New steam boiler sizing question?

Rusty2

I've calculated the EDR from my radiators at 504 ft. square of steam. Mains are all insulated. I'd like to go with a Burnham MegaSteam, either MST396 or MST513. 3" Drop header with 36" off the water line is piped and waiting for a boiler. Someone advised me that I could get away with an MST396 because they typically subtract 15% of the EDR. I want dry steam to make it to the furthest radiator, but at the same time don't want to be constantly short cycling. What are your thoughts on this? Thanks

Steamhead

Use the 513. The 396 is way too small to work for you. You could always down-fire the 513 a bit if needed.

Rusty2

Thanks Steamhead.

PhilKulkarni

I have a similar question. My Sunrads are recessed and to calculate the resulting EDR from the freestanding EDR for each radiator from the specs, I derated the total by 10%. Is that a reasonable factor in sizing the new boiler?

With a drop head, is the ‘A’ dimension still measured from the center of the water gauge to the top of the elbow on the 2” takeoff or is it to the bottom of the equalizer pipe? That pipe would be the lowest steam carrying pipe as it comes down approx 5” from the top of the elbow.

Thank you in advance.

Steamhead

@PhilKulkarni , are your steam mains parallel-flow (sloping down from the boiler) or counter-flow (sloping up from the boiler)?

The Sunrad chart says for recessed units, add 5% to the calculated requirement if there is 3/4" air space at top and sides with 1/2" in back, and add 15% if not. Which is your situation?

PhilKulkarni

The header connects to the with a 45 to the main which slopes up from the boiler goes into a bull head tee and both sides of the mains from the tee slope up. They both then have a 90 degree elbow and slope down towards the wet returns. The risers are on these downward sloping sections where the steam and condensate travel in the same direction. I have attached pics.

In the attached image, the radiator which is 20” high and 63” wide and has 27 openings and 28 sections has a rating of 63 sq ft EDR while free standing. There is an 1/8” space at the top and sides, 1/2” at the bottom and slightly more than 1/2” clearance at the back. What is the estimated EDR?

Thanks in advance.

Steamhead

I worked the math backward- if totally recessed with no clearances the rating would be about 87% of the free-standing rating. For that one, it would be 54.8.

If all the radiator take-offs are on the part of the main that slopes down from the boiler, it's parallel-flow.

PhilKulkarni

Thanks @steamhead. That is close to the 90% I was going to use. With a total EDR of 270 using 90% derating for recessed rads in my house, I looked at boiler specs of various brands mentioned on this forum and I see a smaller mismatch of boiler EDR capacity on the higher side, which begs the question: Am I better off under sizing the boiler by say 5% or over sizing it by 5%? The cost difference between the two options is between 8-11% based on the prices I see on the internet. This differential may be different when priced by installers.

A near boiler question I have is if there is a minimum height for a drop header from the center of the glass gauge? Does its height impact steam saturation in any way? I have searched several threads on drop headers but they only mention riser heights.

Thanks in advance.

Jamie Hall

%% over or under is about as close as you're going to get and won't make much difference either way. If all the mains are well insulated, I'd go a little under on EDR.

As to the drop header -- well, it does need to be above the water line of the boiler -- it should be at least above the top of the sight gauge. But it doesn't need to be any higher than that. You're riser will go up as usual, and then come down to the drop header. Just make sure it's pitched to the equalizer.

PhilKulkarni

Thanks @Jamie Hall. My pipes have mostly 1/2” or better insulation including the returns.

I want to recognize your insight some months ago on a thread here about my boiler using a gallon of water a week without any apparent steam or water leaks. You had correctly diagnosed that the boiler was leaking and driving the steam up the chimney. The situation lasted for an entire heating season culminating in the boiler producing no pressure and a dead system by the end of April. I took a vacation to Florida to mitigate the attendant discomfort: not too shabby after being cooped up for two years during the lock down.

The Crown is ten years old and still under warranty. The installer in 2012 did not do a capacity calculation but merely replaced the old Burnham, circa 1978, with this one of comparable capacity. This boiler is rated at 357 sq ft of steam against the 270 I calculated, small wonder then it cycled on pressure approx every 3 mins on a warm cycle. As if this weren't bad enough, it also produced wet steam despite a dropped header on the single takeoff. This manifestly left all my nine radiators gurgling and venting air on new MOM vents. On those nights I craved for a restorative sleep, I simply unscrewed them, poured out the water and put them back on, and that quieted them, albeit temporarily. Trying to quiet them with smaller orifices did nothing when it was 10F outside. Six years ago, I installed a time delay relay and reduced the CPH to 4 on cold days but the boiler succumbed to the relentless cycling and died nevertheless. Hence my paranoia about EDR and boiler sizing, which I will hopefully divest after a new boiler is installed.

Thanks to everyone who assisted-much appreciated.

mattmia2

Short cycling won't kill a boiler. Keep looking.

Jamie Hall

mattmia2 said:

Short cycling won't kill a boiler. Keep looking.

But excessive water use will. How much water were you using?

PhilKulkarni

One gallon every three days during Jan/ Feb. 1gallon/week in other months. This started in the 20/21 season but I still had heat. My first indication something was awry was the largest radiator on the 1st floor with a 63 EDR took more cycles to heat up and the vent kept expelling air despite trying several new ones. Another, a 19 EDR radiator on the second floor didn’t heat at all until I put a vent on its riser.

This continued during the 21/22 season and by April things devolved to the point only the radiator closest to the boiler got warm and the boiler stopped cycling -neither on pressure nor temp. The 0-5 psi gauge reached 0.2 after the boiler ran for 30 mins and then I could hear the two main vents start venting. When the boiler was healthy, steam would reach the Big Mouths in 7-8mins from cold start and the boiler would run at 1.2 and cut out at 1.8PSI. I drew about a quart a week to flush the sediment October-December then less thereafter.

In the 20/21 season two plumbers tried but failed to find any leaks in the system. Last month I talked to a third one who listened to what I had done to test for leaks including flooding the boiler and looking for steam going up my chimney. Without saying a word he took out his cell phone and stuck his hand in the boiler and took a video of the sections. As I fired up the boiler, he read the boiler rating, waited for 2.5 mins, then stuck his cell phone and took another video. He then invited me to stick my hand just below the chimney and feel how wet the air felt: almost like steam. He concluded the boiler was leaking, then went back to his cell phone and played the second video and we could see water boiling off on two sections.

The tale doesn’t end there. I asked him if he installed boilers but he doesn’t. He does annual checkups on them for his customers. He told me he was a plumber who specialized in finding leaks. His father owns the business. He refused to charge me for the visit but hoped I’d hire him to do the annual check up for my new boiler. I opened my fridge and gave him a six pack of Sam Adams. We both smiled.

I sent both videos to Crown, they said the boiler has a 12yr warranty for the block, and while they typically like to see evidence of a cracked boiler with the Jacket off, they would honor their warranty with videos and additional near boiler piping pics I sent. The one year proration is not worth the hassle for filling out the required collateral for an installer.

Next, I talked to 33 boiler installers within a 25 radius of my house using deduplicated lists from Con Ed, Peerless and WM websites. Filtered them on the phone down to 8 and had those do a site visit after which I have 2.5 left who are clearly steam men. All 3 wanted to know why I thought the boiler was cracked, they fired up the boiler, checked the main vents and saw the videos. I told them about the wet steam causing gurgling radiator vents. Neither asked why I had a single take off on the header while there are two mains with returns joined in the basement. They failed to notice the bullhead tee. So I showed them. Two of them took radiator measurements and photos for sizing. The .5 person asked me the EDR load but seemed reticent to do it himself, otherwise he seemed fine at explaining the piping he’d do as well as the evils of oversizing. I have eliminated him at this point.

Sorry for the long rant. There are far accomplished raconteurs on this forum. My EDR is 270 the boiler was 357. I will doubtless have more opportunity to harness the expertise here as I proceed with a new install and a contract. I have will be using the Peerless 63-03 with a single 3” riser and the rest according to their specs. The two bidders have been given free reign to propose any unit at this point.

Thanks to everyone.

https://www.dropbox.com/s/w9dutgrasezdr2z/coldboiler.mov?dl=0

https://www.dropbox.com/s/zi1jjo1d92e1qac/runningboiler.MOV?dl=0

mattmia2

Isn't that just condensation from the hydrogen in the fuel turning in to water vapor and condensing in the cold oiler sections?

I would invest in a king valve and a valve on the return on the new boiler so you can valve it off for diagnosis in the future.

Are you sure the boiler is firing at the correct rate? If something has gone wrong with the regulators or something like that so it is underfired it won't make enough steam to fill the system. Did anyone clock the meter?

If you are leaking enough steam that you can't pressurize the system when you could before, you should see a leak when you flood it especially if you leave it for a day or 2.

Steamhead

Looks like a definite leak to me. That 63-03 should serve you well.

Jamie Hall

That much usage is a leak. Not a very big one -- but a leak. I expect you may have found it...

PhilKulkarni

Thanks gentlemen. I checked to make sure the boiler was firing at the rated heat input by first turning my gas water heater off as well as my kitchen stove. I then fired up the boiler and measured 2.2 cu ft/ min on the 1/2 cu ft/rotation gauge on the gas meter. At 1030 BTU/ cu ft this comes to 135,960 Btuh, very close to the rated 138,000Btuh of my boiler.

I had unscrewed my Big Mouth on the end of shorter dry return and flooded the boiler till the water came out of the nipple. Kept it flooded for 3 days and the burner tray was dry. Then I flooded it to the top of the sight glass then waited for three days but the level had not moved. The only explanation is the crack is small when the boiler sections are cold but widens and the burner flashes the water to steam before it can drip down. While not apparent in the video, the boiler makes a scalding sound, like when you put some water over a hot pan.

Steamhead

I think you've got it.

ethicalpaul

Nice job finding good candidate installers. FYI you won't need a 3" riser, you can run 2" from boiler, to and including the header, and to and including the main(s).

3" won't hurt, but it won't help either. Peerless doesn't under-specify its piping.

PhilKulkarni

@ethicalpaul, I have seen your setup with a 63-03L produce dry steam perfectly with a 2” riser. Clearly you have the empirical evidence. My operative rationale for a 3” riser comes from the table shared on this site that shows the various riser velocities as a function of riser and header dia for the Peerless 63-03. With a single 3” riser, the steam velocity, assuming this table is correct, is 14.2ft/sec vs 31.3ft/sec for a single 2” riser. The cost difference of the fittings for the larger size from the SupplyHouse site is around $60, which is negligible, and the labor is about the same. So, why not shoot for the slower velocity?

ChrisJ

PhilKulkarni said:

@ethicalpaul, I have seen your setup with a 63-03L produce dry steam perfectly with a 2” riser. Clearly you have the empirical evidence. My operative rationale for a 3” riser comes from the table shared on this site that shows the various riser velocities as a function of riser and header dia for the Peerless 63-03. With a single 3” riser, the steam velocity, assuming this table is correct, is 14.2ft/sec vs 31.3ft/sec for a single 2” riser. The cost difference of the fittings for the larger size from the SupplyHouse site is around $60, which is negligible, and the labor is about the same. So, why not shoot for the slower velocity?

Velocity is moot if there's no water in the piping.
The difference between doing a 2" header and a 3" header is only $60? It's been 11 years since I did mine but I recall the difference between 2" fittings and 3" fittings being astronomical. I still did a 3" header but it hurt.

Does that include everything and do you have wrenches that will work with 3"?

The Steam Whisperer

I don't think we know yet if this if one or two pipe. It can make alot of difference to boiler sizing. Also, on this small model, we just use a 3inchx 12 inch nipple coming up out of the boiler to kill velocity and then drop to 2 inch for all the header.

PhilKulkarni

I would be doing exactly as the Steam Whisperer says. Use a 3” riser, 24” tall, with a reducing elbow going into a 2” header. The cost differential is for the 3” nipple, 3” union and a reducing elbow. The 2” set up requires a bushing on the 3” tapping that I don’t need. Even if I was by a factor of 2 for these larger fittings, it would still be insignificant. The only deviation from the Peerless spec is the 3” riser.

ChrisJ

PhilKulkarni said:

I would be doing exactly as the Steam Whisperer says. Use a 3” riser, 24” tall, with a reducing elbow going into a 2” header. The cost differential is for the 3” nipple, 3” union and a reducing elbow. The 2” set up requires a bushing on the 3” tapping that I don’t need. Even if I was by a factor of 2 for these larger fittings, it would still be insignificant. The only deviation from the Peerless spec is the 3” riser.

I checked the prices just to make sure my memory wasn't playing tricks.

A 3" nipple into a reducer and then all 2" sounds like a good idea for a boiler with dry steam.

AdmiralYoda

I didn't get a chance to read all the comments but if your EDR is really 504 which includes the derating of the recessed radiators...you may be able to get away with less.

That EDR=504 includes a 33% pickup factor to cover radiation losses in piping, etc. If all of your pipes are well insulated, including (and especially) the near boiler piping....you can get away with less. If your system is already well balanced and you don't mind adjusting air vent sizes to tweak it further, I'd be comfortable going down to a 10% pickup factor.

In addition to having good pipe insulation, the radiation in your house is likely larger than it needs to be...especially if you have tightened the building envelope. Your radiators probably rarely produce the full EDR the system is capable of, except maybe during the coldest days of the year or after a large setback.

A 10% pickup factor would be an EDR of about 417. Food for thought.

ChrisJ

AdmiralYoda said:

I didn't get a chance to read all the comments but if your EDR is really 504 which includes the derating of the recessed radiators...you may be able to get away with less.

That EDR=504 includes a 33% pickup factor to cover radiation losses in piping, etc. If all of your pipes are well insulated, including (and especially) the near boiler piping....you can get away with less. If your system is already well balanced and you don't mind adjusting air vent sizes to tweak it further, I'd be comfortable going down to a 10% pickup factor.

In addition to having good pipe insulation, the radiation in your house is likely larger than it needs to be...especially if you have tightened the building envelope. Your radiators probably rarely produce the full EDR the system is capable of, except maybe during the coldest days of the year or after a large setback.

A 10% pickup factor would be an EDR of about 417. Food for thought.

I agree,
Except as @Steamhead said you can downfire the burner on an oil fired boiler.

PhilKulkarni

Thanks everyone. Helpful comments. @ethicalpaul, good catch, I stand corrected. The 3” fittings are very expensive. The price diff. between using a 24” high 2” riser and a 3” riser is $218. I created 2 carts one with the 2” and the other with 3” fittings but didn’t realize that some items were still 2” in the latter and hence the diff came out lower. Having lived with a boiler that produced very wet steam, I think that extra spend is prudent. Here how I see the rationale:

With the same 2” header, the velocity of the steam in the header is the same whether I use a 2” or a 3” riser. on a 3” tapping. But I simply want to slow it down using a 3” riser and minimize the amount of water carried over into the header, however small it might be. I also get your point though- if no water leaves the tapping why worry about a larger riser size? Just insurance since my two previous boilers did.

To both @chrisj and the Admiral, I’d like to examine if the 63-03 with the pickup might be oversized. So here is some piping info. All 2” mains total 54 linear ft. They have 0.5” fiberglass insulation and for the most part are exposed to an ambient of 50F or higher being in the basement or a semi heated crawl space. The wet returns are 37’ with the same insulation. The risers are in uninsulated walls and have asbestos insulation whose condition I don’t know. This is 1924 three story townhouse with similar units on either side. Thus two sides of the house are heated by neighbors. The rads are on the front and back. 7 of the 10 rads are on
1 1/4” risers while 3 are on 3/4”. Of the three, two are 16 sq ft EDR each and one is 19. Do you think The pickup adequately covers the pipe EDR? One of the installer thinks the boiler would be undersized for a 2100 sq ft house. We both calculated the EDR load at 291 without derating the recessed Sunrads. I come out at 270 sq ft after derating them 10%.

I want to end by saying that the current EDR load holds the night temp at 68F and the day temp at 70F. Thank you everyone.

PhilKulkarni

I have two other piping questions for the experts here. My single 2” main is split using a bullhead tee. The pic is posted on this thread. Is it essential to take it off, cut a section of the main to the right of the tee in the pic, thread it, then use an elbow at each end and create two separate mains. Can I get away without this extra work and continue using a single main from the header split by the tee for the new install? The cost is quite significant.

Also the two mains are pitched up from the boiler and one of the upward pitched section is 21’ long before ending in an elbow then sloping down to the wet return. Do I need a drip on this section? My pipes don’t bang.

Thank you.

mattmia2

PhilKulkarni said:

Also the two mains are pitched up from the boiler and one of the upward pitched section is 21’ long before ending in an elbow then sloping down to the wet return. Do I need a drip on this section? My pipes don’t bang.

Thank you.

Do the mains drain to the boiler or away from the boiler? If they slope down toward the boiler so that they drain to the boiler then you need drips before they drop down to the header.

There is also the possibility that someone changed the elevation of the mains at the boiler when they replaced the boiler at some point and they no longer slope the way they were intended to.

EBEBRATT-Ed

@PhilKulkarni

If you have two mains it's always better to bring them down to the header individually

PhilKulkarni

@mattmia2 the counterflow sections of the mains were there while the previous boiler was here. There were 2 strap type hangers that pitched them upwards even higher than they are now. They are broken with some parts still attached to the joists. I can have the installer replace them with clevis hangers to restore their pitch. Is 1/4” per foot the proper pitch?. I will include the drips in the contract.

Ed- if I can get dry steam in the header, will leaving the bull head tee the way it is make an appreciable difference? Surging and wet steam are two things that might happen get frequently mentioned. Looks like I have little choice.

Thank you.

ethicalpaul

That was @ChrisJ who did the research on the price differences. You are right in your response to me, there is no harm in it and I'm certainly no one to advise people not to spend extra money

PhilKulkarni

New boiler installed-almost.

This my new Peerless 63-03 install that is partially complete. The water feeder, the stat connection, the gas connection and a few other things remain. Yet, I would appreciate any feedback on a few questions:

The second riser is capped at the top, flush with the cover. Should the 3” nipple have cleared the cover by perhaps an inch and then capped or is it ok?

The 2” header with the 2 tees is 20” long at the point it connects to the equalizer. It has a 1/4” pitch towards the equalizer which may not be readily visible in the picture. Is that ok?

Skimming. The installer has the 1 1/4” skimming port reduced to 3/4” to attach a pipe since there is no space there for a 5g bucket. A 2g square bucket does fit between the back wall and the skim port but will mean more trips to the sink. I will ask him to install a shorter nipple, followed by the open tee for chemicals, then a ball valve, then a 2” nipple and lastly an elbow facing the wall. If the length of this contraption is too long, can I just toss in 2 Steamaster tablets and eliminate the open tee?

Still on the topic of skimming, only the 2g bucket fits below the 3/4” blow down drain tapping. However, there is space for a 5g bucket at the end of the tee where the feed water enters the boiler return and the hot water tank. That has a ball valve. Can I use this to drain the settled gunk? It appears to be at the same ht as the drain tapping, i.e. the lowest point. But I am not sure if this is the “mud leg”. Alternately, on the left side, there is a 2 1/4” tapping (shown opened) in the pic. Can I use this to drain the boiler and then close it off after the skimming is done?

The installer has budgeted 2 trips for skimming, but it does not appear to be his strong suite. I plan to run the boiler for a day since there were new 2” mains installed after ripping out the bullhead tee-more oil to skim off. Is running the boiler critical before the initial skim or should he skim first, run it and skim again?

Thanks in advance.

mattmia2

The heat is necessary to melt the oils. Maybe heat it to just where it begins to boil then skim it once run it a couple days, skim again, run it a week or so then skim a 3rd time. The more oil you can get out before it is steaming, the less that will get in to the system and the easier it will be to get the water clean.

The Steam Whisperer

I'd put in a 1 1/4 x 3/4 tee or 90 pointing down so you can get the benefit of a much wider skim surface when skimming.

PhilKulkarni

Thanks everyone. Very helpful.