EDR Between Two Boiler Sizes - Which to Use?

JSR

We are replacing an old Hydrotherm gas steam boiler rated at 603 sq. ft. steam. Using Dan's EDR book, I calculate the connected EDR at 506.5 sq. ft. steam. I have found a very knowledgeable steam contractor who has been to several of Dan's seminars. We walked through the house together and discussed how to size each radiator and the cast iron baseboard. When I got his proposal, he used an EDR of 478 sq. ft. and recommended the Burnham IN6, which is rated for 450 sq. ft. steam. I am not sure why we differ on the EDR. I suspect it is an arithmetic error or such. I have been over my calculations several times and am confident that 506 is the correct EDR. (Another contractor recommended a New Yorker boiler rated at 533 sq. ft. steam.)

The Burnham IN6 is rated for 450 sq. ft. and the IN7 is rated at 542 sq. ft. steam. Assuming the 506 EDR number is correct, do I go with the IN6, which is about 11% undersized or the IN7, which is about 7% oversized? . I am leaning toward the IN7. I would appreciate any insight anyone has to offer. Thanks.

Jeff

BobC

Understand that the sq ft rating on a steam boiler includes a 33% pickup factor for the pipes and many feel that is a bit much if the piping is reasonable (no mains in crawl spaces etc) and it is insulated. The steam mains have to be well vented and all piping has to be the right size and have the required slope..

As an example - a boiler rated at 600sq ft of steam will actually make 800 sq ft of steam and if you do actually have 600 sq ft of connected EDR and your piping is reasonable that boiler could well be oversized for the building.

Ask him for his reasons for selecting the size he did and if he will guarantee the boiler will heat the house on the coldest day. Ask him to email pictures of some of his work and post them here if you can so we can check them for correctness.

Bob

KC_Jones

If you want to start getting into the pickup factor you really need to start with the raw numbers. So for the Burnham with a built in pickup of 33% the "raw" square footage of the IN6 is 598 so using that against your 506 number it gives you 18% pickup instead of 33%. The IN7 would be 718 against your 506 which is a pick up factor of almost 42%. If it was me I would use the smaller one, and you have a pro saying the same thing. As long as your pipes are insulated like they should be this honestly should be a none issue. Keep in mind you only need to fill those rads on the coldest day of the year, the rest of the time you don't. The boiler size is calculated on filling the rads entirely. Also if your radiation is oversized like many are, you may never fill those rads completely.

ChrisJ

As KC said, the IN6 is technically 18% oversized for the radiation and will work beautifully. Do not use an IN7, it will be grossly oversized.


Above all else, please make sure he's going to pipe it properly and by properly I don't mean bare minimum. Two 2" risers into a 3" or even a 4" drop header would be preferred.

STEAM DOCTOR

Burnham only requires a single 2" riser and 2" header for the IN6. Grossly inadequate. If you go with the IN6, insist on two 2" risers and 3" header.

Fred

Tell us more about your system. How many mains? what size? How long and what diameter? Are they well insulated? with what kind of insulation? (old Asbestos or 1/2" , 1" or more fiberglass insulation) , Have you made upgrades to the structure? Whole house insulation? New thermal pane windows? Other envelope improvements? Are any of the mains/radiator run outs in unconditioned crawl spaces?
None of us can really second guess either of these installers (IF THEY ARE BOTH QUALIFIED STEAM PROS AND HAVE BEEN ON-SITE) AND THAT'S A BIG "IF" but I would be inclined to ask each of them why they sized the boiler the way they did and see if they each give you a reasonable explanation and one that allows you to make a more educated decision. Either of those boilers will likely work, I am a bit more skeptical of a pick-up factor of anything less than 20% but that is just my bias. Others have had good performance at even less than the 18% you will have with the IN6. Certainly the IN7 can be down fired to get you to a 30% pick up factor if that is what you decide to do, after hearing the installer's perspective. You can even consider a two stage gas valve on the IN7 as another option to lower the boiler output.
I would suggest:
1) resolve the differences between your EDR numbers and those of the Installers so that you know what you really have.
2) Understand the reasons each installer sized the proposed boiler the way they did.
3) If you decide you continue to have concerns with the size of the IN6 and the IN7, ask those installers what other options (Brands) they install and if one of those options comes closer to what you will be comfortable with.
4) Ask each to give you a written guarantee that their proposed boiler will meet design day standards and see how they respond.
5) Ask about a two stage gas valve on the IN7 and see how they respond, Pros and Cons, if any.
Just my opinion, here. This has been a hot topic for a long time but at the end of the day, you, the OP get one chance every 20 or 30 years to make a good decision. Arm yourself with as many facts as you can gather and make sure your decision is based on an accurate EDR survey. Others will offer up opinions as well. Keep us posted on your new install!

ChrisJ

@Fred

Downfiring an atmospheric boiler lowers it's efficiency and the more you do it, the lower it gets. I would never recommend someone buy an oversized boiler just to downfire it.

The types of windows in the home and insulation are irrelevant to this discussion as we're trying to drive a load "the radiators" and that load is a certain size.

If you're concerned about heatloss you're looking for the hot water section.


You do make a good point on pipe insulation, but he'll have what, 22,000 btu's worth of piping factor? I'm sure that's more than enough.

Fred

@ChrisJ
I don't want to take this thread off topic for this OP. My interest in understanding the OP's environment is more to understand how "Loose" or "tight" his envelope is and if that might affect how often the boiler might cycle, which certainly may affect the Pick-up/Piping load, at least in my opinion.
I stand by the suggestions I made in my post, not trying to influence the OP, one way or the other, that is why I recommended the OP ask those who have had "eyes" on site to explain their sizing logic and the Pros and Cons of each, including a two stage gas valve and down-firing. Just trying to be as helpful as possible as i'm sure you are too.

ChrisJ

Fred said:

@ChrisJ
I don't want to take this thread off topic for this OP. My interest in understanding the OP's environment is more to understand how "Loose" or "tight" his envelope is and if that might affect how often the boiler might cycle, which certainly may affect the Pick-up/Piping load, at least in my opinion.
I stand by the suggestions I made in my post, not trying to influence the OP, one way or the other, that is why I recommended the OP ask those who have had "eyes" on site to explain their sizing logic and the Pros and Cons of each, including a two stage gas valve and down-firing. Just trying to be as helpful as possible as i'm sure you are too.

No.

JSR

Thanks to all for the responses!

In response to Fred: I have three steam mains: 17', 51' and 60', for a total of 128'. All are 2" mains. All are in conditioned space (i.e. the basement). Mains are insulated with asbestos, except for a few relatively short spaces, which I plan to insulate with 1" fiberglass. The house is brick and dates from the 1920's. It has insulation in the attic, none in the walls and it still has the original windows, which have old drafty storms on them. There is a fair amount of air infiltration around the windows.

New England SteamWorks

Fred said:

1) resolve the differences between your EDR numbers and those of the Installers so that you know what you really have.

That would be number one. We have to confirm the 506 EDR.

If it is indeed 506, then IN6 and make sure all the piping (including the near boiler, -which you will want in the bid) is insulated.

The IN7 will likely build pressure too quickly & short cycle. The IN6 should purr very quietly and efficiently (with correct near boiler piping) and heat just fine and with minimal pressure.

Another way to look at it: The radiators heat the house, not the boiler. Some Dead Man long ago did the heat lose calc on your home and sized the radiators. Very unlikely that he under sized them. If he did, not even an IN50 would help. So going bigger serves no purpose.

Contractors always oversize because there is no downside. Who would know? But if he undersizes and your home doesn't heat: catastrophe. Everyone knows and he eats it. Ergo: Over Size!

ChrisJ

RI_SteamWorks said:

Fred said:

1) resolve the differences between your EDR numbers and those of the Installers so that you know what you really have.

That would be number one. We have to confirm the 506 EDR.

If it is indeed 506, then IN6 and make sure all the piping (including the near boiler, -which you will want in the bid) is insulated.

The IN7 will likely build pressure too quickly & short cycle. The IN6 should purr very quietly and efficiently (with correct near boiler piping) and heat just fine and with minimal pressure.

Another way to look at it: The radiators heat the house, not the boiler. Some Dead Man long ago did the heat lose calc on your home and sized the radiators. Very unlikely that he under sized them. If he did, not even an IN50 would help. So going bigger serves no purpose.

Contractors always oversize because there is no downside. Who would know? But if he undersizes and your home doesn't heat: catastrophe. Everyone knows and he eats it. Ergo: Over Size!

Exactly!
And it doesn't matter how much steam you try to cram in them, it's not changing. As soon as you're making more heat than your condensers (radiators) can dissipate, you're losing the battle.

In a perfect world, the radiators should be able to condense more than the boiler can make, but that's likely risky for most installs.

SWEI

Hatterasguy said:

the heatloss of the building and the type of insulation used and the windows are all irrelevant in choosing a steam boiler.

Change that to almost irrelevant and I'll concur. When you start chopping piping and pickup factors off the standard math, the heat loss starts to become at least somewhat relevant.

ChrisJ

@JSR

Even more important, make sure the guy you hire, or, intend to hire tells you in detail of how this boiler will be piped.

As you've seen many of us already say, the piping is extremely important. More important than the boiler size.

You may think you're being a pain, or annoying him, but this is important. Once it gets piped wrong, it's a nightmare to try and get it fixed.

If you're unsure, post what he proposes here (NO PRICES PLEASE).

An IN6 + proper piping will be fantastic in your home, I'm sure.

New England SteamWorks

True: The heat loss is relevant to an extent: The radiators were sized to the original heatloss of the building. Assuming it hasn't been radically modified and chopped up into apartments or otherwise altered, if the building undergoes extensive weatherization and the heatloss is radically reduced, then the radiators will be over-sized. Which means the boiler could be smaller.

How much smaller is the question.

I like slightly smaller boilers. They run better 95% of the time. Worst case scenario: Every few years when record cold arrives, it usually only does so for a day or two, and so the thermostat slips a few degrees. To me, -worth it for the performance the rest of the year. I just make sure the owner buys in and understands the trade off.

Fizz

I was always under the impression that the stated rating of the boiler includes the pick-up factor, which would in this instance call for the IN7 or the New Yorker which is closer match.

SWEI

Fizz said:

I was always under the impression that the stated rating of the boiler includes the pick-up factor

Yes, and also the piping factor. That's where the system specifics start to factor in.

BobC

The rating of the boiler does not include the 33% pickup factor that is allowed for. A 500 sq ft boiler will supply 500 EDR and has a reserve off 33% (166 sq ft) for piping. That could be twice the pickup you actually need or even more.

Bob

KC_Jones

166 sq ft would roughly translate to 267 ft of 2" pipe, un-insulated. 2 3/8" OD X Pi=7.46" circumference X 12" =89.5 Sq in. divide by 144 to get sq ft = .622 sq ft of surface per foot of pipe. divide sq ft by .622 gives you pipe length for 2" pipe.

SWEI

The boiler's I=B=R rating in square feet includes both pickup and piping factors, which together come to 33% more than the Gross (DOE) Output.

JSR

Thanks to everyone for all their comments. What I am getting from all the discussion is that the the "Steam Sq. Ft." rating of the boiler does include a pickup/piping factor of 33%, which was my understanding from reading Dan's books. So, for example, the IN7 rating of 542 sq. ft. steam means it will supply heat to that much radiation plus heat all of the connected pipes and carry the load on startup. In other words, if the EDR of my connected radiation was 540 sq. ft., it would be a no brainer and I would probably pick the IN7.

I also take from all of the comments here that some of you feel the 33% pickup/piping factor is too large, especially if the pipes are well insulated and not in a crawl space or other uninsulated space. It sounds like many of you would apparently be comfortable using a pickup/piping factor of only around 15-18%. In other words, with respect to the IN6 rating of 450 sq. ft. steam, you would say that boiler is rated to heat 450 EDR and also to heat 148.5 EDR of piping (the 33% pickup/piping factor). Since well insulated pipes don't need that much, lets only set aside say 17% for the pipes and assume the other 16% (or 72 sq. ft.) will be available to the radiators. So adding 72 to 450 we get 522 and assume this boiler will heat 522 sq. ft. EDR.

Am I understanding this correctly?

Jeff

ChrisJ

JSR said:

Thanks to everyone for all their comments. What I am getting from all the discussion is that the the "Steam Sq. Ft." rating of the boiler does include a pickup/piping factor of 33%, which was my understanding from reading Dan's books. So, for example, the IN7 rating of 542 sq. ft. steam means it will supply heat to that much radiation plus heat all of the connected pipes and carry the load on startup. In other words, if the EDR of my connected radiation was 540 sq. ft., it would be a no brainer and I would probably pick the IN7.

I also take from all of the comments here that some of you feel the 33% pickup/piping factor is too large, especially if the pipes are well insulated and not in a crawl space or other uninsulated space. It sounds like many of you would apparently be comfortable using a pickup/piping factor of only around 15-18%. In other words, with respect to the IN6 rating of 450 sq. ft. steam, you would say that boiler is rated to heat 450 EDR and also to heat 148.5 EDR of piping (the 33% pickup/piping factor). Since well insulated pipes don't need that much, lets only set aside say 17% for the pipes and assume the other 16% (or 72 sq. ft.) will be available to the radiators. So adding 72 to 450 we get 522 and assume this boiler will heat 522 sq. ft. EDR.

Am I understanding this correctly?

Jeff

For the most part yes, I think you understand.

I currently have a 10% "pickup factor" and half of my piping is in cold drafty crawlspaces.

I've insulated most of the piping with 1" fiberglass pipe insulation, but got lazy and never went back and did all of the fittings. The system does just fine.

When it comes to boilers, and heating in general, slow and steady wins the race every time. The IN7 will work poorly. The IN6 will work awesome.

JSR

Thanks Chris. I am getting more comfortable with the contractor's recommendation and plan to discuss it in detail with him.

Let me ask one more question, would your recommendation change if I were to add 15-20 sq. ft. EDR to a sunroom in the next year or so to bring my total EDR up to a max of 526? I will discuss this with the contractor, too.

ChrisJ

JSR said:

Thanks Chris. I am getting more comfortable with the contractor's recommendation and plan to discuss it in detail with him.

Let me ask one more question, would your recommendation change if I were to add 15-20 sq. ft. EDR to a sunroom in the next year or so to bring my total EDR up to a max of 526? I will discuss this with the contractor, too.

My recommendation?
Probably not, just insulate the piping better and if need be slow venting down on the radiators. It'll still work fine.

I have an EG-40 rated for 325sqft connected to 396sqft of radiation. Half of my piping is in cold crawlspaces that often get near freezing temperatures. It just took extra tweaking of vents to get everything to work right and be balanced, but the end result is worth it.
Silence, always. Even during a long 9 degree recovery.



https://youtu.be/hH36luC9GKU




With added radiation, it may be a little more difficult to get things to work perfectly as far as balancing goes, but it is very doable as long as you put the time into it and overall performance will be far better than an IN7 ever will.

An IN7 is almost guaranteed to end up cycling on pressure with hissing vents. This will cost you money in fuel, as well as in vents over time.

That's my opinion based on the info you have supplied.

JSR

@ChrisJ. "Recommendation" was a poor choice of words. I understand it is only your opinion based on the available information. I do appreciate and value it though!

My system is a two pipe steam system so I don't have vents on the radiators to slow them down. Do I slow them down with the steam traps or with the main vents on the ends of the returns?

ChrisJ

JSR said:

@ChrisJ. "Recommendation" was a poor choice of words. I understand it is only your opinion based on the available information. I do appreciate and value it though!

My system is a two pipe steam system so I don't have vents on the radiators to slow them down. Do I slow them down with the steam traps or with the main vents on the ends of the returns?

I know very little about two pipe systems.
My guess, would be using the main vents, but I really don't know. Two pipe systems do offer a lot more control though, so I'm sure there is a way.

@Hatterasguy ??

ChrisJ

Hatterasguy said:

The simplest way to slow the steam on two pipe is via the use of orifices on the supply side. If the steam cannot easily get into the rad, it can't condense.

Wish we could do that on one pipe and dispense with these expensive PITA vents.

Where do you get orifices?

JSR

With respect to slowing down the radiators on the two pipe, I have three return mains on my system. One of them is connected to only the three steam mains. The other two drain the condensate from the radiators. It seems to me if I put a large main vent or vents on the return connected to the steam mains, that would get the steam to the risers and radiators quickly. If I put smaller main vents on the other two returns, it seems to me that would slow down how quickly the steam could enter the radiators. Does that make any sense?

Fred

I'd like to see @Steamhead or @Jamie Hall chime in on this venting issue. Venting on a two pipe system is, many times driven by the type of system you actually have and these two guys can best answer your questions. I'm sure they will ask a few questions and maybe want some pictures of any traps, etc.

Charlie from wmass

@JSR it would not slow it to each radiator as you want, just to all of them in varying degrees that I would wager do not equal comfort for you.inlet orfices tailor the steam.entering each radiator to meet your prefered demand. STATE Supply can get you the orfices. They need to know what your desired edr is for each radiator and you steam pressure. And the inlet size I believe.

ChrisJ

There are also two pipe TRVs I believe.
A TRV won't let a radiator get steam unless the room is cool enough. It basically creates a zone for each radiator you put one on.

Just another way to tailor the system to your liking.

JUGHNE

I have done orifices on a 2 pipe vapor system and removed the trap guts completely. They are placed into the inlet valve union. 80% or less of the rad heats and is enough heat for the house as many were designd to heat the house with most of the windows open.

Fizz

Another place to get orifices is Tunsten. You might want to check orifice chart that matches pressure to edr so that correct drill sized hole is done.

Charlie from wmass

Di you mean Tunstall ?

Fizz

Yes I did! Thanks Charlie.

vaporvac

Does your system use traps? Please don't mess with your venting before understanding what type of system you have. Could you post some pics of representative rads and the piping around your boiler? Your current valves may already be a metered type; adjusting them will control the amount of steam entering the rads. tw, these valves are still available from Mepco (I believe)?

PMJ

During an initial warmup or preheat when the entire system is at room temperature getting air out is not the issue, warming up the pipes is. So in a full preheat period an oversized boiler(high pickup factor) comes in very handy and cuts down the time required to get the mains warm a lot. But during outside conditions when you actually need heat a full preheat rarely is required. And once the insulated mains are warmed up, you simply can't run an oversized boiler with the tstat and pressure being the only burner control. Once a call for heat comes if the control system tries to run a big boiler flat out until the tstat is satisfied you will be cycling on pressure and overfilling rads. You will be overshooting and inefficient. However, simply spreading the total required burn time into smaller even pieces will work quite nicely - even with an oversized boiler. I like having the extra capacity there and don't think it is less efficient. Think short evenly spaced burns with vacuum coaxing the steam along to where it is needed between burns. I don't slow steam down at the rads - I just control the total volume of steam that can be produced per hour and spread its production out evenly over that hour.

I have also found that on a two pipe system the best venting improvement you can make is simply not to let the air back in after you push it out the first time. I think there are ways to pipe the vents on a one pipe system to accomplish the same thing. Hard to install for sure on an existing system, but the result would be even better than two pipe control.

jumper

It's likely that radiation was over sized in the first place so I'd choose the smaller output boiler. Thermostat control works better than pressure limit.

Fizz

Agree with PMJ. Have 478 SF of radiation, with a WM SGO 6,which has a steam heat rating of 654 SF. I switched to gas and had contractor fire the Wayne conversion at 186K. My pressure runs 1-2 oz. Two mos ago put system in vacuum and the numbers run 4-9Hg. Also changed CPH from 1(steam setting) to 3CPH(hot water) and ther results are as PMJ states. Heat is much more comfortable and without significant swings. No issues related to oversized boiler.

ChrisJ

Everyone claims the longer the run time, the more efficient the boiler.

I've yet to have anyone explain why this is, or isn't true but until that happens I'm going to follow that rule.

I like having my system run for 40-120 minutes doing a long recovery and yet still not building any significant pressure. I have to assume during those run times it's the most efficient.

Also, most people don't have access to a system like PMJ is running that can time it.

SWEI

ChrisJ said:

Everyone claims the longer the run time, the more efficient the boiler.

I've yet to have anyone explain why this is, or isn't true

When the boiler shuts off, heat goes up the flue. On natural draft appliances this happens mostly due to natural convection (note the increasing popularity of motorized flue dampers over the past couple of decades.) On forced- or induced-draft appliances, the post-purge circuit accomplishes a smaller version of the same effect.