Another discussion about steam boiler sizing

KC_Jones

Since several of us like to tinker with our systems and, to put it bluntly, buck the status quo, I wanted to do some testing on how important the pick up factor is in a steam system.

We have everyone from boiler manufacturers to contractors, basically the entire industry saying we must have an extra 33% or "bad things will happen". Well, I just don't buy it. There has been no hard evidence to prove this other than "That's the way it's always been done". Well, I hate that phrase, always have always will.

Now a few things about my system. According to the Slant Fin app I am not over radiated by a tremendous amount. My heatloss is ~60k and I have 270 EDR in the house which should provide 64,800 output at most, so radiation is not crazy oversized. This is uncommon, so I felt it was worth noting and an excellent test bed for my idea.

To that end, my boiler is currently firing at 3% BELOW the EDR of my system. Yes, I'm basically running at a negative pickup factor. I am firing at a gross input of 75k, and if we use the boilers rated efficiency gives me 61,500 gross output. In addition I also suspended the operation of the ecosteam control system. I wanted to see what a, in my opinion, properly sized boiler would do with no fancy controls. I have my Honeywell thermostat set to 2 CPH and all the intelligent recovery learning "stuff" turned off.

I've been running like this for a couple weeks and this morning was the first real test in my opinion. The morning outdoor temp was 8°F, my areas design temp is 7. My boiler had zero issues recovering from the nighttime setback, going from 70-72. It took some time, but it managed the recovery. I feel this also shows the amount of fudge factor that must be in the heat loss calculations. With the radiation I have and the heat loss I supposedly have, it should have been impossible, or close to, but it was a non-issue.

So, how has the performance been besides this mornings recovery? Well, in a word, fantastic. I get nice long run times, the system is silent, and I do mean absolutely silent. Prior to this it was very quiet, but I'd hear a random creak or slight hiss of a vent here and there. Now, nothing, absolutely dead silent. Since I'm heating much slower the radiators are staying hot longer. They heat so slowly to satisfy the thermostat I have a smaller portion of each rad hot for a longer period of time. This makes things very comfortable. On recovery I still have the rest of the radiator to heat up and make the recovery, again very slowly. At first the thermostat would overshoot, but I realized (with help from a friend) that the thermostat was relearning the heating rate as it's been running under the ecosteam for years. So at this point those issues seem to have been eliminated, the thermostat still isn't my favorite control, but with the lower firing rate I'd call it damn good, knowing the "smaller" boiler is what makes it great.

In addition I have not changed any venting in the house. I am still running the same main vents I've had for 10 years, still running the same radiator vents since I finished balancing about 9 years ago. Zero changes to that and zero changes to the balance in the house, everything is purring along just like it is supposed to.

My conclusion, I don't need any pickup factor. Boilers should be installed such that the pressuretrol is the safety it's intended to be, and honestly, based on what I'm seeing, with a properly sized boiler (by my standards) it would actually be impossible to build pressure...ever.

I fully appreciate the contractors aren't going to do this, I actually expect them to speak out against me. That's fine, it's not my business to run, it's theirs. What I am hoping is a conversation starts and we have some real talk about why the steam system "needs" all the extra. I want to emphasize the word need there, as need means the system will not function without it, which I feel is incorrect.

This is the ultimate iteration of keeping pressure low. For me, that is the ultimate in efficiency. This mornings recovery ran for ~2 hours continuously and my 15 ounce gauge wasn't even bouncing. Just quiet steam warming the house beautifully.


This forum was created by a man who saw things happening, applied some basic logic and said "we can do better". I'd like to think this website being established under that concept would make people open to more new thoughts and ideas on old systems, and that's what I'm presenting here, a new concept about boiler sizing.

Jamie Hall

I think you have a point -- but I would warn that every system is different. The system Cedric powers has a total EDR of 1500 (and, on cold days with wind, needs every square foot of it). Cedric himself is a Weil-McClain 580, but slightly down fired to 387,000 BTUh net. This gives a "pickup factor" of about 10% He does -- eventually (like about 45 minutes) reach his 6 ounce cutout pressure.

Honestly if I were a contractor or an engineer that's as close as I'd like to see it. There is enough potential error in calculating the actual total EDR of a system, and there's some play in the actual firing rate as well (I read somewhere -- can't remember where -- that the actual nozzle firing rate may vary by that much from nozzle to nozzle).

There is no harm, however, to selecting a boiler which has a minimum down fire specification of no more hand the exact EDR, and a maximum rate of no less than the standard pickup factor, and then -- if you have a friendly tech. or the instruments and skill to do it yourself -- to adjust the firing rate of the boiler to match the system more exactly (which is what we did -- close enough, anyway).

Mark N

@KC_Jones your signature shows you have a EG-40 boiler. According to Weil-McClain specs for the EG-40 the input is 125k and you state an input of 75k. Has your boiler been downfired and how does this effect efficiency?

ChrisJ

Mark N said:

@KC_Jones your signature shows you have a EG-40 boiler. According to Weil-McClain specs for the EG-40 the input is 125k and you state an input of 75k. Has your boiler been downfired and how does this effect efficiency?

If it did effect efficiency, it's likely in a negative manner and would produce less output if anything, therefore his test results are still valid.

ChrisJ

Jamie Hall said:

I think you have a point -- but I would warn that every system is different. The system Cedric powers has a total EDR of 1500 (and, on cold days with wind, needs every square foot of it). Cedric himself is a Weil-McClain 580, but slightly down fired to 387,000 BTUh net. This gives a "pickup factor" of about 10% He does -- eventually (like about 45 minutes) reach his 6 ounce cutout pressure.

Honestly if I were a contractor or an engineer that's as close as I'd like to see it. There is enough potential error in calculating the actual total EDR of a system, and there's some play in the actual firing rate as well (I read somewhere -- can't remember where -- that the actual nozzle firing rate may vary by that much from nozzle to nozzle).

There is no harm, however, to selecting a boiler which has a minimum down fire specification of no more hand the exact EDR, and a maximum rate of no less than the standard pickup factor, and then -- if you have a friendly tech. or the instruments and skill to do it yourself -- to adjust the firing rate of the boiler to match the system more exactly (which is what we did -- close enough, anyway).

Then we shouldn't be automatically applying 33% to all of them, since they're all different.

KC's results as well as mine are on single pipe residential systems and I'm starting to think they aren't that different. I have no idea about two pipe and larger systems and I try to avoid such discussions as I have no experience with it.

Steam systems aren't going to last forever.
But the more we can improve their performance the longer they will be around. Dan and others have worked hard pushing for guys to stop just replacing what's there and actually do an EDR survey, replace main vents etc. This has helped a lot of people who used to think whistling steam vents and banging were normal.

Maybe we can go even further than that. Maybe we can make silent single pipe systems that can absolutely can do a 5 to 10 degree recovery more common? Maybe we can get it so it's easy to setup residential systems to work well with something like the Nest and do setbacks and recoveries without overshoot and without headaches.

That would certainly make the average Joe more willing to live with steam.
And the only way we're going to actually know for sure is to try and keep trying.

Mark N

@KC_Jones your post reminded me of this article by @The Steam Whisperer (Formerly Boilerpro)

https://www.heatinghelp.com/systems-help-center/taking-another-look-at-steam-boiler-sizing-methods/

ChrisJ

Mark N said:

@KC_Jones your post reminded me of this article by @The Steam Whisperer (Formerly Boilerpro)

https://www.heatinghelp.com/systems-help-center/taking-another-look-at-steam-boiler-sizing-methods/

That's actually the article that made me want to start experimenting with my system.

KC_Jones

Mark N said:

@KC_Jones your post reminded me of this article by @The Steam Whisperer (Formerly Boilerpro)

https://www.heatinghelp.com/systems-help-center/taking-another-look-at-steam-boiler-sizing-methods/

That one has inspired my thought process as well, I'm definitely not the originator of these ideas, just bringing them back to the table.

ethicalpaul

This gives a "pickup factor" of about 10% He does -- eventually (like about 45 minutes) reach his 6 ounce cutout pressure.

@Jamie Hall does this pressure build even on the cold windy days you mentioned? Or on those days will it run all day without hitting cutout?

dabrakeman

I'll admit I never really fully understood design temperature. For my area it is also 7F but we can certainly get way colder than that. Some houses such as mine also have sections of steam pipe that pass through isolated areas of the basement that do not get ambient heating from the rest of the basement.

Kjmass1

What boiler do you have? I'm going through the same process, as I'm in need of a new boiler. I'm probably 3x oversized as is, and am thinking of downsizing some radiation to their actual heatloss prior to replacing the boiler. I'm around 300EDR right now. Is there a sweet spot for EDR once the boilers are on the small end? Or just size radiation to the heatloss, and let the vapor stat do the work?

Intplm.

Gee, I don't know?
EDR? Well always have done it this way with steam. And a proper heat loss calculation when sizing for hot water.
I do not want to tinker with these proven methods.
They have never let me down.

Jamie Hall

ethicalpaul said:

This gives a "pickup factor" of about 10% He does -- eventually (like about 45 minutes) reach his 6 ounce cutout pressure.

@Jamie Hall does this pressure build even on the cold windy days you mentioned? Or on those days will it run all day without hitting cutout?

He'll run 45 minutes to an hour, and then hits the cutout. Shuts off, post purge, by which time the pressure has dropped enough to reset the vapourstat, pre purge and then off we go for a while. Maybe half an hour to an hour if things are really tough outside. Rinse and repeat. At more normal (ho ho ho) temperatures -- say in the low single digits with no wind -- he'll run about the same coming out of a 2 degree setback (which isn't there to save fuel -- it's actually there to make our bathrooms nice and toasty when we get up) but the total run is never more than an hour, so he resets just the once.

ethicalpaul

Thanks! So I would say that you are in fact oversized, and you don't actually require every square foot, no?

ChrisJ

dabrakeman said:

I'll admit I never really fully understood design temperature. For my area it is also 7F but we can certainly get way colder than that. Some houses such as mine also have sections of steam pipe that pass through isolated areas of the basement that do not get ambient heating from the rest of the basement.

Because it doesn't stay below it for long, so those short periods are ignored. These are basically average numbers used with a rough calculation, nothing needs to be exact.

Worse case, the building temperature drops slightly during extremes but it allows you to size equipment closer to correct for "most of the time".

I think it's 5 degrees in my area but I've seen -8F and the record low is -19F I think.
My EDR is sized for -39F for what it's worth which means my boiler with a 10% pickup factor can easily heat my house down to 44 degrees below design temperature.

I've got a boiler rated for 325sqft connected to 392sqft.

dko

Wow you guys have been around a long time!

https://forum.heatinghelp.com/discussion/149940/pickup-factor-help-me-understand

It's so interesting to read posts from the same people 10 years ago

ChrisJ

dko said:

Wow you guys have been around a long time!

https://forum.heatinghelp.com/discussion/149940/pickup-factor-help-me-understand

It's so interesting to read posts from the same people 10 years ago

Never stop learning.

@gerry gill 's link was one of my favorites and I learned a lot from it. : https://www.ideals.illinois.edu/handle/2142/4349

Jamie Hall

ethicalpaul said:

Thanks! So I would say that you are in fact oversized, and you don't actually require every square foot, no?

It's worth remembering that there is another factor involved here. How warm do you want to keep your structure -- or how warm can you afford to keep your structure. In Cedric's case, for instance, he is designed to maitian the house at 72 F, and the original specifications called for going down to -15 F (no design day temperatures in those far off days!). That's a delta T of 87 F, and there was an allowance for wind added in to that. In fact, for economy, the house is actually kept at 61 F. If we tried to keep it at 72, we cold do it -- but at 3.3 gallons per hour, we are not going to do that, as then Cedric would run continuously.

From the designer's point of view, it is prudent to have a margin of performance beyond what is actuall required. Very few people will complain if there is a bit left when conditions are as tough as they are ever going to be -- but very few people WON'T complain if they can't get to where they want to be, or something breaks...

KC_Jones

dko said:

Wow you guys have been around a long time!

https://forum.heatinghelp.com/discussion/149940/pickup-factor-help-me-understand

It's so interesting to read posts from the same people 10 years ago

That is a throwback. I forgot about that thread actually.

ChrisJ

Jamie Hall said:

ethicalpaul said:

Thanks! So I would say that you are in fact oversized, and you don't actually require every square foot, no?

It's worth remembering that there is another factor involved here. How warm do you want to keep your structure -- or how warm can you afford to keep your structure. In Cedric's case, for instance, he is designed to maitian the house at 72 F, and the original specifications called for going down to -15 F (no design day temperatures in those far off days!). That's a delta T of 87 F, and there was an allowance for wind added in to that. In fact, for economy, the house is actually kept at 61 F. If we tried to keep it at 72, we cold do it -- but at 3.3 gallons per hour, we are not going to do that, as then Cedric would run continuously.

From the designer's point of view, it is prudent to have a margin of performance beyond what is actuall required. Very few people will complain if there is a bit left when conditions are as tough as they are ever going to be -- but very few people WON'T complain if they can't get to where they want to be, or something breaks...

But design day temps + heatloss calculations include all of that no?

EBEBRATT-Ed

There are so many variables involved.

But steam will be around for a while. I have always felt that a 33% pick up was too much for a house. Even at 1 cph the piping never really gets cold. And at temps above design you have extra capacity and as you reach design temp the boiler is running often enough so that pick up is a moot point.

But there are a lot of commercial and industrial boilers that do more than heat a building. A factory may run the boiler hard in the morning and need the pick up load figured in, During the day machines are running , lights are on and the building is full of workers and the building won't need as much heat.

Bottom line is every job is different.

Blanket statements don't work everywhere.

But as far as the average house if the piping, venting and radiation is correct and the boiler is sized right little if any pick up is needed.

ChrisJ

EBEBRATT-Ed said:

There are so many variables involved.

But steam will be around for a while. I have always felt that a 33% pick up was too much for a house. Even at 1 cph the piping never really gets cold. And at temps above design you have extra capacity and as you reach design temp the boiler is running often enough so that pick up is a moot point.

But there are a lot of commercial and industrial boilers that do more than heat a building. A factory may run the boiler hard in the morning and need the pick up load figured in, During the day machines are running , lights are on and the building is full of workers and the building won't need as much heat.

Bottom line is every job is different.

Blanket statements don't work everywhere.

But as far as the average house if the piping, venting and radiation is correct and the boiler is sized right little if any pick up is needed.

True.
But even commercial forced air is treated totally different than residential no?

Kjmass1

EBEBRATT-Ed said:

There are so many variables involved.

But as far as the average house if the piping, venting and radiation is correct and the boiler is sized right little if any pick up is needed.

Isn't it a problem if the radiation hasn't been changed? If you size to radiation, and the home has been insulated, air sealed and has new windows since the last time the boiler was installed, you are sizing to huge loads. I have some 12k btu/hr radiators, 4 of those would satisfy my entire house at 9 degrees. So you either need to pull some out or make them smaller, or else you are putting in a boiler much too big.

Mark N

@Kjmass1 no need to replace or remove radiators. The vast majority of the winter my rads never heat more than 1/2 way. If it's really cold maybe 2/3 of the way. The thermostat has been satisfied and the boiler has turned off. Also, my boiler was sized the conventional way using a 33% pickup. I have a hot water zone off of my boiler, so the pickup is needed for my situation.

ChrisJ

Mark N said:

@Kjmass1 no need to replace or remove radiators. The vast majority of the winter my rads never heat more than 1/2 way. If it's really cold maybe 2/3 of the way. The thermostat has been satisfied and the boiler has turned off. Also, my boiler was sized the conventional way using a 33% pickup. I have a hot water zone off of my boiler, so the pickup is needed for my situation.

Are you sure?

Mark N

I'd hate to find out that possibly the boiler couldn't make steam when the hot water zone kicked on.

ethicalpaul

Mark N said:

I'd hate to find out that possibly the boiler couldn't make steam when the hot water zone kicked on.

That would never happen. The hot water zone is (should be) only pulling 180 degree water out (due to the mixing that your piping should be doing--what I mean is the quantity of 212 degree water coming out of the boiler into the loop is lower than what the loop is circulating) and the BTU load of your loop is very small compared to what's going into the boiler.

Mark N

@ethicalpaul I'm going by what I've read. This is from "We Got Steam Heat"

"Finally, I have to tell you about a few limitations with these hybrid systems. First, there's only so much heat you can take from your boiler before you won't be able to make steam. You can safely use a third of the total output of the boiler (its Gross rating)."

Kjmass1

Mark N said:

@Kjmass1 no need to replace or remove radiators. The vast majority of the winter my rads never heat more than 1/2 way. If it's really cold maybe 2/3 of the way. The thermostat has been satisfied and the boiler has turned off. Also, my boiler was sized the conventional way using a 33% pickup. I have a hot water zone off of my boiler, so the pickup is needed for my situation.

Sure it works, but is it the most efficient way of running a boiler? Guess I'm asking is there much of a difference of say a 80k boiler that runs a full hour at design day, vs a 160k boiler that runs 50% of the hour at the same temperature?

ethicalpaul

Mark N said:

@ethicalpaul I'm going by what I've read. This is from "We Got Steam Heat"

"Finally, I have to tell you about a few limitations with these hybrid systems. First, there's only so much heat you can take from your boiler before you won't be able to make steam. You can safely use a third of the total output of the boiler (its Gross rating)."

Tell me what percent of your boiler's output your loop is using. But also that paragraph is wrong. You will still make steam if you should (you won't) use more than 1/3 of the boiler's output...it just might be less steam than your whole system needs. But that would be one monster of a hot water loop.

Mark N

@ethicalpaul when the hot water loop was installed, I used the advice on how to properly install a hot water zone off of my steam boiler as provided by @DanHolohan and Noel Murdough. I've never had any issues with it over the last 14 years.

ethicalpaul

Congratulations!

EBEBRATT-Ed

The idea behind the hot water loop not being more than the pickup capacity of the boiler is that if the boiler is perfectly sized for the steam radiation and you are at design conditions the boiler may not generate enough steam with the hot water loop calling.

In the real world the hw zone won't be on all the time anyhow

Intplm.

Intplm. said:

Gee, I don't know?
EDR? Well always have done it this way with steam. And a proper heat loss calculation when sizing for hot water.
I do not want to tinker with these proven methods.
They have never let me down.

I haven't had an installation problem since I have become a student of Dans books. Not one that has had a customer uncomfortable.

While I read into this post, Im trying to relate to its purpose/learn something helpful.

dko

There is working, working well, and working great.
There is good enough for the customer, good enough for me, and good enough for heatinghelp.
Correct way, better way, best way.
All depends on your standards.

KC_Jones

Intplm. said:

Intplm. said:

Gee, I don't know?
EDR? Well always have done it this way with steam. And a proper heat loss calculation when sizing for hot water.
I do not want to tinker with these proven methods.
They have never let me down.

I haven't had an installation problem since I have become a student of Dans books. Not one that has had a customer uncomfortable.

While I read into this post, Im trying to relate to its purpose/learn something helpful.

So the only criteria is callbacks? If that's so there is no point in sizing any equipment properly. You could throw any oversized thing on almost any system and not get callbacks.

We are currently exploring if that 33% makes sense. Just because something has been done for years, doesn't mean it's the only way, and honestly, doesn't mean it correct either. We should always be learning and experimenting...always.

ethicalpaul

Intplm. said:

I haven't had an installation problem since I have become a student of Dans books. Not one that has had a customer uncomfortable.

While I read into this post, Im trying to relate to its purpose/learn something helpful.

I think this is great, but it's really not the point of this post. I think we all agree that even a greatly oversized boiler can successfully heat a house with no complaints. But there may be a lot of room between that and a much smaller boiler that works better.

Jamie Hall

It might be well to keep in mind that the original pickup factor -- I'd rather call it a safety factor -- was 50% Quite some time ago it was reduced to 33%, and that figure is baked into the EDR rating (but not the net steam output BTUh) of the boiler; I believe it is part of the ASME standard.

Which doesn't mean that it's a code requirement. It isn't. The code requirement, in almost all building codes, is that the equipment provided shall be able to maintain a certain minimum space temperature -- usually, I think, 72 F, at the design conditions, which today means the design degree day for the location.

How you, the installer, go about doing that is your business. Some code people will check your work, in which case you will need to justify what you have installed if it doesn't just tick the boxes, and some won't, in which case it's your pigeon -- until someone gets upset that their Aunt Martha is cold.

Should you use 33%? That's really a judgement call on your part. If yo are an installer, and the boiler which you are installing has the option to down fire, and the homeowner is willing to pay for your time to do the adjustment after installation, then I'd be likely to size the boiler to the 33% and expect to try down firing it later. If the homeowner isn't willing to pay for that, if it were me I'd use the 33%, fire it at 20% or so, and then if the homeowner has a problem expect to come back and adjust it -- one way or the other. If I were a homeowner, I'd expect the same from the installer -- but if I insisted on using a lower rating, I'd expect that it it didn't work out that I'd be left with the puppy, not the iinstaller.

If it's a commercial job, or one with an architect or engineer, put in what is on the plans. Then it's their problem if it doesn't work.

One other note, however. This not about efficiency. A boiler which short cycles some does not lose much in efficiency. A little, but not much. It's about perception.

ChrisJ

Jamie Hall said:

It might be well to keep in mind that the original pickup factor -- I'd rather call it a safety factor -- was 50% Quite some time ago it was reduced to 33%, and that figure is baked into the EDR rating (but not the net steam output BTUh) of the boiler; I believe it is part of the ASME standard. Which doesn't mean that it's a code requirement. It isn't. The code requirement, in almost all building codes, is that the equipment provided shall be able to maintain a certain minimum space temperature -- usually, I think, 72 F, at the design conditions, which today means the design degree day for the location. How you, the installer, go about doing that is your business. Some code people will check your work, in which case you will need to justify what you have installed if it doesn't just tick the boxes, and some won't, in which case it's your pigeon -- until someone gets upset that their Aunt Martha is cold. Should you use 33%? That's really a judgement call on your part. If yo are an installer, and the boiler which you are installing has the option to down fire, and the homeowner is willing to pay for your time to do the adjustment after installation, then I'd be likely to size the boiler to the 33% and expect to try down firing it later. If the homeowner isn't willing to pay for that, if it were me I'd use the 33%, fire it at 20% or so, and then if the homeowner has a problem expect to come back and adjust it -- one way or the other. If I were a homeowner, I'd expect the same from the installer -- but if I insisted on using a lower rating, I'd expect that it it didn't work out that I'd be left with the puppy, not the iinstaller. If it's a commercial job, or one with an architect or engineer, put in what is on the plans. Then it's their problem if it doesn't work. One other note, however. This not about efficiency. A boiler which short cycles some does not lose much in efficiency. A little, but not much. It's about perception.

It's far from a safety factor at least that's my interpretation.


Please read the link from earlier and tell me your thoughts on it.  Id appreciate them.

https://www.ideals.illinois.edu/handle/2142/4349

Jamie Hall

I'm a computer klutz. How do you open that?

As I noted, I prefer to think of it as more of a fudge factor, to account for the various inaccuracies in all of the measurements and specifications involved. A safety factor --to my engineering and pilot's mind -- is there to ensure that there is a genuine margin between the rated working load and the point where things start to get bad -- whether from variations in material or from wear and tear, or just ordinary wild deviations. In my work I've used safety factors ranging from 1.2 or so right on up to 8 (overhead cranes and rigging). People who don't are either putting their personal fortunes, if any, or their lives on line... not like HVAC work1

ChrisJ

Jamie Hall said:

I'm a computer klutz. How do you open that? As I noted, I prefer to think of it as more of a fudge factor, to account for the various inaccuracies in all of the measurements and specifications involved. A safety factor --to my engineering and pilot's mind -- is there to ensure that there is a genuine margin between the rated working load and the point where things start to get bad -- whether from variations in material or from wear and tear, or just ordinary wild deviations. In my work I've used safety factors ranging from 1.2 or so right on up to 8 (overhead cranes and rigging). People who don't are either putting their personal fortunes, if any, or their lives on line... not like HVAC work1

This isn't the same as those in my opinion.

That link should open a website where it lets you read the text in a viewer.  It also has a download button to download it in .txt format which you can open in notepad if you want