Minimum run time setting on thermostat

RuffinoVino

I have a new ecobee thermostat and it has a setting for how many minutes the boiler will run. Sometimes if it's very cold and the boiler needs to run for 35 mins or so it must reach the cut out of 1.5 and shuts down for 4 mins or so then restarts. When it restarts the ste has obviously continued to radiate the radiators and usually satisfies the thermostat 2-3 moms after that latest start but I have the minimum run set to 8 mins so it them goes over the set point. What is a safe min run time to set the boiler on the thermostat?

pecmsg

Is the stat shutting it down?

Hows the air filter?

RuffinoVino

It's a gas steam boiler where is the air filter?

RuffinoVino

I just said the thermostat is not satisfied when it shuts down the first time....

EdTheHeaterMan

Depending on the way the thermostat is wired into the circuit, the thermostat minimum run time may still be counting down when to burner is off, because the call for heat from the thermostat does not account for any of the limit switches opening that will stop the burner. What boiler is your ecobee connected to? Brand and model number. Weil McLain EG is wired different from the Burnham steam boilers. And oil burners are even more fun.

RuffinoVino

It is a Weil McLain EG 

pecmsg

My mistake, Does the flame icon or whatever the t-stat uses to indicate its calling stay on and the boiler is shutting down by itself?

EdTheHeaterMan

Depending on your ecobee setup, the over temperature may be in the thermostat reaching temperature and shutting off the burner, then the left over heat from the cast iron will still radiate heat for several minutes after the thermostat is satisfied. You can enable the thermostat to learning to stop early as a result of the overheating, and it will eventually get it right. If you disable that feature, then the thermostat will never learn how early to shut off to prevent over-heating. Not all smart thermostats have that learning feature. I believe some, if not all ecobee thermostats do have that capability. But I'm not an ecobee kind of guy. Only set up about 5 or 6 for customers in the past 20 years. Not at all familiar with the mot recent stuff.

RuffinoVino

No the thermostat icon for heat stops displaying and the boiler shuts down. I believe it's exactly 5 mins. Then it only restarts if the thermostat hasn't been satisfied but if it is it obviously doesn't. The only concern I have is that if it does restart 5 mins later and within a minute the thermostat them gets satisfied since I have the minimum run time set for 8 mins it will continue for exactly 8 mins and the temperature in the house will exceed the set point. So my question is what is a safe minimum run time to set the the boiler on the thermostat? I'm assuming 1 minute is to short?

EdTheHeaterMan

pecmsg said:

My mistake, Does the flame icon or whatever the t-stat uses to indicate its calling stay on and the boiler is shutting down by itself?

I still thought it was a funny Query. Here is a slide from my class that illustrates hydronics (including steam) is cleaner than scorched air systems
Sometimes, it got a chuckle.

RuffinoVino

Any thoughts on the setting for minimum boiler run time on the thermostat?

Jamie Hall

Yes. Don't. A thermostat is a thermostat, not a timer or an alarm clock. Let it do it's thing -- which is to start the heat when it's cold and stop the heat when it reaches its set point (or, if it has the capability to anticipate a potential overrun, when it gets to that point).

RuffinoVino

You're not understanding the question and the thermostat Jamie. The thermostat which is an Ecobee has a setting called "Heat minimum on time" which obviously overrides the set point if the minimum run exceeds the set point. So my question is what should that setting be set to? I'm sure I don't want the boiler to turn on for 1 min and off if I set it to 1 min even though the thermostat may get satisfied after 1 min. What's the safe minimum run time for a boiler?

Jamie Hall

10 to 30 seconds.. I am understanding the question. There is no excuse for the boiler to run -- at all -- if the space does not need heating.

RuffinoVino

Again, the boiler shuts off after hitting the  cut out of 1.5 pressure for 4 mins and the thermostat is not yet satisfied. Then during that 4 mins the radiators are obviously still radiating heat and it increases the temperature but not quite enough when the 4 mins is up and the boiler restarts and since I have the minimum run time set to 8 mins it will run that time even if it only needed 1 min to satisfy the thermostat. So again, does anyone know what the recommended minimum setting run time is for a boiler?

pecmsg

I still don’t think it’s the stat that’s shutting off the boiler but the boiler control!

Jamie Hall

Stubborn, aren't you?

Jamie Hall said:

10 to 30 seconds.. I am understanding the question. There is no excuse for the boiler to run -- at all -- if the space does not need heating.

ratio

A minimum on time isn't what you want for this type of system. (If the stat is calling for heat too often, it is is mis-configured or not a good match for your system.) Set it to zero. Look for a minimum OFF timer, & set that to something that will allow the residual heat from the radiators to finish heating the room. Five minutes seems like a good starting point

Most modern stats are optimized for forced-air systems & require thoughtful configuration to use them on water or steam systems.

RuffinoVino

I'm not sure if I'm not explaining correctly or it's being misread. If anyone is familiar with the ecobee thermostat you will know it has a setting that is called "heat minimum on time". 

Problem: when it's very cold in the morning and the boiler set point is 3 -4 degrees lower overnight than the wakeup time the boiler sometimes will need to run 35-50 mins to satisfy the morning set point. After an estimate time of day 35 mins the boiler will shutt off for 4 mins. Now the thermostat has NOT been satisfied at the shut off. During the next 4 mins the house will continue to get warmer(I have Ecobee sensors in all rooms so I can see exact temperature on thermostat in each room) but the temperature won't quite hit the set point then the boiler restarts. 
After estimate (different all the time) of 1-2 mins the thermostat will now show it's hit the set point but is continuing to run for the full 8 mins that I have that min setting set to. After 8 mins it shuts off and about 15 mins later the house temperature has now exceeded the set point because it rat that additional 8 mins. 

My question is: can i set the minimum run time to 1 min or is that not good to have the boiler turn on and off for only 1 min of that is the minimum time the thermostat may need?

Jamie Hall

I don't think either @ratio or I have misunderstood you. We know that that thermostat has a setting for minimum run time, for reasons which I cannot understand -- but there it is. The time you should set it for is whatever the lowest setting for the minimum is -- one minute, if that's the lowest it will go. Zero, if it will let you do that.

dabrakeman

My first question would be why are you hitting 1.5psi. Is this just a an extremely cold day or are you recovering from a setback. If it is just a cold day then maybe you are way oversized on your boiler. If just when recovering from a setback there are ways to do that with the Ecobee to still avoid reaching Ptrol shutdown (1.5psi). I am an Ecobee owner and I sense you are getting a bit frustrated that nobody seems to be giving you a straight answer. I don't think there is a definitive answer to your question, at least not without knowing under what conditions you are shutting down off the ptrol and what your tolerance level is for a little overshoot. I will tell you that I have mine set at 10minutes. It is not "unsafe" to have the boiler come on for a minute and then turn off right back off but maybe better to avoid it if happening a lot because it is just more cycles on your auto damper (if you have one) and also as in my case, I don't like the idea of burning a minute or two of gas and not getting at least some heat from the burn it into my radiators. I changed it to 10 minutes from 1 minute because I do use a nightly setback and when reviewing my data it was bothersome to me how often it seemed that a cycle just started a few minutes before my thermostat called for the setback. I decided I would rather have maybe a little overshoot or artificially later setback than a useless 5 minute burn and no steam from it...

The Ecobee has a smart recovery which is like an anticipator and can be used if activated to try to minimize overshoot. I actually turned mine off because I wanted to do recoveries with my 30% oversized boiler. To do so I had to set a schedule to recover in precise 30min on 30min off cycles which the smart recovery would screw up... Sure I get some overshoot from time to time but I guess I have a higher tolerance level for an extra degree or two than I do for hearing my boiler run for 5 minutes and then shutoff before I get any heat😉. If the overshoot bothers you more then set min run time as low as you can (I can't remember if there is a zero or 1).

AdmiralYoda

I too have an Ecobee on my single pipe counterflow steam system with 5 sensors scattered throughout the house.

I have not messed with that feature and my system works perfectly. The advice I can give is DON'T use a temperature set back! In an ideal world your boiler would be sized perfectly to the sum of the EDR of your radiators and the system will never build enough pressure to trip the Pressuretrol/Vaporstat. It will condense steam as fast as it can make it.

Most systems are oversized and will build pressure, my system included. For years I used a deep night-time setback and the boiler would act in a manor similar to how you are describing. It would hit the pressure limit and slowly coast back to 0.5psi or whatever and fire back up. I believe this is what you are experiencing. I have switched to a "set it and forget it" at 68 degrees and I've actually saved a few bucks over the winter.

Here is an excerpt from Ecobee's website:

Heat Minimum On Time:
The minimum amount of time your furnace/boiler will stay on during a call for heat. This is set to 300 seconds (5 minutes) by default. If your furnace/boiler is engaged and then the call for heat is immediately cancelled, the furnace will continue running for this set value (5 minutes) before turning off. This setting prevents your furnace/boiler from short cycling, so we recommend leaving this at 300 seconds to prevent any potential damage to your equipment.

I think this more applies to Heat Pumps and Hot air furnaces than it does steam boilers. I've never messed with it and my oversized boiler works just fine. When it is fairly cold out, let's say 20 degrees my boiler runs for about 20-30 minutes every 1 hour or so and the house is cozy.

dabrakeman

@RuffinoVino: Was answering your 3:23pm post and now just saw your latest post. In your schedule is your recovery being controlled by the thermostat on the wall or by a remote sensor or and average. I stopped controlling by the wall stat because the wall is cold (mine are) and adds hysteresis relative to the real room temperature. You should be able to assign what device you want controlling each and every comfort setting in your schedule.

Jamie Hall

Perhaps I am being too abrupt. There are actually two questions here (at least), not one. One is, is there any harm to the equipment from having an extremely short cycle? And the answer to that one is no, particularly if your system is atmospheric gas, but equally valid for a power burner or an oil burner. As @dabrakeman pointed out, the most vulnerable piece of equipment is an automatic draught damper, if you have one of those infernal contraptions. So from the standpoint of the equipment, the shortest possible on time is best.

If this is a steamer, and the system is cycling on pressure, that small additional amount of fuel won't be wasted -- the boiler will convert it into an equally small amount of steam which will get to the radiators.

However, there is also an aesthetic question: just how bothersome is a short cycle to you? If you simply don't like it, that's fine, and then the question becomes how much overshoot would you prefer in exchange for a longer minimum on time? And I can't answer that one for you. That has nothing to do with the equipment, but only your personal preferences.

RuffinoVino

dabrakeman and admiralyoda you both understand the question clearly! I'm not sure why there are so many people on here that respond to questions that they either don't understand or have the knowledge which only further confuses the issue.

So yes, I set the "sleep" comfort setting to 64 then I have 3 additional comfort settings and have gradually increase in the morning as follows:

5:00am "pre wake up" 67
5:30am "wake up" 68
7:30am "Home" 69
11:00pm "sleep" 64

So the only time the boiler will I assume reach the cut out pressure is during the pre wake up going from as low as 64 to the 67. I have the pre and wake up broken down because I found having that big swing in temperature quickly is uncomfortable. 

Throughout the day during "home" schedule the boiler will run 1 time every hour to 2 hours depending on the outside temperature. Each run cycle is roughly 15-25 mins and NEVER shuts down from pressure, only when the thermostat is satisfied. 

So the only time the boiler shuts down without the thermostat being satisfied is that sleep to morning if it has to run for more than maybe 40-50 mins.

AdmiralYoda

@RuffinoVino It sounds to me like your system is working as expected. The nighttime 64 to 67 degree wakeup is a pretty good setback. My system would definetely cycle on pressure.

Perhaps the best way to combat this is to make the "Sleep" temperature 66 degrees, one degree less than your "Pre wake up" of 67. I'd be willing to bet you'd use less fuel.

RuffinoVino

I'm no so much concerned with the savings I prefer the comfort of cooler nights with a blanket. But my main concern was if I can lower the minimum boiler run time to 2-3 mins without causing any unnecessary stress on the boiler so I guess that's been answered with a yes it's fine to do that. 

Regarding the question about if I just use only the thermostat temperature for the set point or do I use an average of that with my 9 sensors is I use the average and almost always I have complete balance with every sensor the same temperature.

pecmsg

Your question should be
how oversized is my boiler if it can come up to that pressure that quickly?

RuffinoVino

What do you mean quickly??? Going from 64 to 67 in maybe 50+ or so mins isn't normal to hit 1.5 psi?

RuffinoVino

Pecmsg so your telling me you have a boiler that will run for an hour or more straight without cycling off going 3 degrees in temperature?

pecmsg

At design condition's here on eastern Isl of Long yes. 

5* outside air and a little wind I cancel my night set back. Pull the couch a little further away from the heaters and remove the cover from the radiator by the stairs. It will be most of the day to recover those 4*. The boiler runs continuously!

pecmsg

Those condition's happen once or twice a year. 

dabrakeman

The other "people" that answered here happen to be some of the most knowledgeable and nicest folks in the industry, people you will be glad that are there when you have some other real problem with your system. I'm just a homeowner like you who happens to have an Ecobee a well. There are mixed feelings on the forums about smart thermostats and setbacks but everyone is here to help. I personally see some benefits from both and have shared data relative to setbacks previously.

You may simply want to add additional steps in your recovery. Unlimited steps in your schedule with Ecobee. If you can only do say a max of 2 degree recovery without tripping the ptrol then you can tailor the schedule to prevent burns longer than 30 minutes in the recovery. Also, I assume you are running +/-0.5 degree and if wanting to minimize over shoots then also make sure your recovery steps are designated as "normally home". "Normally away" adds a 1 degree to whatever the set swing is.

RuffinoVino

And here are the pressuretrol cut in and differential settings. Don't these look set correctly?

dabrakeman

I do a 6 degree recovery but it is spread out over 3 1/2 hours. 30min on/off. 30% oversized boiler. Pressure never over 0.5psi including this weeks -2F morning.

RuffinoVino

Pecmsg it sounds like you have a serious insulation issue. I'm also on long island and my boiler runs almost never more than 1 hour even when it's 25 degrees outside. I would definitely check why your house is losing so much heat.

pecmsg

You’re missing the point. 

It takes 10 - 15 minutes of run time for the combustion process to settle down. 

At design conditions you want the boiler running non stop. 

RuffinoVino

Your telling me a optimal home boiler is running non stop for 24 hours a day??? Seriously, based on your previous comments and this one I think with all due respect your clueless.

pecmsg

RuffinoVino said:

Your telling me a optimal home boiler is running non stop for 24 hours a day??? Seriously, based on your previous comments and this one I think with all due respect you’re clueless.

At design conditions……Yes

pecmsg

Define your optional boiler?

HVACNUT

RuffinoVino said:

Again, the boiler shuts off after hitting the  cut out of 1.5 pressure for 4 mins and the thermostat is not yet satisfied. Then during that 4 mins the radiators are obviously still radiating heat and it increases the temperature but not quite enough when the 4 mins is up and the boiler restarts and since I have the minimum run time set to 8 mins it will run that time even if it only needed 1 min to satisfy the thermostat. So again, does anyone know what the recommended minimum setting run time is for a boiler?

2 minutes minimum run time if it can't be set to 0.
Is there a minimum OFF time?

You lose the heat icon on the thermostat when the burner circuit opens at 1.5 psi even though there's still a demand?
That's not right if that's what's happening. 

Are you also using a remote sensor and averaging?