how long should boiler cycle be?

Joe_39

Like raising it from 65 to 70 in one shot??

The steam does come up rather quickly

different answers on here... so should the boiler run continuously without building pressure or is building pressure normal even when rads are giving off heat???

Joe_39

On my steam boiler,

it takes about 10 minutes from a cold start before all the rads give off heat, then the pressure builds and it shuts down.. Then it restarts again until pressure hits about 2 and shuts down over and over until thermostat is satisfied.

My questions is on the restarts, those seem to last about 2 mins on and 2 mins off, it seems like a waste of fuel to restart over and over again.

Is this normal? Is there anyway to keep the boiler running continuously until the tstat is satisfied?

1 pipe steam,gas, boiler is properly sized for the sq ft of rads/piping in house

patrick linhardt

cycle rate

Hi John,

No, this is not the way it should be. The boiler should run without going off on pressure until the t-stat is satisfied.

On one pipe steam, check the main vent(s). They need to be properly located, working and sized. Have a heating professional check it. The short cycling you describe is wasting fuel and wearing out the gas valve.

What area of the country are you in? Maybe someone on the wall here can help you.

Best regards, Pat

Alan(CaliforniaRadiant)Forbes

Could it be

an oversized boiler? Have there been a lot of radiators removed?

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Mike20

Over sized or over fired

I agree that this sounds like too much boiler for the home or building -

Have a qualified heating contractor do a heat load calculation on your home to determine how much heat you actually need - Then compare that with the size of the boiler and the firing rate of the burner.

If this is an oil boiler you may simply need to change the nozzle size to change the Firing rate of the burner-

Make sure that the burner is adjusted with someone that is experienced with using Combustion Efficiency test equipment to assure that your burner fuel air ratio is set correctly.

Good Luck
MG

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[Deleted User]

Sounds like an air problem...

As the host of this wonderful web site is known to say, "the solution is rarely in the same room as the problem".

I suspect air vents at the end of main and radiators are undersized, causing the steam to compress the air, causing the pressure switch to kick in before its time.

Remember, air and steam cannot occupy the same space at the same time...

Get rid of the air, and the steam will make the radiators hot, thereby delivering the goods to the thermostat (heat) that the thermostat was looking for.

ME

will smith_4

cycling

I'd bet it ends up being a problem with venting, but even when all the vents in the system work properly, the sysetem will still cycle through the pressuretrol until the stat is satisfied. That's just the nature of the beast.
One other possibility: If you have a mercury type pressuretrol, it has to be level to work correctly, and it also has to be installed with the pigtail in the correct position.

Rodney Summers

John Q,

Anytime you heat up all rads, fully, from a cold start in 10 minutes your burner is overfired for sure, and may be oversized as well. I would guess by a factor of 2, at least!

It makes no difference whether or not you go from 60° to 65, or 65° to 90. Anytime a boiler can go from a cold start to all rads heated to the ends in ten minutes the problem can only be one thing. The boiler is overfired.

You state it's gas. You also state the boiler is sized for the EDR rad/load. Clock the meter (if it's NG) and determine what the gas rate is compared to the boiler plate input rate. If it's LP, check the pressure at the manifold.

Regaredless of which it is, it is definitely getting much more fuel than it should. The absolute minimum time it should take for a cold start to all rads hot from one end to the other is maybe 15-20 minutes. I prefer 25 to 30 for a cold boiler (70° boiler water temp) to all sections of all rads to be steamed/hot. Even 35 is okay.

Something's wrong.



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gerry gill

in a perfect world

the pressuretrol should not operate..the t-stat should only operate..just like Pat said...it was easier to do with coal than gas..once your main gets hot, your boiler is effectively oversized by 1/3rd.

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Joe_39

I may be off about the cold start time,

Im working off of memory from last winter. It may be 15 to 20 mins... house is small ,the main is only about 30 feet with a large main vent near the end.

But definitely after all rads are heated (and they all get hot at around the same time give or take a minute) the boiler will shut off on pressure before the thermostat is satisfied- but all rads give off heat - it never shuts on pressure before rads are giving off heat.

I understand what somebody said that once pipes/rads are hot the system is 1/3 oversized..

I thought it would be optimal if the boiler ran continuously and never build any pressure and only shut off when the thermostat was satisfied.

But i guess once the steam is in all the pipes and rads it cannot disappate as fast and will cause pressure to rise???

Am I asking for too much here??? I read about short-cycling but from reading up on that it said short cycling is when boiler is on/off repeatedly with NO HEAT from rads.. I do get heat..

would adding a second main vent help the boiler run longer??

will smith_3

huh?

The thermostat is not the operating control-it tells the boiler it's time to dance, then the boiler fires up and cycles off the pressuretrol. Period. The boiler will cycle off the pressuretrol TILL the stat is satisfied. Now, where the stat is located is one thing, and whether or not all the vents work is another. At the end of the day, the pressuretrol has the final say of when the burner cycles on/off.

patrick linhardt

might need a Dan H. intervention

Hi Will,

We are looking at the same thing, but with different perpectives.

I'm from the old school of coal fire. Hand-stoked slow burn fire to heat the water up to steam temps. Large steam chests and plenty of outlets to assure dry steam. Steam slowly moving out of the boiler, heating cold iron as it moves, pushing air to the vents. All the while the damper regulator is modulating the draft doors in reaction to any build-up of pressure as steam fills the system. Working on as low a pressure as possible because low pressure uses less fuel.

But the old school and perfect worlds do not exist. Our reality is automatic fired burners, generally at full blast till either the t-stat or safety turns it off. The traditional solution is extra large venting to prevent air being pressurized in the system by the quick-to-steam modern boiler, causing the safety/operating (pressuretrol) control to cycle. I have seen and been told of many systems that cycle on the t-stat without ever showing any pressure on the gauge or shutting off on pressure. I like that, it's a good thing.

My goal for a sytem is to cycle on t-stat, not on pressure. Reality is some cycling on pressure is going to happen. If it happens a lot, then look for causes, like over-fire, under-venting, over-sizing, bad piping, dirty water, etc.

Best regards, Pat

Mike T., Swampeast MO

Could the thermostat be the culprit as well? T-stat not suited to steam heat? T-stat defective but still functioning? T-stat anticipator defective or improperly adjusted?

patrick linhardt

anything is possible

Hi Mike,

Good question, you never want to overlook something. The type of t-stat and its adjustment can affect performance. However, from the info provided, checking the venting rate, firing rate, near boiler piping and boiler sizing would come first.

Best regards, Pat

David Hohengasser

Vaporstat

Comments mention low pressure steam being most efiiceient. I replaced the pressuretrol with a vaporstat. It is set to cycle between 2 ounces and 12 ounces pressure. Is the differential too large? Should it be increasesd? I am trying to reduce cycling on a boiler that is about 25%-30% oversize. All mains are vented and sized properly.

michael_15

Insufficient radiation

Perhaps your boiler is more oversized than it seems if you don't have sufficient radiation aside from the nominal EDR of the radiators. Covers on radiators? Metallic paint? Your piping vs. radiation load ratio may be especially low, meaning the 1.3 pickup factor is a bit on the high side. I suppose this is more likely on a 1-floor house with all of the radiators (mis)-placed in the middle of the house right next to the main.

-Michael

will smith_4

no interventions on the weekend!

Hi Pat-
I understand what you're getting at. I take care of several 40+ unit apartment buildings that were once cycled off of condensate temp that I've put remote sensing stats on; before the remote stats, in the winter, half the tenants had their windows open-it got so hot it would take your breath away. Now with a stat set at 68 at the furthest point from the boiler, pressuretrol at 1.5 cutout 1/5 cutin and all the vents working, all is well. The boilers used to be coal too, now gas. I'm just used to seeing these lower volume puppies. Here in the Chicago area, I'm just glad to see ANY steam system. More often than not, suit and tie salesmen that don't know what they're looking at convince owners to rip 'em out for forced air.

patrick linhardt

thanks for sharing

Hi Will,

It is always good to hear about a system that is working fine. I also hate to hear the familiar scenario of ripping out steam systems because someone doesn't understand the problem.

Glad to hear all is well. I suspect its good venting, low pressure and your attention to maintenance.

Best regards, Pat

gerry gill

assuming,

all the vents are good and plentifull etc.etc. if the boiler cycles on pressure it is then firing higher than the connected load can condense..thats not desireable.

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steve_6

No intervention needed

Gerry and Pat are absolutely right. If the system is vented properly and the boiler is fired to the connected load the boiler should "not" cycle off on pressure!

Joe_39

should I raise the pressuretrol setting??

I know that is a no-no in Dans book, but in this situation raising the pressure would let the boiler run longer and reduce the time between cycling..

Which is the lessor of 2 evils, frequent pressure cycling or running at higher pressure?

patrick linhardt

no evils please

Hi John,

There is no lessor when both options are evil. Frequent pressure cycling and running on higher pressure are both bad options and usually can be corrected with repairs, adjustments or corrections that pay for themselves in lower operating costs. Why not do the right thing?

Best regards, Pat