Better to Undersize or Oversize

saikosis

Hi. While I'm waiting for quotes to come in from the contractors, I'm wondering whether it's better to undersize or oversize a boiler when your EDR falls between two sizes.



Let's say I have 420 square feet of radiation. That puts me smack in the middle of the Peerless 63-04L and 63-04. For the sake of argument, assume those are my only two boiler options and that tricks like downfiring aren't possible. Also assume that the pipes are insulated, the house is mostly unchanged since the radiators were installed, and that there are no plans to add or remove radiators.



In this case, is it better to go with the 63-04L with 383 square feet or the 63-03 with 458 square feet?



I've read the article about boiler sizing (<a href="http://www.heatinghelp.com/article/323/Boilers/1551/Taking-Another-Look-at-Steam-Boiler-Sizing-Methods-by-Dave-Boilerpro-Bunnell">http://www.heatinghelp.com/article/323/Boilers/1551/Taking-Another-Look-at-Steam-Boiler-Sizing-Methods-by-Dave-Boilerpro-Bunnell</a>), but I'm not sure how to apply it.



My naive assumption would be that the larger boiler would be better on the coldest days while the smaller boiler would be better the rest of the time. Therefore, if you expect few "design days," slightly smaller is better than slightly bigger. Conversely, if you expect many design days, slightly bigger is better.



Is there a rule of thumb about how far off you can be from the rated capacity of the boiler? For example, if I had 384 square feet, the 63-04L with 383 would work, right? At what point does it flip and I'd be better off with the bigger 63-04?



I'd appreciate any input from the experts who know what happens in the real world. Thanks.

Bio

Sizing

If you have 384 sq/ft. The smaller is the perfect boiler for you, it will work fine on the coldest days of the year, remenber that most of the time radiators are oversized for the room they're in, in my case my radiators only heat up the top third and on the coldest day close to half of the radiators and that will satisfy the thermostat, vent your mais fast and radiators slow, I use Hoffman 40 on all radiators  

saikosis

Hypothetical

Just to be clear, the sizes I'm talking about here are hypothetical. I'm hoping to learn some of the theory behind sizing. I'm trying to get a sense for what's too small and what's too big.



I made up the numbers above, but it turns out that I can actually use my real numbers and end up with a similar example. I have 343 square feet. That puts me almost exactly between the Peerless 63-03 at 308 and the 63-04L at 383. Again, assume my pipes are insulated and my house is mostly unchanged. Should I go up the to 63-04L or down to the 63-03?

Joe V_2

undersize

Hypothetically, you should go with the smaller boiler because it has an automatic pick up factor of 33% built in.  If you are well insulated and have no plans to add radiation, you'll still be a measure larger than you need to be. 

saikosis

Summary

So is it safe to say:



1. Get the boiler that's as close as possible to your radiators.

2. If you're between two sizes, go smaller.

3. Insulate as much as possible.

Joe V_2

Yes

1.Yes.  You are very close to an exact match. 

2. Yes-especially if well insulated. But if you are not, that that extra 33% pick up factor may actually make the smaller boiler slightly larger than what you need for those exceptionally cold days.

3,. Yes 



I should add:  Disclosure-I am a homeowner



 

saikosis

Thanks

Thanks, Joe. I appreciate the second opinion.

ChrisJ

Undersize

I'm just a homeowner but I agree. Undersize the boiler, vent the mains fast and vent the radiators very slow. Of course insulate every bit of piping possible with 1" or thicker insulation.



The system will work beautiful.

bob young

boiler sizing

how could you possibly go wrong with a home owner sizing your boiler & giving you technical advice. i find that hilarious. **** is going on in this forum ???would i tell my doctor how to install a stent ?  nah.

Unknown

where is the???

Where is the "thank" button for Bob's comment??

ChrisJ

Really?

Bob, We very often find guys who know nothing about steam, or close to nothing installing boilers and making homeowners wish they had done differently.  It is ALWAYS best to do research here prior to having one installed and more often than not folks are happy that they have.



More often than not we see boilers piped wrong and grossly oversized.

Eastman

advice

 What advice is incorrect?

saikosis

So What's the Answer?

Bob, with all due respect, my question has been up here for three days now and the only responses came from homeowners. We all know that the pros are busy and that this site is free, so we're happy when we get any advice from them at all. I certainly don't get upset or annoyed if I don't get a response from a pro, but, that said, I do still need to get some answers so I can make informed decisions for my home. That's where the other homeowners come in. We're all just trying to do the best we can to learn about these systems and help from homeowners like ChrisJ and Joe V go a long way. Both are them were upfront that they're "just a homeowner," so I'm obviously going to be more cautious with their advice than with a pro's advice (no offense Joe and Chris). I think all of us would be really happy if a pro replied saying, "No, you're wrong because..." or whatever. We'd all learn something, I'd end up with a better system, and we could turn around and give better answers to the next homeowner who asks the same question, so everyone would win.



So all that said, what's the answer? Is it better to oversize or undersize? Why? Is there a rule of thumb or does it depend on each system? Let's get some answers from the pros so we can all be more informed.



Thanks everyone.

stevep

Sizing

I'm a homeowner as well. That said, I attended Dead Man's steam school and the first subject out of Dan's mouth was boiler sizing. The old steam systems were designed to heat the house on the coldest day of the year, with the windows wide open. It seems to be common practice to undersize boilers nowadays since we're now heating these same homes with the (double pane) windows closed, and insulated walls and attics.

Dave in QCA

OK, OK, I'll jump into the fray!

I have so far avoided commenting on this thread because I hoped that one or two of the pros would jump in. And... because everytime I looked at the original question, all I could think of were semi-inappropriate off-topic answers, such as, "Bigger is Always Better!" Or, "its not the size that counts, its how you use it." Ha ha ha!



Back to the subject of steam boilers! Which is better, undersize or oversize? The answer is neither. Both can cause problems. The best thing is to size the boiler accurately. Plus or minus 1 or 2% will not make a measurable difference. If you have a situation where your system is midway between two available boiler sizes, it is a scenario prone with issues. Since Dan recommends a higher piping and pickup factor of 50%, you can look at that and decide that you are still within those parameters and go larger. It will work fine, but on long firing cycles you will have short cycling of the boiler after pressure is established in the entire system.



On the other hand, if you use Dave Bunnell's approach and under size, you may have a slightly more efficient system and you will spend slightly less for a boiler. But, proper operation of this boiler will be very sensitive and will require very slow radiator vents. If you use radiator vents that are too fast it will make the system impossible to balance. I suppose that is why many installers oversize. No one wants callbacks because one or two radiators won't heat.



In a previous thread, you have indicated a reasonable plan for sizing your boiler and proceeding. I would do EXACTLY what you have indicated if it were my system. As for the question, "better to under size of oversize?" There is no simple answer, as neither is better.



As to Bob's comments, whether heart stints or steam boilers, being an informed consumer is never a bad thing. But, the comparison of the two is bogus in the first place. The heart surgeon is required a specific amount of education and training that qualifies him/her with the specific knowledge and training to do the job. Additionally they must past an additional rigorous examination process to become board certified in their specialty. The same does not exist for steam boiler contractors in most places. A plumbing or perhaps a mechanical exam is required to get a plumbing and heating license, but usually no testing about steam installation. From the installs that I have seen in person as well as the many that have been pictured here, it becomes apparent that many installers have no basic understanding of steam systems and often cant even read the installation manual. The homeowner, novice, and consumers that end up here do so out of necessity. In the best situations, it is simply education to be an informed consumer. In the worst cases it is self preservation against bumbling incompetent knuckleheads that think they know how to install a steam boiler.



Now if you went into the hospital for a heart stint and came home with stitches on your hemorrhoids, you'd have a clue that something went wrong. When people buy a steam boiler they expect that it will work properly and will last a long time. In all too many cases, the consumer gets neither and they often don't find out until several years after the bill was paid.



Bob, Maybe you would consider using your knowledge to help both consumers and contractors, as BOTH come to this forum looking for help and advice.

Dave in QCA

And Dan's next words were....

As a result, many times some of the radiators have been removed. In a hot water system you can size for building heat loss, but in a steam system, you have to size to the connected radiation.

ChrisJ

Yep

I'm a big fan of Dave Bunnell's approach but I can agree with Dave from personal experience that undersizing makes things very picky and my system isn't really undersized.



I work on two other steam systems besides my own, both of which are oversized and they behave absolutely nothing like my own. On my system if I vent a radiator too fast I loose heat in other rooms even if they are on a different steam main. Where, the other two oversized systems I help friends with would still heat every room even with every vent completely removed. Personally I prefer an undersized boiler but it does take time and a lot of fine tuning to get working right.



I also had a weird problem with Hoffman 1As getting plugged with water. A little drop of water would form in the valve orifice and cause the radiator to stop heating completely until I cleared it using a can of air and a straw. Have not had that problem since I switched to Gorton vents.



All of that said I personally, would still lean towards undersizing rather than oversizing if those were my only options.

Joe V_2

I'll jump in too

Residential steam heating  is dying.  Every year, I see homes gutted for remodelling with radiators stacked to the side of dumpsters waiting for their trip the the scrap metal yard.  Pros in residential steam heat are disappearing. In North Carolina, they dont exist.  That's why the  book is titled the Lost Art of Steam heat.  We love to hear from the pro's and appreciate their feed back. 

My project of restoring a residential, 1930 Trane vapor system wouldnt be possible without this site.  In fact, because we lack pro's down here, I had a furnace/central air system put in when my boiler original boiler cracked.  But my love for steam heat and  knowledge that is is the best available made me take on the project of restoring it.

I always try to add to the bottom of my posts a disclosure that I am a home owner so the OP can validate the value of my posts.  But on this one, I will add an additional disclosure:

Disclosure: I am a homeowner, but professionally, I am responsible for the safety,maintenance, efficient combustion and continuous improvement of:

Three 600HP Hurst Boilers, five 400HP Cleaver Brooks, Two 200HP Kewanees, and three C-B 3000 hot water boilers.

This site helped me save a piece of history.  I will use my experience from that project to pay it forward.

Y'all can start hitting the "Thank You" button any time now ;  )

JohnNY

Thank you, all, for your wonderful contributions.

bob young

Homeowners

John, for the most part the homeowners are pretty respectful when they get a little knowledge from us but  some get really brazen & start giving advice & other homeowners not knowing any better eat it up. sadly to say a lot of them are just cheapskates too frugal to hire a lic. master plumber or qualified heating professional . they are just trying to do a home job & fish for free information. just so happens they found this forum where some of the most astute heating experts in the world are not opposed to share a whole lot of expertise & trade secrets.then they do one job that works out well thanx to us & they become groupie experts. then and this is the best part they think they know more than us & start instructing us about our own profession. like i said...." **** just happened !!"   and yes i repeat, a little bit of knowledge is a dangerous thing. bob young  young plbg. inc. nyc lic. master plumber.

Unknown

hey Bob

Comn on Dan, where's another thank button for the last Bob's comment again??

Joe V_2

sorry

you feel trespassed on. but this is an educating site.

stevep

Sorry to continue the derail, but...

...after what I've been through trying to figure out my system I feel very fortunate to have found this forum. We bought our first home 8yrs ago and hired a highly recommended home inspector who passed the steam boiler with flying colors. I know now that the installation would have been in the top 10 of the shoddy boiler installation hall of fame. When we discovered the boiler had a cracked block a few years later, the oil company who serviced it wanted to replace it using the existing near boiler plumbing which was horribly wrong (and copper). We were lucky enough to stumble across a contractor who could get the job done quickly and knew a thing or two about steam. Only problem was he didn't properly skim and clean the boiler and was unreachable after the installation leaving me to wonder what the heck was wrong with it.



Bottom line is there are a lot of folks out there who are doing crappy work and you have to be an informed customer. It's nice to read some feedback from the pros who know the in's and out's of steam. I've checked out the photo albums of the pros on this forum and I marvel at them. Very impressive.



But, I've also found the questions and answers from other homeowners equally as helpful for a number of reasons.



Also, it's winter which is my down time. When it's not boating season I have to tinker with something or I go nuts. The steam boiler in our house fascinates me now that I have it running well. I know, I'm a nerd.

JStar

Sizing

The answer is pretty simple. Install a wet-based boiler with a power burner. Fire it at the EXACT rate that you need. Not under or oversized. Or even better, undersize the firing rate, and witness first hand how it runs in the winter.

DanHolohan

To those who are being not nice.

Please keep in mind that I, too, am just a homeowner. I have a drivers license and a marriage license but that's it. I don't turn wrenches. What I do is study and listen hard to what others have to say. I consider others' opinions and I have a lot of opinions of my own, mostly because I keep them to myself unless asked for one. I'm just a homeowner but lots of pros come to me for advice, as I go to others for advice.



I set few rules for this site but the first was to be nice. That seems like a good rule to me. I've been at this since '96 and have watched what happens when people get nasty with each other, and act crude by using expressions such as ****. I can't imagine a pro using that crude expression in a customer's house.



Be nice or be gone. That's a choice.



And please don't post your company name and location if you're not listed in Find a Contractor. It's not fair to your fellow professionals who pay for that option.



Thank you.

Dave in QCA

Perfect Answer

Joe comes up with the 100% most accurate answer. Don't know why I didn't think of it as I did install a wet base boiler and tuned the burner to the load. It works great!

BobC

We are all here to learn

i know people have different ideas on how a thing should be done and the great thing about this forum is that homeowners who care about steam get to interact with the pro's who do it every day. We all know the number of good steam men is dwindling fast, please bear with those of us who are trying to help someone climb the ladder towards better understanding of steam systems. If we say something that is wrong we should be told what is right so we can all increase our understanding.



After my engineering job succumbed to the economic imperative we call China i ended my working career as a technician working on mail sorting machines at the post office. These machines are large and complex, they send you out to school for anything from 2 to 12 weeks to learn the machines operation and maintenance. As the new guy I made my share of mistakes but my previous training allowed me to see things that others did not because of the way i had been trained. I studied and worked on the machines and was grateful to the mechanics and techs who showed me the ropes there, they gave me insight that can take years to gather.



There were some who would not share what they knew because "they had to learn it the hard way and you'll have to learn it the same way". i never operated that way in the army as an NCO and I never did it as a technician, engineer, and finally a manager at my old job. As i learned I passed whatever knowledge I had with others that were not familiar with the machines because they were new hires or because they had worked in different areas. When i had to retire because of some physical problems a couple of the younger guys thanked me for showing them how things worked and for letting them make mistakes without fearing ridicule for making an honest mistake. i still get together with members of the crew for lunch a few times a year (I retired in '09) and i respect them for the work they do every night.



A good teacher knows he will learn from those he teaches. We all see things differently and we can all learn from each other.



Bob

VA_Bear

And you are still teaching BobC...

A lesion made eloquently and succinctly, sir and a reminder to us all that we have a place to learn and a place to teach. To know requires only knowledge, however to teach requires understanding as well.