Replacement boiler sizing

HeatJockey

As per Dan's: "Some days the desire to oversize a boiler is stronger than the desire for sex"...    Replacing a old HB Smith 25 mills 6 section boiler (1600 sq ft steam)   Existing installed radiation only measures 503 sq. ft.      2 stores on the ground fl have been disconnected however the supply piping is still there serving 14 small radiators on the upper floors.   Do I trust the new boiler rating of 540 sq ft or do I need to go up a size due to the large supply pipe sizing in basement?   Also, just to throw something else into the mix: Is there any difference in boiler quality or steam supply if the boiler risers requirement is 1 @ 3" or 2 @ 2"?  Thank You

Greg Maxwell

Boiler replacement

I have run into this situation before, and it can leave you scratching your head for the correct answer.

First, are the disconnected stores ever going to be reconnected? That is the million dollar question. If so, you have to calculate that load into the replacement boiler. If not, then I would size to the existing load, then add for pick up and piping loss of about 15%, That would leave you with needing approx 600sq'. Also, insulate those mains, and check all vents or traps.

As far as the risers go, I always would go with a boiler with 2 risers, keeping the exit velocity low, and avoiding the possibility of a tipped water line.

Hope this helps. 

HeatJockey

Thank You

Going up a size is more comfortable than cutting it close with a good customer. Reassurance from someone else stops the "am I being an idiot" feeling.

Paul_11

boiler sizing

Have you done a heat loss? Even a quick heat loss calculation will help as well.

You dont' have to heat up the entire radiator if the radiator is larger than you need.

Quite often I go smaller than the connected load if the heat loss is much smaller than the connected load.

If the heat loss is larger than the connected load you go larger and plan on adding radiators.

You do always have to take into account that the supply steam piping was sized for all of the original radiators.

Good Luck

Paul

Charlie from wmass

The boiler with one 3"

has the lower steam velocity. You can figure the area of a circle. one 3" is larger than 2 -2" circles. & point odds to 6 point odds so a 15% increase in volume on the pipe. Roughly.

The 3" requires big wrenches, threaders and more sweat. the 2" is easier for the light duty shop and is almost large enough to do the job. Now 2 - 21/2" risers is better than one 3" riser.

Greg Maxwell

boiler sizing

Thats interesting on the area of a circle. I didnt know that, thanks for the info.

As far as diong a heat loss for that job, with a steam system, I would still size for the connected rads, but then use adjustable vent valves to adjust each rad.

Paul_11

do we always need to fill the radiators with steam?

That will certianly provide adequate heat, but you will be oversizing the boilers more times than you think.

For the simple reason that the steam system was oversized to begin with because of the foul air issue. The original radiators may have been oversized by 30%. See page 71 in Lost Art.

Varivents will shut down the boiler and prevent overheating, but you may get short cycling on certain jobs.

On small buildings, this does not matter that much.

On bigger building it matters a lot.

Right now I'm extimating a job where the engineer specified a 6,000,000 BTU boiler when a 4,000,000 will do just fine.

Can you imagine the cost difference on this job?



Paul

Greg Maxwell

Boiler replacement

I have been on those "engineered" jobs as well. Ultimately though, the rads will still need to be filled, and the amount of steam they will need to be filled with will be the job of the vent. We are not talking about a grossly oversized boiler here, such as the one you mentioned, but you have to remember, there are grossly oversized mains and run outs, which still need to be filled with steam. I would still be careful choosing the boiler, keeping piping in mind that even though you take the sq', and then add 15% for a piping loss, you still have to compensate for that main size.

Charlie from wmass

Paul the correct answer is no we do not need to

fill every radiator to heat the building properly on most days. We need to fill every radiator on design days. Also remember if the radiators are in rooms below 70 degrees they will call for more steam to heat across as the effective square footage per section increases the lower the room temp gets. Customers will also find that radiator that does not warm across and call you out on it even if the fuel bill drops and the building is perfectly comfortable.

HeatJockey

Varivents

A vents job is to allow air out of the system so that steam can enter the radiator. Varivents are adjustable to allow balancing of the system. Any vent won't close until steam fills the radiator. You would have to be really, really good and invest a lot of time to balance a system room by room ( by room temperature not radiators getting hot) with only partially filled radiators.

STEAM DOCTOR

varivents

Varivents are absolute junk. They have an incredibly short lifespan. If there is the smallest issue with water in the system they will spit like crazy. They vent much to fast. Get Gerry Gills venting book available on this site. Worth its weight in gold. Balancing is not hard if done right

crash2009

How come I never win in Vegas?

I'm not really good, I invested a lot of time, and I did balance my one-pipe room by room, with only partially filled radiators.  This building is the same temperature from top to bottom.  Including the boiler room.  All I did was pipe the boiler correctly, clean the boiler water, insulate/slope and vent the mains properly, and match the vent to the EDR of the radiator.  Gorton D for 30-40 EDR, Gorton C for 20-30 EDR, Ventrite #1 for the smaller rads, and the stacked rads (2 rads one riser).  I found that Steve and Gerrys Balancing Steam Systems was very much worth the 10 bucks.  Oh yea, one more thing, less venting on the 1st riser and more on the last.

Thinking back on it, it was a lot of work, but it sure is worth it.



Thank-you Heatinghelp!