Boiler Sizing....EDR vs. DOE Btu Rating???

AdmiralYoda

I've got a quick question on the differences between sizing a boiler by EDR vs. the DOE btu rating.

I have an EDR of 250. The pipes are well insulated with 1" fiberglass, including the near boiler piping with is done correctly and is also well insulated. Two 2" risers to a 2" drop header and 1.5" equalizer. Each main has more than enough venting. Two Big-mouths on each main, probably overkill and one would probably have been fine. It is a single pipe counterflow system.

The two boilers I am considering are the Weil-McLain EG30 and the Peerless 63-03L.

Note: To calculate the btu's needed instead of EDR I am just multiplying the EDR by 240. So 250 * 240 is 60k btu.

EG30: 196sq.ft. of steam, 62k DOE output Btu
- Based on EDR, I would be 31.6% undersized. (196sq.ft. / 250sq.ft.)
- Based on DOE btu output, I would be 3% oversized. (62k btu / 60k btu)

63-03L: 233 sq.ft. of steam, 74k DOE output Btu
- Based on EDR, I would be 6.8% undersized. (233sq.ft. / 250sq.ft.)
- Based on DOE btu output, I would be 23.3% oversized. (74k btu / 60k btu)

Using just EDR , the 63-03L seems like the best option. 6.8% undersized on a well balanced, insulated, vented system. Using just DOE btu, the EG30 seems like the best option. 3% oversized based on btu alone.

Which is the best way? The goal here is efficiency and fuel savings. I usually keep the thermostat set at 68 but it would be good to be able to use a 2 degree setback if I ever wanted.

What do you experts think? Thanks in advance!

ethicalpaul

I think there will be no noticeable difference in efficiency or fuel usage (your stated goals) between these two. I would look to other decision factors.

ChrisJ

AdmiralYoda said:

I've got a quick question on the differences between sizing a boiler by EDR vs. the DOE btu rating.

I have an EDR of 250. The pipes are well insulated with 1" fiberglass, including the near boiler piping with is done correctly and is also well insulated. Two 2" risers to a 2" drop header and 1.5" equalizer. Each main has more than enough venting. Two Big-mouths on each main, probably overkill and one would probably have been fine. It is a single pipe counterflow system.

The two boilers I am considering are the Weil-McLain EG30 and the Peerless 63-03L.

Note: To calculate the btu's needed instead of EDR I am just multiplying the EDR by 240. So 250 * 240 is 60k btu.

EG30: 196sq.ft. of steam, 62k DOE output Btu
- Based on EDR, I would be 31.6% undersized. (196sq.ft. / 250sq.ft.)
- Based on DOE btu output, I would be 3% oversized. (62k btu / 60k btu)

63-03L: 233 sq.ft. of steam, 74k DOE output Btu
- Based on EDR, I would be 6.8% undersized. (233sq.ft. / 250sq.ft.)
- Based on DOE btu output, I would be 23.3% oversized. (74k btu / 60k btu)

Using just EDR , the 63-03L seems like the best option. 6.8% undersized on a well balanced, insulated, vented system. Using just DOE btu, the EG30 seems like the best option. 3% oversized based on btu alone.

Which is the best way? The goal here is efficiency and fuel savings. I usually keep the thermostat set at 68 but it would be good to be able to use a 2 degree setback if I ever wanted.

What do you experts think? Thanks in advance!

Well.

I see 60,000 DOE output as being dead on for your system.
15% over would be 69,000.

The 74K is a bit much in my opinion but would work fine.
The 62K is a bit light, but could likely be tuned to work well but may take more effort.

I certainly don't consider the 74K to be undersized at all.

How is the piping? Is everything piped correctly or are there short cuts? 90's into the top of the main etc> What are you using for vents? Have you calculated actual piping losses?

AdmiralYoda

@ethicalpaul true, but my question is really the difference in sizing a boiler by EDR or DOE Btu's. Normally EDR is used and that would mean the EG30 would be 31.6% undersized....which most people would not want. Based on BTU's it is 3% oversized....which most people might be happy with.

Which is the best way to calculate ideal boiler size? DOE output BTU's or EDR?

@ChrisJ 1" insulation on everything, near boiler piping exceeds the minimum requirements in the manual. Two Big-Mouths at the end of each main. I have not calculated my piping losses, no.

Jamie Hall

The difference between EDR sizing and DOE BTUh net output sizing is the pickup factor -- which is in the EDR calculation and NOT in the DOE BTUh net output. So in your situation, with good insulation, you don't want to go over the EDR size, since you don't need to go with the full pickup factor (usually 33%). But you do need some, and in my humble opinion the 63-03L is the better option.

AdmiralYoda

@Jamie Hall Thank you! So in otherwords.....the 63-03L would be perfectly sized, but with a 24% pickup factor instead of 33%.

If the system is very well balanced, insulated and piped correctly...what is a reasonable minimum pickup factor? I hear on here that 33% is often too high and some people use 25% or lower.

ChrisJ

AdmiralYoda said:

@Jamie Hall Thank you! So in otherwords.....the 63-03L would be perfectly sized, but with a 24% pickup factor instead of 33%. If the system is very well balanced, insulated and piped correctly...what is a reasonable minimum pickup factor? I hear on here that 33% is often too high and some people use 25% or lower.

I feel 0% is the minimum.

I'm running around 10% and it's wonderful.  That's simply because it's as low as this boiler goes with stock settings.

I can do all of the setbacks and recoveries I want and never build pressure or listen to hissing vents.

pedmec

just so everybody is on the same page, how did you come up with 250 EDR? you did get it from the radiators, correct? just checking.

EBEBRATT-Ed

The EG30 would be too small. Use the Peerless. Your forgetting the pic up factor which is 33%

ChrisJ

EBEBRATT-Ed said:

The EG30 would be too small. Use the Peerless. Your forgetting the pic up factor which is 33%

He didn't forget the pickup factor.

The Steam Whisperer

If this is 2 pipe steam, with a little radiator work, you should be able to go down to the current design heatloss and ignore the EDR rating limitations. One pipe steam, you're safer using the EDR sizing method with a small pick up. 250 EDR can heat 3000 sq ft of typical reasonably insulated detached single family home at a design temp of about 0F outdoor

AdmiralYoda

Thank you everyone! For EDR I measured the size and used one of the many available charts per the type of radiators I have. All of my radiators are the old thick tubular type and I have one column type. The house was built in the late 1880's and it wouldn't surprise me if the radiators are original to the house.

My calculated EDR is actually 219, but I'm adding a small radiator to a cold corner of a living room (EDR about 10ish) and a radiator in an a new bedroom (EDR of 20). So I'm calling it 250, although it could be +/- a couple.

It is a single pipe, counterflow setup. The house had no insulation except for some R13 in the attic and had old drafty windows and doors when we moved in. The existing EDR heated the house just fine then, even with all the pipes being uninsulated and using an excessive setback overnight.

Now the house is fairly well insulated, has decent windows and doors and the pipes are insulated with 1" fiberglass. The house is only 1700 square feet and if I felt like doing a heat loss calculation of the house, I could probably get away with a lot less EDR.

ChrisJ

If it was mine I'd go EG30.


But.
I'd also have no problem spending months tuning it and messing with things.

ethicalpaul

AdmiralYoda said:

@ethicalpaul true, but my question is really the difference in sizing a boiler by EDR or DOE Btu's.

I can only go by what people say

Which is the best way? The goal here is efficiency and fuel savings.

I'd go with EDR. I sure like my Peerless

Tim_D

With a steam system you must always select a boiler that produces enough steam to fill the system meaning that you need to select a boiler that provides the correct sqft of steam. The EG-35 provides 258 sqft of steam. Never use the DOE rating to select a boiler. Always use the Net rating. The difference between the DOE(gross output) and Net is the pick up factor. When you calculate EDR it does not include allowance for the losses through the piping. The pick up factor covers this. DOE is simply input x efficiency. Selecting a boiler based on DOE almost certainly ensures insufficient heat on the coldest days of the year.

Jamie Hall

The objective of the exercise, @AdmiralYoda , is to get the boiler power output -- however measured--to match as closely as possible the system demand. If it is oversized, it will cycle on pressure; how long it takes to build pressure and get there depends on how oversized it is, but also on venting. If it is undersized, you may -- or may not -- get satisfactory heat from all of the radiation.

It might help to think of it in a completely different way. Consider a car on a level road, standing still. Let's suppose you want to travel at 60 mph rather than just sitting there. You must use more accelerator to get up to speed than it takes to maintain speed. If you use just a little bit more, it's going to take a while. If you floor it, it won't take long. If you don't use enough, though, you'll never get there. That little bit more is analogous to the "pickup factor" in steam which we often talk about, and how much is enough is open to debate. A pickup factor of 33% is built into the boiler EDR rating. With a well insulated and vented piping system, it's more than is really needed, but how much more is a good question.

Will having an oversized boiler affect efficiency? A little. There's a pretty good debate going on that one, too. If the boiler cycles on pressure all the time, yes you are taking a hit. If it only cycles on pressure after a very long run -- say out of a deep setback or on a design day -- say a 45 minute to an hour -- then no, you're not losing anything. You're fine.

If doesn't matter whether you use the EDR figure of DOE output rating to do the sizing, as long as in either case you match the radiation and, in the case of DOE output, do your math right.

The Steam Whisperer

Tim_D said:

With a steam system you must always select a boiler that produces enough steam to fill the system meaning that you need to select a boiler that provides the correct sqft of steam. The EG-35 provides 258 sqft of steam. Never use the DOE rating to select a boiler. Always use the Net rating. The difference between the DOE(gross output) and Net is the pick up factor. When you calculate EDR it does not include allowance for the losses through the piping. The pick up factor covers this. DOE is simply input x efficiency. Selecting a boiler based on DOE almost certainly ensures insufficient heat on the coldest days of the year.

This is not true when sizing boilers for supply valve orifice systems (mainly a subset of two pipe systems). The Moline is one of several examples. These boilers can be sized to the heat loss of the building in every instance we've encountered or in the systems we have modified with orifices. Many of these systems also utilize direct outdoor reset of the burner capacity, with the burner modulating down to low fire usually around 40F outdoor and then gradually modulating up to high fire at outdoor design temperature. Some larger multiunit buildings buildings have closely monitored the boiler after these installations and saw the boiler firing continuously for weeks on end with very stable and even indoor temperatures. Some examples:
+2,800,000 input on/off boiler that now modulates from about 400,000 in warm weather to 1,200,000 at design temperature. A recent check of the temperature averaging control showed only a 0.2 F difference between the 6 snesors in 6 different units.
+ 1260,000 input on/off and now mods from about 300,000 in warm weather to 630,000 at design.
+Church with 2,100,000 input boiler now has 2 step fired 350,000 btu/hr boilers and 1- 150,00 input water boiler. A single 350,000 input boiler heats all 15,000 sq ft on design day.

All of these jobs have seen 25% to 50% reductions in fuel usage.

ChrisJ

ethicalpaul said:

@ethicalpaul true, but my question is really the difference in sizing a boiler by EDR or DOE Btu's.

I can only go by what people say

Which is the best way? The goal here is efficiency and fuel savings.

I'd go with EDR. I sure like my Peerless

I'll see that and match you with, I sure like my WM EG series.

  

captainco

The DOE rating is based solely on a bogus combustion efficiency calculation. The net IBR or net AHRI rating is just a fixed deduction from the DOE rating, but neither is a actual measured delivery. You are better to use the lower rating when sizing the boiler.
Because I had friends at the testing and certifying labs, I was given this information off the record.

ChrisJ

captainco said:

The DOE rating is based solely on a bogus combustion efficiency calculation. The net IBR or net AHRI rating is just a fixed deduction from the DOE rating, but neither is a actual measured delivery. You are better to use the lower rating when sizing the boiler.
Because I had friends at the testing and certifying labs, I was given this information off the record.

When I had a combustion analysis done and it said the efficiency was 84.9% at that time, was that bogus?

The Steam Whisperer

The other thing to watch out for is that the boiler cannot provide the gross rating because the cycleguard shuts down the boiler periodically during continuous heat call. The loss in capacity ranges from about 7 to 10%.

Jamie Hall

@The Steam Whisperer 's comment is quite correct: with one very important proviso. that is, the orifice sizes (or in the case of variable valves such as Hoffman or Dunham) the sizing is done for the heat wanted in the space, not the size of the radiation in the space. The effect will be that the radiation -- no matter how large it may be -- will only heat to a limited degree.

If the radiation is significantly oversized with relation to the heat load of the space -- as is often the case when it has been possible to perform significant heat loss upgrades -- the results may be satisfactory. One does have to wonder if the resulting reductions in energy usage are due to the undersizing and orifices -- or due to the reduction in building heat load.

captainco

ChrisJ - Absolutely bogus! Non-condensing automatically deducts 14%. O2 = 1% per 1%/
6% O2 = 6% loss
Flue temp = 1% loss for every 30 degrees higher than combustion air temperature. Assume a 370 degree gross flue temp. Combustion air = 70 degrees 370 minus 70= 300 degrees divided by 30 = 10%
Analyzer may show 80+ but this is only 70%

The Steam Whisperer

Jamie Hall said:

@The Steam Whisperer 's comment is quite correct: with one very important proviso. that is, the orifice sizes (or in the case of variable valves such as Hoffman or Dunham) the sizing is done for the heat wanted in the space, not the size of the radiation in the space. The effect will be that the radiation -- no matter how large it may be -- will only heat to a limited degree.

If the radiation is significantly oversized with relation to the heat load of the space -- as is often the case when it has been possible to perform significant heat loss upgrades -- the results may be satisfactory. One does have to wonder if the resulting reductions in energy usage are due to the undersizing and orifices -- or due to the reduction in building heat load.

We have found a regular pattern that nearly all radiation installed between about 1905 and 1941 is 60% oversized for the load in buildings that have not had any improvements to reduce heat loss. About the only possible exception I have found is a large church that had radiation around double the heat loss. This system was originally a mechanical vacuum system and was probably designed for very quick recovery after set back. Also, it may have been designed to old SBI standards, which calculated much larger radiators. When you start adding in heat loss reductions due to improvements, existing radiators could be approaching double that needed to heat the building.

Another thing not so obvious is that the pick up factor is basically eliminated and adding roughly 10% to 15 for piping loss to a basement and in exterior walls is all you typically need if you haven't included the heat loss of those spaces.

Tim_D

You have to produce enough steam to fill the radiators no matter what has been done to improve building efficiency.

ChrisJ

Tim_D said:

You have to produce enough steam to fill the radiators no matter what has been done to improve building efficiency.

Why?

Why fill them if it's not needed?

Jamie Hall

The trick is that if you aren't going to essentially fill the radiators, you have to arrange things with orifices or graduated valves -- or more crudely vent adjustments, so that you still get the even heating you want with either longer or shorter runs. Not that it can't be done, it can, but it takes a good deal more fiddling.

ChrisJ

Jamie Hall said:

The trick is that if you aren't going to essentially fill the radiators, you have to arrange things with orifices or graduated valves -- or more crudely vent adjustments, so that you still get the even heating you want with either longer or shorter runs. Not that it can't be done, it can, but it takes a good deal more fiddling.

Works wonderful here.

The Steam Whisperer

Tim_D said:

You have to produce enough steam to fill the radiators no matter what has been done to improve building efficiency.

This is not true with orificed type systems such as the Moline, later Dunham and other really big name systems or any system upgraded with orifices.

We have found that with sizing the orifices based on a fixed percentage of the existing radiation capacity at the peak design pressure, there really isn't much fiddling. WE compare the overall radiation capacity of the building to the heat loss to end up with the percentage of radiation needed to heat on the design day. This percentage is usually about 60%. Then we size the boiler(s) to this capacity plus some extra for piping losses. On larger buildings we modulate the boiler capacity directly with the outdoor temperature, or stage on multiple steam boilers based on the building temperature with a multistage type thermostat. We figure about 2 to 3 % of the installed orifices need to be fiddled with after the initial installation. Also, we check out any replaced radiator to see if we need to make adjustments to keep the heating capacity even.
We usually end up installing slightly over 1/2 the capacity of the current boiler, though sometimes it is much smaller.

The orifices only allow the boiler to "see" the smaller percentage of the radiators, so heating is not a problem. Some systems need a higher fire start in warmer weather when the boiler is cycling on and off on low fire. Most of our modulating setups are running about 30% of peak load firing rate in warmer weather and then ramp up as the temperature gets colder.

We have dozens of these systems we've done here in the Chicago area and there are hundreds, if not thousands in New York City.
There is a strong reason why orifice plate upgrades to two pipe systems are listed as one of the most effective methods of reducing fuel usage in steam systems in recent publications by New York City.

ChrisJ

The interesting thing is slow air vents on a single pipe system do basically the same thing as orifices when you mix them with faster vents on other radiators.
 

You can't just put slow vents on everything, but putting G6s and GCs on some causes G4s to be incredibly restrictive on radiators that overheat or steal steam early on.