down firing question

Dave in QCA

I am working with a property that has a 2 year old EGH-125. It is connected to a Moline system, which is by definition, fully orificed. The boiler fires at 495,000 BTU and ideally we would be firing at 299,000 to 334,000 BTU, assuming 82% efficiency.

My question, mainly to the pros on here, is to what extent can the current issue of the EGH (with baffles) be downfired? I was under the impression, that the old issue, the EGH-12 without baffles, would lose a great deal of efficiency if the firing rate was turned down. But, then WM down fired the boiler, added baffles, and increased the efficiency by a point or 2. Any insight would be greatly appreciated.

mikeg2015

Where do the original contractor go that oversized it? Let me guess, they got their check.

I think best bed is put on a combustion analyses and see. My limited experiment in my home was losing 1% effeciency downfiring by 30%.

So question is, standby losses by firing efficiency. In my case it was causing noise at the vents.

gerry gill

when i downfire its to make a boiler behave itself on whatever system it is installed on. So my thoughts are never on the efficiency angle but the system performance angle. My feeling is just because a boiler is operating efficiently doesn't mean it is operating well (no hammering, speedy delivery, short cycling etc.).
Just my two cents

Jamie Hall

Amen, brother Gerry -- too often people look only at the boiler for efficiency, but it's the whole system that needs to be considered.

Dave in QCA

@mikeg2015 The contractor installed the boiler about 2 years ago, then the house sold. New owners complain about uneven heating, cold rooms, hot rooms, occasional banging on a few radiators toward the end of very long cycles (20 below zero weather). According to the obvious, the boiler rated EDR is 1193 and the total EDR in the house is 1162. BUT, it's a Moline system. That is a 2-pipe system without traps. It uses orficed valves and low pressures, 6 oz, to meter steam into the radiators in a way that all steam is condensed and no steam gets into the return lines. But.... that means you cannot include a pickup allowance. And, on this boiler, for some reason, Weil McLain has a piping loss and pickup allowance of MORE than 34% Don't know why. Additional considerations that factor into proper sizing, is that we normally think of 1 EDR emitting 240 BTU/Hr on steam. But, that is at 2Psi. Since an orificed system has zero Psi in the radiators, which means that the emission is 225 BTU per sq ft, instead. It all ads up to create a less than desirable situation. To bad the last installer didn't use a EG-75 instead.
@gerry gill Thank you for your input. Your experience and opinions are worth more than I can express.
@Jamie Hall . Thank also sir. You speak to my heart, as I was thinking exactly the same thing. I also know that my old Pennco boiler lost an incredible amount of efficiency when turned down and while it served a necessary purpose, on this one, I just needed a little reassurance.
Thank you all.

mikeg2015

I agree with Gerry. That’s the reason I downfired my boiler. I went as far as to block 2 out of 10 orifices, but in the end I could get away with a 2 stage valve to fire at 1.7” on low and 3.0” on high, so only lightly downfired on high, but 30% less on low.

Blocking orifices cost me 2%. Low fire 1% on top of that. But I’m only getting 75% effeciency right now. Ugh.

Sounds like your system might be happiest with a very slightly undersized boiler even. But someone like Gerry might know best.

mikeg2015

Side note. You mention 240btu/sqft at 2psi. That’s a great point. Most systems are at 0.5-1 psi here so 230-235 is a better number and those of us with vapor system, it’s 225 as you mentioned. Doesn’t sound like much but it’s 10% difference. So a 300k boiler might become 250k on a vapor system after you add pickup.