How long should it take to heat up?

jp741

We have a single pipe, oil fired steam system.  It takes about 15mins or so for the first amount of steam to hit the first radiators. The radiators at the end of the line take forever to even get intial heat.  We jacked up the thermostat and let the system run for about 2hrs and we finally got heat in all the radiators fully across.  We have tilted and change vents, both on the radiators and on the main.  The pressurtrol is set for cut in at .5 and the diff at almost 2.  Is this normal?  Is the boiler too small?  Any suggestions?

Steamhead

If the main vents

are too small or not working, the system will heat slowly. Have these checked first. Other causes can be an under-fired boiler or a boiler with a hole in it.

jpf321

also..

make sure that you size the radiator vents based on radiator size. bigger vents on bigger radiators.and don't use home depot vents, get a name brand like gorton, hofmann or even maid of mist

jp741

Vent size to rad. size

Thanks!  What is the easiest way to determine vent size for each rad.?  Any suggestions for brands on the main line vents?

The Steam Whisperer (Formerly Boilerpro)

My take on vent sizing......

http://www.heatinghelp.com/article/11/Hot-Tech-Tips/1551/Taking-Another-Look-at-Steam-Boiler-Sizing-Methods-by-Dave-Boilerpro-Bunnell



Happy steaming!!

jpf321

vent sizing...

you need to



1) determine what is termed the EDR of each radiator .. Rod probably has a cheat sheet for EDR in his library .. you could also order Dan's EDR book. http://www.heatinghelp.com/products/Books/5/80/E-D-R-Ratings-for-Every-Darn-Radiator-and-convector-youll-probably-ever-see

2) determine the length and size of the pipes leading to each Radiator (the run-out) because pipes hold air as well.

3) You can download the venting and balancing download book available in Dan's shop. http://www.heatinghelp.com/products/Books/5/146/Balancing-Steam-Systems-Using-a-Vent-Capacity-Chart-by-Gerry-Gill-and-Steve-Pajek

4) You can download the venting worksheet available in my signature and work to plug in the numbers EDR, size, runout... the worksheet works best when coupled with the Balancing Book above.



Main vents are normally Hoffman 75, Gorton #1 or Gorton #2 (#2 is the biggest of the 3). To get Gortons online, you need to visit www.pexsupply.com .. Hoffmans may be more commonly available but not as capacious.

jp741

should the main heat first

I would imagine the ideal would be for the main line to heat up first and then distribute to the rads above.  If we get heat in the some radiators before the main line starts venting does that mean the main vents are too small?  Having alot of trouble getting the rads at the end of the line to heat....except on really cold days and the boiler runs for a long time.

BobC

Vents

You want your main to heat up fast, within a couple of minutes of the header. If it takes a lot longer than that you need more venting on the main - you need a bigger vent. Vents are rated in the amount of air they can vent.



A few examples-

Hoffman 4A    0.133 CFM

Hoffman 75    0.500

Gorton #1      0.333

Gorton #2      1.10



How long are your main(s) and what diameter? Ten feet of 2" ID main contains about 0.22CFM (ten feet of 3" ID main is about 0,49CFM). Ideally you want to vent all that air in about a minute because you also have to vent the air in the boiler as well as the header. So for 10 feet of 2" main I would use a Gorton #1. If I had forty feet of 2" main that would contain about 0.88 cubic feet  so I would want a Gorton #1 or two Hoffman 75's.



All the other posts in this thread are right on the money. If you need new vents get them from a plumbing supply house or pexsupply.com.  You might want to pick up some of Dans books available under SHOP so you understand how the system should work.



Also the pressure should be set so it cycles between 0.5 and 1.5 PSI to save fuel. Try moving the white dial inside the pressuretrol down to 1.



good luck,



Bob

jp741

experiment

I tried a little venting experiment as I can't believe how quick the main is supposed to heat.  I closed all the valves and vents on the radiators, then removed the vent off the main line to see how it fast it would vent....it still took a good ten minutes for the steam to make it through.  With oven mitts on I put the vent back on the main and proceeded to find that some of the steam had made it intoa few of the radiators anyways.  I started to slowly open up the radiators one by one starting with the furthest distance....which for the first time I could hear the air escaping from the vents and the steam fill the last rads. with heat.  So do you still think a larger vent would improve the situation when no vent at all didn't seem to help much?

The pigtail has never been do you think that could be part of the issue?



Thank you for all your help!!

BobC

Venting

How big is the threaded hole for the main vent? In the past someone my have decided to use small radiator vents on the main. radiators use 1/8" (about 3/8" OD) instead of the normal 1/2 or 3/4 main vent thread. If they did use the radiator vent the hole is just too small to allow the large pipe to vent properly no matter how many vents you try to add to that hole.



How long are the mains and what is the diameter of the pipe? What vents are on there now and are they in the right place? They should be near the end of the main - about 15" back from where it drops down but after all radiator take offs. Are the mains pitched so the condensing steam can make it's way back to the boiler?



Again pictures of the boiler, the near boiler piping, the mains, and the main vents would make it easier to decipher your problem.



What is your boiler rated for in square feet of steam and what is the connected load (the square footage of all of your radiators)? JPF321's post about determining the EDR is right on the money. You need to identify what style of radiator, how many columns, how many sections on that radiator to know what it's EDR is. You then have to figure out how many feet of what size pipe feed each radiator. The combination of the radiators volume and it's pipe volume will tell you how much venting you need on that radiator.



Ideally the boiler should put out about 20-30% more sq feet of steam than your radiators can use to take into account the piping losses (called pickup factor). All of this is dependent on how well insulated the house is and if you have drafty rooms.



Bob