Steam velocity

HeatingHelp · December 2016

Steam velocity

Raising the pressuretrol setting on a steam heating system isn't going to get the building hotter any faster.

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MAPSteamhead · December 2016

Awesome way to describe / explain the movement of steam! Thanks for your excellent books as well!

DanHolohan · December 2016

Thanks for reading me!

Geezak · January 2018

Hey Dan, you can teach me anything! Great job, easily understood for the layman...very nice job.

Mad Dog_2 · January 2018

I always read & reread Dan's writing and my understanding gets deeper. I would posit that no writer has done more to 'Splain concepts to the average Joe in an Industry, than Mr H. Mad Dog

DanHolohan · January 2018

Thanks, guys!

joeyxf · June 2018

Thanks for the explanation, I've been studying steam for years but never understood a thing until now lol Thanks

EBEBRATT-Ed · June 2018

When I have trouble I always remember the Volkswagen Beatle (my first car) and the school bus. It make me smile. @DanHolohan a great writer and teacher.

DanHolohan · June 2018

Well, thanks!

John732 · April 2019

Awesome visuals , now and then I need to refresh things in my mind and this is a great way to understand it. Awesome

DanHolohan · April 2019

Thanks, @John732

twbrkfd1 · January 2

Pressuretrols were NOT intended to modulate the boiler in a residential install. This is why Vaporstats are needed. The Pressuretrol doesn't work well below 2PSI, and actually is unable to cutout below about 1.5PSI. We don't want to waste energy by running the boiler until it hits the Pressuretrol's low capability to cut off. Old steam residential systems relied on the inherent heat releasing effect of the piping to modulate the boiler, but that means ALL the radiators are on! To get the pressure below 0.5PSI or thereabouts at least 1/2 the radiators MUST be on; wasting heat!

This is why Vaporstats are needed today! Energy cost was not a concern 100 years ago!

Grallert · January 2

This is why Vaporstats are needed today! Energy cost was not a concern 100 years ago! ????

Energy costs were most certainly a concern 100 years ago

Jamie Hall · January 2

https://forum.heatinghelp.com/discussion/comment/1880443#Comment_1880443

Fro many — dare I say most? — residential steam systems pressuretrols are fine. And relatively inexpensive. And even moderately reliable. They can be set to cutout at about 1.7 psig and back in a 00.7 psig and that's just fine.

Some two pipe systems, referred to as "vapour systems" do require lower pressures to operate correctly, and for those a 0 to 16 OUNCE gauge vapourstat or equivalent is required.

Now on modulation. ALL heating systems require modulation. The question is what kind, and where — and that depends very much on the system. In the case we are looking at here, of fuel fired steam boilers connected to radiation (usually radiators) what is needed is to modulate the output of the system as a whole to match the heat load of the structure. That's the job of the thermostat. Then, within the system itself, it is to modulate the power output of the boiler to the power requirement of the radiation. That is the job of the pressuretrol or vapourstat. Contrary to @twbrkfd1 's comment, in fact that is EXACTLY what they are for, and properly installed an adjusted that is what they do.

Now many residential systems — and all commercial systems — will have at least one and usually two other pressure control devices which will shut the system off if the pressure exceeds a safe operating valve. Those are not to be confused with the modulating control.

Steam velocity

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