EDR Calculation

Dave_23

I have a home from the 1920 steam heated, two-pipe vapor system. Over the decades, the house has had all new windows, insulation installed, etc.  As a result, many of my rads don't fully heat top to bottom before the thermostat is satisfied. (I generally run the house at about 68 degrees F)



Whereas, all rad sizes are original to when the house was coal-fired.



So, when calculating EDR for boiler sizing, should the entire size of the rads be used or should the EDR be reduced to reflect the actual percentage of each rad that heats up. It seems intuitive to me that a house with a significantly improved envelope could make due just fine with fewer BTU's.



Thoughts?

Charlie from wmass

use the whole EDR

Unless you change the size of the radiators you need to use the whole size for your boiler choice. Remembr the boilers include the 1.33 in their ratings so do not add it twice.

Dave_23

EDR Calculation

Why include the portions of the rads that never heats in the calculation (close to 50% uniformly thoughout the house)? Seems as though I could replace the rads with some half the original sizes and be just fine, then downfire or downsize the replacement boiler.

Charlie from wmass

The boiler if sized too small

may not get the steam past the first few radiators.

Dave in QCA

There may be an option

What kind of two pipe vapor system is it?  Moline by chance?   Can you take a picture of the valves feeding the radiators and the pipes coming out of the radiator?

Paul48

Just Curious

How does the EDR match up with the size of your current boiler?

Dave_23

Trane system

My system is a Trane Vapor system two pipe system. All returns dry, above the water line then return to the boiler through a single, common drip. The system is quiet and works quite well, except for the undersized rad in the master bedroom (see earlier post)



As to the rads, inlet valves are tapped in at the top of the rad. They are standard, everyday steam valves. Whereas the outlets are low, on the opposite side, and tapped into standard thermostatic traps. Rads are all pitched slightly to the outlet side.



As to venting, I have Gorton #2's on the ends of the each of the two main loops where they drip back into the boiler, and a Gorton #2 at the top of the return drip to vent the return.



In addition to the 30 PSI gauge, I also have a 0 to 10 oz/in gauge and a vaporstat for control. I believe the system truly operates in the vapor mode since I rarely see the 10 oz gauge move and the system always satisfies on temp, not pressure.



The steam flies though the mains once the boiler steams.

Paul48

Savings

Your system has corrected itself to compensate for improvements to the envelope. If the radiators are now twice as large as they need to be, and only heat up half way, you have no problem. As Charlie said....If you try to down-size the boiler, you may have issues with balance. Your savings will come from shorter and less frequent run times.

Dave_23

Rads

Thanks for the tips. I may downsize a couple of the rads that only heat to 50% purely for aesthetic reasons. Boiler size stays the same.

Paul48

Ahhh

A wise decision Grasshopper. :-)

Charlie from wmass

One question Dave

does your dry return get steam hot or just condensate hot?

Dave in QCA

opportunities perhaps

First, let me say that I agree completely with sizing advice that has been offered in this thread so far.  It is 100% correct for conventional 2-pipe systems. 



However.....

If you are near the point of having to replace your boiler and you are certain that your total EDR of your radiators is too large for what you actually need, there may be an option for you to use inlet orifice plates on your radiators.  If you did so, you can size the orifice plates for the EDR that you need in each space instead of the EDR that is actaully present.  Thus, if you set it up to run on 8 oz, and you have an 80 EDR radiator, but only need a 50 EDR radiator in the room, even when the temperature is 20 below zero, then you could put in an orifice plate rated for 50 EDR.  But, you have to put plates on all of the radiators.  You can downsize the whole system in doing so.  In addition, when sizing a boiler for an orifice system, you do not use the pickup allowance, just a 10% piping loss allowance assuming that your pipes are insulated.  That is to say, in an orifice system, you DO NOT match the boiler EDR rating to the total EDR of the system.



Let me know if you have seen some of the articles on orifice systems that are posted on this site.  Henry Gifford has a real good article, but his description is based on 2 psi, and if you have a vapor system you can size at 8 oz as long as you have a vapor stat to control.  If you can't find them, I will hunt them down an post the link in this thread.

Dave_23

Hot returns

There is one spot near an outlet of a convector (not conventional rad) where the return pipe at the point it connects to the dry return loop gets almost too hot to touch. Not sure if it's steam or very hot condensate. My guess is steam. Elsewhere, the dry return is just warm to the touch, so I'm guessing it's mostly due to warm condensate. I don't believe there is an overabundance of steam in the dry return (not supposed to be, is there?), so my sense is that the dry return is handling condensate only. Generally, the system seems to work quite well.

Charlie from wmass

Yes Dave

just condensate in te dry returns. I was asking because traps need maintained. The one that feels hot probably needs repaired.