520 Highboy Specs

In the classified section I have listed for sale an EFM (Fitzgibbon) 520 Highboy In the ad I mention the higher water capacity, larger heat exchange area and the ability to front-mount a DHW coil (up to 7 gpm) as advantages of the Highboy compared to a regular 520. While I believe all of these things are true, different forum members seem to have different beliefs about some of the details. Does anybody have the original specs from which such comparisons could be made? The actual water capacity, and whether the Highboy was originally spec'd with a 7 gpm coil (as were the bigger EFM boilers) seem to be the biggest questions at the moment.

Thanks.

Mike

I was looking through the old registry books yesterday and the only comment about the early boilers was that they included a coil.

A 7 gallon coil should work anywhere a 5 gallon coil is used. It's the same opening and length and thickness.

Thanks very much for checking. I understand that a larger coil will fit in the opening. Maybe there's somebody on the forum who can shed further light on the specification of a 7-GPM coil in the Highboy vs. 5-GPM in the regular 520's.

For what it's worth, I found 1 vote for 74 gallons as the water capacity of the Highboy: (post from 10/16/2008).

Mike

Pacowy wrote:Thanks very much for checking. I understand that a larger coil will fit in the opening. Maybe there's somebody on the forum who can shed further light on the specification of a 7-GPM coil in the Highboy vs. 5-GPM in the regular 520's.

For what it's worth, I found 1 vote for 74 gallons as the water capacity of the Highboy: (post from 10/16/2008).

Mike

5 or 7 GPM coils will fit in all efm boilers 350 520 700 900 1300 The High boy was made from 1948 to 1954 the boiler is 8" higher then a standard AP-520 and holds 54 gals of water not 74 gals the 700 holds 74 gals . Highboy has the coil up front along with a bigger ash door lip sticking out . 900 hold 94 gals of water 1300 120 gals . The difference in a 5 to a 7 gal
coil is 2 extra 1/2 " finned copper loops both are 29" long The standard 520 hold 40 to 41 gals of water depending on manufacturer. What else wold you like to know about them .

coal berner -

Thanks very much for the info.

I do have another question. On the spec sheets I've seen, the 700, 900 and 1300 are always spec'd with the 7-gallon coil, while the 520 is spec'd with the 5-gallon coil. Do you (or does anybody) know how the Highboy was spec'd? If both coils fit in the same opening, why are the bigger units spec'd with the bigger coils? Does the bigger coil not perform the same in the smaller boiler? Or do they figure that the bigger units are more likely to be used in situations where the water demand is higher (e.g., multi-unit building)? Or maybe there's some other reason?

Mike

In order for a 7 gallon coil to actually produce a constant 7 gallons per minute, you need the ability to make enough heated boiler water which surrounds the coil. Even a 5 gallon coil will not produce 5 gpm unless the burner is able to keep the boiler water hot enough. Throw in other factors such as the heat load of the building and it affects the coil output even more.

So, if I follow what you're saying, for a 7-gallon coil to sustain that output, the boiler water needs to absorb something like:

7 gpm x 8.33 lb/gal x 60 min/hr x 80 deg rise [assumes 45 deg in, 125 deg out] x 1 btu/(deg rise x lb) = 279,888 btu/hr.

That's higher than the gross output of an S-20 (let alone the part that makes it into the boiler water), so a 520 generally wouldn't be able to sustain 7 gpm dhw output, while the bigger EFM's probably could. A 7 gpm coil in a Highboy might initially be able to put out more dhw than would a 7 gpm coil in a regular 520 due to the BTU's in the Highboy's higher water volume, but in the longer term it, too would have difficulty keeping up.

Is this a fair summary?

Mike

I have the formula at work.

Take a look at my topic on piping and circulator selection:

Yanche's Toolbox, Piping & Circulator Selection Method

The equation you need is the heat flow equation,
Buy looking at my overall analysis you can make the drawn down flow rate assumptions that apply to your installation and your boiler water temperatures. You will need to make some assumptions about the domestic coils heat transfer capability. I'd search for technical specs published by manufactures of similar coils or products. If you do some analysis kindly post you results for all to see.

Thanks. I think that's the same as the formula I used. 8.33 x 60 = 499.8 [pretty close to 500], so mine is also basically 500 x flow rate x temp diff = 500 x 7 x 80 = 280,000 btu/hr. Is 80 a fair number for the temp diff? Around here the cold water that comes out of the pipe is numbing - especially in winter - but I've never taken its temp.

Mike