total EDR x 1.5 = Boiler EDR output?

Brad White_200

That net IBR number should be at least as high as your connected radiation. The piping has already been deducted at that point.

Now, that "1.33" factor was really experiential, pulled out of the air. Early-on, factors of 50% or more were added and which compounded what were already very conservative steam radiator sizing practices. This put steam boiler installers at a disadvantage when hot water was being made more common, so they settled on "1.33" for most steamers.

Here is another way I go about this if in doubt:

I take off the connected steam radiator (as one number, whatever it is).

Then I take off the steam piping, (lengths x diameter, all sizes) feeding those radiators, including mains and run-outs, plus any dry returns. This gives me, using some charts, another "EDR" number.

(I ignore any wet returns, for the steam by then is "spent".)

The piping EDR is compared and added to the "radiator EDR" number. The piping may well be less than 33% of the radiator or it may be more.

(It also is insulated which helps, but does not change the fact that it has to be warmed at least once a day. I tend to assume bare pipe for that warm-up, again, conservative, but even if insulated, it will be cold in the morning. The fact that it stays warmer for the next cycle is a bonus, by which time that factor means a bit less.)

Point being, rather than just assume my "1.33 factor" covers my piping, I may well find that I need more boiler (has not happened), or that if my boiler size is "just this close", I can opt for the smaller selection.

On occasion, I have found 1.2 or 1.25 factor selections for small-footprint, close-coupled steam systems.

Used wisely, this takes the guesswork out of boiler selection. It just takes a bit more time, that is all. And in the end, you <i>know.</i>

Stewy_2

Is that a good way to figure pickup load?

Steamhead (in transit)

Not really

I assume you're talking about a steam boiler- the Net ratings in BTU and EDR already include a 1.33 pickup factor. Unless you have really extensive piping or no pipe insulation, this should be fine. If you lack pipe insulation, adding it is way cheaper than buying and operating a bigger boiler.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Stewy_2

So if I have a total of 330sqft

after adding all my rads, I just need a boiler that is rated a 330 sqft?

Stewy_2

Brad I gotta be honest, Im not following you here.

I understand what your saying but do I have to add up my piping and add that number to the total EDR of the rads to figure out my boiler size?

example- 9 radiators = 320SqFt EDR
9 radiators + piping = 440SqFt EDR

With one would I use to size my boiler 320 or 440? Thank you

Unknown

What Brad is saying

is(using your numbers), connected radiation is 320 sq.ft.
Connected radiation & piping is 440 sq.ft.
Divide this by your radiation, and you`ll know the pick-up factor is actually 1.37%.

Dave

Stewy_2

Ok but, Im still wondering do I go with a boiler rated

at just the enough for the radiators 320 sg ft or the radiators and piping combined 440 sg ft. Steamhead said at the beginning of this post the pick up factor is already figured.

Phil_17

Use the 320

Because the boiler rating already assumes the 33% pickup factor.

The additional math (which yields a 37% factor for your piping) confirms that the "standard" pickup factor is right for your situation. If your math had shown that the pickup factor was 70% then you would want to upsize the boiler to account for that.

Stewy_2

I think got it, just the rads need to be figured.

thank you for your patience.

Brad White_202

Thanks Dave and Phil!

Thanks for covering for me and for stepping in and helping Stewy.

Exactly right, the "radiator plus pipe" exercise just confirms your pick-up factor rather than just assuming that 33% is all you need on top of your radiation.

Now you KNOW. I would go by the radiation as they said.