Vaporstat Setting

Leaky · December 2009

So I just finally installed a vaporstat (yea!) and now am wondering about setting recommendations. Initially I set the cut out at 8 oz, sub. diff @ 6 oz. The boiler would cycle on and off on pressure during a heat call,i.e: acheive pressure and then off for about 1min 20 sec, on for about 1min40 sec. Thinking this represented short cycling I set the vaporstat to 11oz, sub. diff@ 10 oz. The cycles are now a bit longer, but I was hoping to run a low pressure.

Our system has only 5 radiators, one-pipe steam. The boiler is a Peerless 3 section.

What would you recommend setting the vaporstat at and why? Thank you!

Steamhead · December 2009

Might be time

to have the burner down-fired slightly. Which Peerless do you have, and what burner is on it?

DavidK_2 · December 2009

are you radiators all hot

when the vapourstat switches on high pressure?

I'm no expert, just learning, but my understanding is until all the radiator vents have closed there should not be much pressure in the system. Just enough to drive the steam down the pipes (probably only a few ounces). If your presuretol (vapourstat) is triggering on high pressure before the radiators are hot, you might need more venting.

If all the radiators are hot, then you are probably making more steam than your radiators can condense and steamhead's suggestion for downfiring makes good sense. Again, I'm just learning, but think in an ideal system the radiators will condense steam as fast as the boiler makes it.

Jamie Hall · December 2009

DavidK

may be no expert -- but he's got it. That's exactly what is supposed to happen once all the radiators are hot -- if there is enough venting. So... check your venting first (main vents -- hard to have too much!) and then take a look at Steamhead's suggestion.

Leaky · December 2009

Thanks everyone

If I understand correctly, the vaporstat should almost never cut out the boiler if all the radiators are condensing at a rate equal to the boilers production of steam. Is this true?

Indeed, this would mean I have a need of downfiring. First I'll take a closer look at the venting situation, then revisit the issue if necessary. The more venting the better.

BOILER IS: Peerless WBV-03-110-SPT Nozzle .75 80*nf #20 (what the oil man wrote)

What amount of time should exist between boiler "firing" cycles during a heat call, in your humble opinions??

Jamie Hall · December 2009

Well, almost

During a normal, reasonably average day you are quite correct -- the thermostat and the vaporstat will arrive at the conclusion to shut the system down pretty much together. However, recovering from a deep setback, or a particularly cold day will see the vaporstat controlling the system, even though all the radiators are full. Remember that the boiler is sized for the radiation plus a pickup factor, so this is reasonable.

It is hard to give a hard and fast rule about how the on/off times for a system running with full radiators and the vaporstat controlling, but typically a minute or so off time and a somewhat longer on time might be expected. But it varies so much...

Vaporstat Setting

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