Oversized Boiler / Vaporstat Question

DAZ_2

Will installing a Vaporstat in place of a Pressuretrol help if the boiler is oversized?

My system already rapid cycles due to the oversized boiler (based on reaching the temperature set on the thermostat). With my existing Pressuretrol, when I tried moving the "cut in" setting down, it seemed to make the boiler rapid cycle even more.

Is it possible that the Vaporstat would make my system rapid cycle even more than with the Pressuretrol?

It sounds like there are a lot of merits of the Vaporstat, but I am wondering if those merits are lost if the boiler is oversized.

Thanks.

nicholas bonham-carter

oversized boiler

1st, how do you know that the boiler is oversized? have you calculated the sum of the sizes of all the radiators?


i think the boiler would be suffering from under-venting, if it cycles on and off too much during a "burn". this is because it is squeeeeezing the air out through inadequate main line air vents. when your system is generously vented, and running on low vaporstat pressures, you will notice an improvement in comfort, and response. i don't know what your present pressure is, but i am sure it could be lowered to under 16 ounces, with great benefit. unless you know that the radiator vents are non-functional, focus on the mains, and increase their capacity with some gorton #2's.--nbc

DAZ_2

Oversized Boiler / Vaporstat Question

Thanks for your response.

There are several vents on each of the mains. The large supply main has a Hoffman #75 on one end, and a Gorton #1 on the other end (about 10 feet from each other). The other main (which I think might be a return main, but could be another supply main -- it is a two pipe system) has a Gorton #1 on each end (also about 10 feet from each other). All four of these vents have recently been replaced. Is it possible that more vents are needed?

The convectors, which are imbedded behind the plaster walls, have no vents on them. I was wondering if I could possibly install a vent on one end or the other of some of the convectors, particularly the few that infrequently get heat? I have included a couple of pictures taken from the top of one of the convectors.

I am pretty sure the boiler is oversized. It is a Weil McLain EGH-95 in a 3000 square foot house. A previous owner removed 3 of the 16 heating burner tubes from under the boiler.

Since I am considering installing a Vaporstat, I thought I would first try to lower the cut in on the existing Pressuretrol first. What I noticed is even more rapid cycling, and a pretty significant increase in the therm usage. This made me question whether a Vaporstat would be helpful.

Jamie Hall

Your comment

seems to suggest that you are basing the rapid cycling on reaching the temperature setting on the thermostat, which I would interpret to mean that the boiler/heating system heats the space very quickly, then reaches the set temperature, stops, and then the space cools enough to turn the system on again quickly.

This could mean the whole heating system is oversized, not just the boiler. It could also mean that the thermostat, not the pressurestat, is not working properly (thermostats are not quite as simple and innocent as they seem).

However, if the system is cycling on pressure, I go with nbc for step one: make sure your venting is adequate. Really adequate. Unless the boiler is really wildly oversized (like two or three times what is needed for the system EDR and pickup load), it won't short cycle until well into the heating cycle -- 10 or 15 minutes is typical. Unless the venting is bad.

Step two, after you have ensured that your venting is adequate, make sure that, if this is a two pipe system, that your traps are working properly (or that the orifices or valves are set right, for that type of system). Even one bad (stuck open) trap could cause cycling problems.

Step three, add up the EDR of your radiation and compare it to the boiler rating.

Step zero, if you haven't done it already, get Dan's books -- 'A Steamy Deal' -- from this website.

DAZ_2

Oversized Boiler / Vaporstat Question

Yes, the rapid cycling is as you described. Prior to my lowering the cut-in on the Pressuretrol, the boiler was turning on and off based only on reaching temperature according to when the thermostat called for heat. The system never reached a high enough pressure to have the Pressuretrol turn it off.

I have thought that I should replace the thermostat, since it might be contributing to my issues.

The short cycling is quicker than 10-15 minutes. I need to time it, but it is more like 7-9 minutes, sometimes shorter.

I believe the system does not have traps, but rather is equipped with built in orifices in the supply headers of each convector (according to a tag I found attached to the supply header).

Thanks for your insights.

Jamie Hall

so far so good!

The real question, of course, is: is the temperature in the house comfortable and even? That's the bottom line!

I am not qualified to comment on downfiring a gas boiler by removing burner tubes; hopefully someone else who is may comment on that.

The rapid (and it is rapid) cycling on the thermostat strongly suggests that the thermostat may need tweaking, if not replacing. With cast iron radiation, I would say that the boiler should only run about once per hour, for perhaps as much as 20 minutes (probably cycling on pressure towards the end of that time). Your convectors, though, don't have the mass of cast iron, and perhaps running once every half hour or so will be better. There are some programmable thermostats available (the Honeywell VisionPro is excellent) which can be programmed to do just that. Running the boiler longer, less often, will also help a lot in getting heat to those convectors you mention which don't get much heat. So will substituting Gorton #2's for all of the vents (the Hoffman 75 is a good vent, but pretty small).

You don't need vents on the convectors with a two pipe system!

With an orifice system it is important to keep the pressure low. Otherwise, steam will be forced through the convector and get into the returns, where you most certainly do not want it. If the returns are available -- and your comments suggest they are -- there is a fairly simple check on that: a return which is nice and warm -- you can hold your hand on it for a bit -- is fine. A return which is downright too hot (sometimes referred to as the ouch! or aiyee! test) is getting steam; in an orifice system, that means the pressure is too high.

At this point I wouldn't worry about the pressuretrol vs. vapourstat question, unless you are getting steam into a return somewhere. Check that thermostat first and get it right.

Larry C_13

Thermostat

DAZ, If the thermostat is the common round Honeywell style with a mercury switch, for proper operation, it has to be mounted so that it is level.

Larry C

Larry C_13

double post

Dan C.

If the boiler is already short cycling on pressure then adding a vaporstat is going to make it worse.

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DAZ_2

Oversized Boiler / Vaporstat Question

Thanks again for the responses.

With respect to the question of whether the temperature in the house is comfortable and even -- this whole thing started because several convectors were infrequently getting heat (only when the thermostat was moved up dramatically, but never once temp was stabilized), and the boiler feeder was turning on a lot (likely caused somewhat by steam escaping from the old Hoffman valve which has since been replaced). I also have to contend with a poorly insulated house. The temperature on the 2nd floor is typically 4-8 degrees colder than the 1st floor, due to poorly insulated walls and a poorly insulated attic (the latter of which I am working on).

Based on your responses, I will definitely replace my thermostat. I currently have a Honeywell Chronotherm III that works on a 1 degree temperature differential. I spoke to Honeywell, and they said that all of their current thermostats work on a 1 degree differential, except for the old round style. Do you think replacing with a new thermostat with a 1 degree differential is enough? Do you think finding a thermostat with a 2 degree differential would be better, and might result in less frequent cycling?

I will also replace the 3 Gorton #1s and the Hoffman 75 with 4 Gorton #2s (they are only 1 week old!). Do you think the 4 Gorton #2s should be sufficient? I assume, based on your posts, that it is not possible to over-vent?

And then, I still need to figure out if there is a way to modify or derate the oversized boiler to accomodate the house's current needs. In addition to the prior owner having removed 3 of the 16 burner tubes, the volume of natural gas being fed to the boiler was recently turned down.

All of my returns are always cold to the touch, so I don't think the pressure has been too high, or that I am getting steam in the returns.

One other question I had -- do you think the orifices might need to be replaced in the 2 convectors that work only infrequently? I sometimes hear a gargling noise on the supply side of those 2 convectors as they struggle to get heat. It sounds as if some water may be trapped in there somewhere.

Thanks again for all of your help!

Jamie Hall

Well now...

it isn't so much the differential of the thermostat as it is the cycles setting. The newer electronic ones have a cycles per hour setting; the older ones have an anticipator -- which doesn't work as well. I would try with one of the newer ones two cycles per hour at first, and see what that does.

No, it isn't really possible to overvent your mains. A radiator, yes. Mains, no.

The gargling sound you hear on those two convectors almost certainly is condensate which the steam is pushing around. You shouldn't need to change the orifices -- all they are is a hole in a flange or washer, calibrated to the size of the convector and they don't wear out. What you might check is to see if the riser to the convector is still pitched to drain back to the main, or if it might have shifted over time (yeah, I know -- buried in a wall this is a bore, but...).

DAZ_2

Oversized Boiler / Vaporstat Question

I just put a level on top of one of the two convectors, and it is slightly sloped toward the supply side. I assume it should be slightly sloping toward the return side? Is there an easy way to fix this? It appears to be imbedded pretty well in the wall (and not easily moved, if at all), and, of course, it is well attached to the supply and return pipes from below.

gerry gill

sounds to me like

what you need is two stage firing added to the boiler..a vaporstat added without two stage firing will only make it worse.

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DAZ_2

Oversized Boiler / Vaporstat Question

Thanks for the input.

Could you please explain how two stage firing works.

What equipment is needed to put this in place?

Mad Dog_2

Nope...it will just do it more

A Vaporstat on a steam system is what I call a "finishing" device...i.e., The Cherry on the Sundae. You've got much bigger issues with the oversizing. Don't waste good $$$ on a V- Stat UNTIL the other issue is resolved or leave it be. Spend it on beer. Mad Dog

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gerry gill

when pressure starts to build

and reach a certain point the firing rate drops automatically to a lower gas input..like turning down the burner on the stove under a pot of water..once its boiling, its turned down, but still boils..as pressure drops, it automatically re-engages the high fire.

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SpeyFitter

Oversized Boiler / Vaporstat Question

Gerry, is there specific equipment that is recommended to add two-stage firing to my boiler. Obviously, I will need to hire a PRO to do this, but if you are aware of specific brands / models of equipment that are best used for this, I would appreciate it.

Also, with two-stage firing, is the boiler constantly being fired -- either at the lower rate or the higher rate? If so, how does this impact therm usage?

Mad Dog, are you responding to my initial question about whether a Vaporstat will help if the boiler is oversized, or are you responding to the idea of adding two stage firing with the Vaporstat?

Thanks.

Mad Dog_2

I'm sorry...didn't read through the whole post

Mad Dog.

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nicholas bonham-carter

over-fired boiler

i think it would now be the time to determine how over-fired the boiler is by adding up the values for all the rads and comparing that to the rating of the boiler. there seems to be a difference of opinion as to how worthwhile the 2-stage burner is amongst the pros here. maybe an accurate assessment of how much boiler capacity you are trying to under-fire will aid in the final decision. in theory, the hi-lo fire burning should result in lower fuel consumption, even in a correctly sized boiler. there can be problems resulting from the burner tube removal you describe, over the long term, as a result of uneven heating, and its effect on the sections of the boiler.

i am a firm believer in LOW pressures, and very GENEROUS main line air venting, which can only be done, in my opinion, with a vaporstat [assisted by a good low pressure gauge-0-15 oz.] even though you have a short-cycling situation now, the system will work better when it is at its design pressure of a few ounces. removing the air quickly will also improve the short-cycling, even though it is not a cure for over-firing.--nbc

gerry gill

i use mostly the

maxitrol sr-500-1 regulator and use a make on rise vaporstat to trigger it..the boiler only runs when the t-stat calls for heat..same as always..

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SpeyFitter

Oversized Boiler / Vaporstat Question

Can anyone recommend a vent that has the functionality of the Gorton #2, but is not quite as tall or as wide? Some of my current Gorton #1s are in tight spots close to the ceiling or close to beams. I am told the Gorton #2 has four times the capacity of the Gorton #1, so I understand why you are recommending swapping those out -- but the Gorton #2 is 7 inches tall and 3 inches wide, and may not fit in some of the spots where I have the Gorton #1s.

Thanks.

tim smith

Gerry, I question if you can put 2 stage firing on this boiler

unless mfr has tested it for said operation?? Not all burner tubes will entrain air properly at lower gas pressure to the orifice and will produce High CO when running on the lower firing rate. Whoever is going to do this would need to call the boiler mfr and see if it was ever tested for this operation. Just my thoughts, Tim