure needle drops from a few ounces down to about the 0 on the low pressure gauge. I would like to install a vacuum gauge, too, wondering if 0 pressure equates to open atmospheric pressure, or just the 0 on the pressure gauge and possibly some vacuum. I would like to hope that my main vents and radiator vents will stay closed as the pressure drops from the first cycle, and if I add a 10 minute delay timer, I would hope the system would remain in natural vacuum, making the next heat cycle faster due to vacuum. I do not know when main and radiator vents open after a heating cycle or how to measure this. I could do a smoke text at the vents if I had somebody in the boiler room reporting on the pressure reading and then during the 10 minute time-off cycle delay. Can I safely guess that I would remain in natural vacuum duing the 10 minute delay? That seems to be the ideal, since no new air would rush in, only to have to be purged out when steam built again. Any data available on when the main and radiator vents re-open?

Jamie Hall

Opening or closing for vents depends on the particular vent itself. Different makes and models will behave differently. Most of them, however, will open on a vacuum. The Hoffman 76 -- a main vent -- is particularly designed to maintain a vacuum. If the vent is thermally actuated -- as many are -- you will find that there is a wide range of temperatures at which they will reopen. Some are as low as 140 (I believe that Gortons open around there) while others are much higher.

acwagner

There are a few threads discussing theoretically converting a single pipe set up to be vacuum setup. I've been thinking along the same lines as you have. Most feel that the radiator vents will need a check valve configuration added to work, or basically adding a second line to each radiator. I haven't seen a post with results from someone just putting a compound pressure gauge somewhere on system without any modifications to the venting and seeing if the vacuum holds.

I've been meaning to add a compound gauge like you propose to do, but other projects have sidetracked me. If you do it let us know the results. I was thinking of adding it near the main vents so its more representative of the system vs the boiler vessel.

How often do you cycle on pressure?

PMJ

Compound gages are inexpensive and very useful to watch what is happening wherever.

I advise staying focused on what your goal is overall and how vacuum might help with that eventually. Assuming the goal is more even heat, then ever filling radiators enough to close vents on them is not what you want to do - ever. Even heat means partially filled rads over long periods of time and calls for heat that go on for hours. For this you will need even cycling of the boiler whether the system is vented or not. Even "well matched" boilers are making steam at a rate much higher than is required for normal heating day conditions. That rate must be slowed down somehow to really even out the heat. Vacuum will make it more even yet, but you still need the even cycling as the foundation so I would start there.

.

Motorapido

Hey Mike2015 -- for this timer http://www.supplyhouse.com/ICM-Controls-ICM203-ICM203-Delay-on-Break-Timer-03-10-Minute-Knob-Adjust-Delay
it appears that I simply wire the power output lead from the thermostat to the input on this timer, and then hook the output from the timer to that input wire on the gas valve -- essentially wiring it inline with the thermostat power wire. Am I correct? Is there no neutral or ground on this timer? Seems to simple and good to be true.
I will order the timer and also a vaporstat. Since I currently cycle on presure at 1.5 psi with my pressuretrol, I would still be wasting lots of fuel building pressure, even with the timer. I will start with the vaporstat set to 8 ounces, which seems like it would be more than enough, and then fine tune from there.
Also, I do not see any sort of mounting box option for this timer. It appears to have a hole from front to back. I could just screw it to a joist above the boiler, but mounting in a box might look more professional. Is there some sort of box mounting that I am overlooking?

PMJ

@Motorapido,

It is fine to start there but you will eventually really need a timer where you can adjust both on and off times independently. With both you can easily set cycles per hour and total burn time per hour. The next step is a PLC which will with one unit provide you with as many different combinations of cycles per hour/burn times as you wish for different conditions.

Gsmith

@Motorapido, I'm puzzled by your situation. From reading here and my own experience, it seems most single pipe systems are over-radiated, that is the radiators only really get hot all the way across at very cold outdoor temperatures (approaching design day in your area), so you might think about why you are building even 1.5 lb pressure. You have you said short mains and they are well vented, seems like at outdoor temps above design day you should meet the thermostat calls before building much pressure at all. This was the case at my house, which I personally knuckleheaded some years ago by putting very fast vents on the radiators and removing a large cast iron radiator in the room with the thermostat and replacing it with a 10 foot cast iron baseboard supplied from both ends. It didn't help that I had no main vents whatsoever. Reading here, I added big mouths to the mains, changed to slower rad vents, added very fast vents to the CI baseboard (drilled vent tappings at mid point of baseboard) so it would heat all the way across when needed, and replaced the old thermostat. Happy to report that my unbalanced heating system (hot upstairs, cold first floor) is completely resolved with well balanced heat (slightly colder second floor, warmer first floor as we like it). I did add a low pressure gage and vaporstat, but my system doesn't ever go much above 2-3 oz and always shuts down when the tstat is satisfied, not on pressure.

Much material has been posted on this site and in LAOSH about original design parameters, such as pressure losses of about 1 oz per 100 foot of main, so with short mains, it seems to me that most systems should not really required much pressure (who has 1600 feet of steam mains = 16 oz of pressure loss).

Are you using a setback? That might cause higher pressure needs as the tstat will not be satisfied till the system runs a while. I guess my point is perhaps you should think about why you are building pressure, after all, it doesn't cost much other than time to kind of retrace the system design parameters (EDR of rads, pipe lenghts, etc), maybe something easy to fix is causing the higher pressures--tstat; insulating mains, etc. In my case a lot had to do with an older mercury bulb tstat that I'm sure was physically slow to react--$35 easy fix.

I do like the idea of a vacuum 1 pipe system, but I'm not sure I would achieve much with adding a lot of complexity.

Just some food for thought.

Motorapido

Gary, I like your logical thinking and also your quest to optimize using only simple solutions. I hesitate to add any complexity to the wonderful simplicity of one-pipe steam. However, I have already addressed all the simple stuff. All mains well insulated last season. A few sags in mains corrected. Returns flushed. Boiler clean. Tons of venting on the mains. Appropriate venting on radiators, using Maid-O-Mist, with most using only medium orifices, and several using the smallest orifices. I cannot find my measurements of my mains right now, but memory tells me I have about 55 feet of main and another 60 feet of branch main (serving a one-story addition from about 50 years ago). So my mains are not short. They are not crazy long, but they are not short either. I cycle on pressure a few times when temperature is about 40 degrees or lower. Thermostat is a cheapo Honeywell digital. No setback. Set to 2 cycles per hour, steam setting, as I recall. I keep temperature at either 69 or 70, without setbacks. I like the reasoning that a 10 minute delay after the first cycle on pressure will allow enough steam to continuue entering the radiators to perhaps satisfy the thermostat without another boiler cycle, except for super cold days, when it might require a second boiler fire. I do not plan to go down the vacuum pump path, but simply to install the cycle delay switch between the thermostat and gas valve, to delay the next firing after it cycles on pressure. My boiler is about 50% oversized based on calculations of EDR I made last year.

Gsmith

ok, then, good luck and keep us posted. It helps all of us when other experiment and publicize the results.

acwagner

I agree with @PMJ with making the vacuum component "Phase 2" of your improvements. I'm still adjusting my timer setup. It takes some trial and error to figure it out.

I would offer that if you want to use the timer on the pressure control, then upgrading to a vaporstat makes sense. If you put the timer after the thermostat, then the vaporstat probably isn't worth the investment. Reason is you would set your timer setting such that the system never reaches any additional pressure than needed, so pressure control becomes a safety feature. Just my opinion.

Also, it sounds like your on top of your system, but cycling on pressure on a regular call for heat at 40 degree outside temperature seems unusual to me. Is around 40 degrees a "design day" temperature where you are at? I'm just curious.

Motorapido

I think I must be misunderstanding the function of the timer that I linked to. http://www.supplyhouse.com/ICM-Controls-ICM203-ICM203-Delay-on-Break-Timer-03-10-Minute-Knob-Adjust-Delay
I thought that if wired after the thermostat, it would allow the thermostat to call for heat until the pressuretrol shutt off the burner on pressure, and then prevent the continuing call for heat from reaching the gas valve until the delay time that I had set on the timer. I think I need a little more education on the function of the timer and its two potential applications -- after thermostat or after pressuretrol. Who can school me? Thanks in advance.

Also, not only is my boiler oversized, but three first-floor radiators were removed years ago (I can't put them back because the prior renovations removed walls and combined rooms, so no place to put the removed radiators back if I wanted to do so), compounding the oversize problem and the short cycling.

acwagner

You basically got it. The timer you're referencing needs an "off" condition to start. It'll need to be placed between the pressuretrol and the gas valve. When the pressuretrol switches to "off" because it hit the cutout pressure, that timer will start and delay the boiler refiring based on time not pressure (unless the time to reduce the pressure to the cut-in setting takes longer than the timer setting). It doesn't control "on" time, however, it only delays the burner from refiring.

If you put it right after the thermostat but before the pressuretrol I don't think it will do anything. Or, at least it won't delay refiring after cutout on pressure.

ChrisJ

> @acwagner said:
> "Shortly anyone trying it with a system that shuts off on any pressure setting first will find himself thinking to use the timer to never get to pressure even the first time. Enough pressure to stop on is by itself proof enough that too much steam is out there for the conditions already."
>
> This is exactly why I didn't put my timer on my pressuretrol/vaporstat. My system operates at really low pressure, around 0.5" WC. It doesn't build any pressure until all the vents are closed, and my radiators are oversized for the heat loss of my house. I don't need my radiators at 100% full for a normal call for heat. Higher pressure really isn't accomplishing anything, in my opinion. I'm sure some would disagree with that. In any case, a vaporstat can't control at that low of a pressure, so the timer solves that. My vaporstat is just a safety device now, as it should be. It'll never trigger unless something is wrong.
>
> BUT, for this to work your system needs to be really balanced.

0.5 " you say?

acwagner

Yeah. I didn't believe it at first--thought I had a bad gauge or a clogged pigtail or something. Using the conventional rules of thumb for pipe pressure losses I should be around 1.5-2.0 ounces of operating pressure. I purposefully ran the boiler so it would trigger on pressure, and the vaporstat cut-in/out settings corresponded dead on to what the gauge was reading. I also purposefully slowed my venting rates as a final check and the operating pressure went up when I did that. But, what finally convinced me is I saw some postings by you, @ChrisJ about how your system operates that low, too.

I honestly don't know how accurate my gauge is at the extreme low end of the scale like that, but I'm fairly certain it's in the ballbark.