Yet another boiler sizing question from a newbie...

Mikeyjawn

Newbie here – 

My wife and I  bought our first house in April 2014 (a 1910 bungalow with 1800 sq. ft.) knowing the steam boiler was/is on its last leg. We bought the house fully understanding it will be a fun project to live with steam radiant heat – it attracted us from the beginning. Oh yeah, it was a good price too (fixer upper – consider myself a

handy man). I also bought the house and bought into this system knowing this website and Dan’s books will help me get through any issues and enjoy warm and comfortable and unique (for Nebraska) heating. House has blown-in insulation in the walls, attic has 6”-8” of coverage, windows are original single-pane single-hung with aluminum storms outside.



So, current system is a Peerless 61-06 natural-gas/steam that’s less than 15 years old and is shutting off due to low water – this was occurring at least twice a day in April when it wasn’t very cold out. The homeowner had determined before the sale that it is a cracked section – I can hear it hissing while running and there’s no water on the floor. The water in the unit is also very rusty and I suspect the submerged section of the wet

return is very dirty and probably needs replaced



Piping: 2-2” take offs on the boiler into a 4” header, then 2-2” take-offs for the two steam lines. Two-pipe steam system, 3 or 4 radiators have Hoffman No. 40 vents (these will go away…), 70 foot-2” main has a Hoffman No. 76 at the end, 30 foot-2” main has a Hoffman No. 75 at the end, and the wet-return has a Hoffman No. 75 at the intersection between two sections of return lines; no insulation on mains or returns (this will be fixed before this season).  I never heard any water hammer or disturbing noises. Aside from relying on vents on the radiators and the lack of insulation on the mains the system seemed to function okay before shutdown this year so I am assuming near-boiler piping must have been done okay? I am going to try to get all of the traps cleaned/replaced as well as I am guessing a couple are plugged or non-functioning based on how the radiators heated. I shimmed up a number of radiators to get them pitched at least level if not to the drain side. All of the mains appear to have proper pitch (at least they are draining, I haven’t verified the inch/ft.). Flue is shot as well and I

don’t have a chimney cap so am hoping to get that in this year as well… and

studying to take the a major exam in October… and going to a wedding overseas

for two weeks… A lot to accomplish.



System has the following radiation attached – 7 total rads:

1st floor

Den 4 column/22”high/9 section – 36 sq. ft. (Hoffman 8A trap)

Liv Room 4 column/22” high/18 section – 72 sq. ft. (Hoffman 8A trap)

Din Room 4 column/22” high/13 section – 52 sq. ft. (Hoffman 8A trap)

Wat Closet 3 column/38” high/2 section – 10 sq. ft. (Hoffman 8A trap)

2nd floor

Studio 3 column/18” high/23 section – 52 sq. ft. (Sylphon trap)

Master Bed 3 column/18”high/22 section – 50 sq. ft. (Hoffman 8 trap)

2nd Bed 3 column/18” high/22 section – 50 sq. ft. (Hoffman 8A trap)

Total Radiation = 322 sq. ft. (or 77280 MBH)



The old boiler is a bit oversized (a Peerless 61-06 is rated for 121 MBH net and 504 sq. ft. ~56%+ oversized). There is only one spot in the house where a radiator was removed and the main is capped off – I doubt that radiator was a 150 sq. ft. unit, so this system has been oversized for some time.



As I do my research I am finding the following units are within the size range for the current radiation:

322 sq. ft. current radiation (77 MBH net)

Peerless 63-03 308 sq. ft. (74MHB net)

Well-McClain PEG 40 325 sq. ft. (78 MBH net)

Burnham IN5 358 sq. ft. (86 MBH net)

New Yorker CGS50A 358 sq. ft. (86 MBH net)

Peerless 63-04L 383 sq. ft. (92 MBH net)

 

Okay, so my question: most every post I find on this topic says to oversize if you are close to a boiler size, but I have seen a few people say you can go down a bit. If I need 322 sq. ft. can I safely undersize by 4% (Peerless -03), should I oversize 1% (WM PEG 40), 11% (Burnham/New Yorker), or 19% (Peerless -04L). Since I have a Peerless and am ‘naively’ assuming the piping is correct (given the current system is working well) it

looks as though another Peerless would go back in quite well with minimal

changes (less cost), especially given the orientation of piping is the same

(RT-side for return, two take offs for output, height of unit is the same, etc.) and that could save some work during the install – I fully realize that every boiler requires the proper piping and whatever must be changed will be at this time, I am just trying to be optimistic that some piping may be re-usable. Of course the price is a factor as a few hundred dollars helps buy a fair bit of insulation and traps, but I will ultimately do what is right and what is necessary When I look at the numbers it seems like the Well-McClain is perfect if I plan to add nothing in the future (again, I haven’t lived in the

house through a Nebraska winter like last year so I don’t know if the house is

warm enough – the insulation/windows along tell me it’s probably okay), and the

Burnham or New Yorker would be a better fit given they have extra capacity (in

case I want/need another small radiator installed) but are not too oversized.



Is a 4% undersized even possible to consider? Is 10% too much oversized? Is 20% too much? Is 1% oversized just taking too much of a gamble or is it just right? If I were to pull the trigger today I would go with 1% oversized and if I ever needed heat in different parts of the house I would consider trying to switch out a larger rad or two and add a small one where needed.



Thank you to any and all. I hope to not to be a troll and to be able to add my two cents in the future when possible.

BobC

It looks like a vapor system

Vapor systems are best run at very low pressure - under 1 PSI. If the house is reasonably well insulated and all the piping in the basement gets insulated with 1" rigid fiberglass you can undersize the boiler. The sq ft of steam rating assumes a 33% pickup factor, if all the pipes are insulated you probably don't need the full 33%.



You have to find a good steam main to look at your system and see what he thinks, your photo does not show enough detail to be sure of what you have. take more photos from different angles so we can see what you have to deal with.



The skill of the installer counts more than anything else in steam systems. He has to make sure all the piping has the correct slope and that the near boiler piping is done correctly. All the traps have to be checked to be sure they are working. The system should have a vaporstat, not a pressuretrol to control the pressure.



Bob

JUGHNE

Bungalow

Does your 1800 ft count both floors?  On picture #3 does the radiator supply valve have graduations to perhaps indicate an orifice valve for inlet operation?  On your "newer" risers/headers is there a concentric 4 x 2 bushing connecting to the older horizontal header or eccentric? 

In 1910 my guess is that there was no insulation in walls and maybe a few inches of zone lite dumped into the attic (at best).  Probably wood storm windows over single panes.  ( Probably better than aluminum combos).  So if that is the situation you may have more rads today than actually needed.  Are your wet returns under the basement floor or can you see all of them above?

Mikeyjawn

More pictures of my potential vapor system

Thanks for the replies. Vapor system sounds exciting. More learning to take place to understand how this works.



JUGNE - the house is 900 sq. ft. on each first and second floors; all wet returns are above the floor and visible; the rad valve is Dunham packless that simply indicates "On/Off" on the top and it's currently stuck - one other large rad has a similar valve and handle on the inlet, all others are the black knob and valves on the inlets. As for concentric vs. eccentric bushing in the 2" to 4" header connection I assume it's concentric (based on my understanding of these two types of fitting - pipes are centered on each other).



BobC - here are some pics. Not sure what helps. More of the near boiler piping and hartford loop; a few of take offs to the rad lines, one of the plugged take off; the main vents. More than willing to keep taking as many pics as it takes.



Thanks!

Steamhead

First thing to do

is change the Hoffman vents on the 70-foot main and the return line to Gorton #2 vents, which will vent a lot faster than the Hoffmans. The 30-foot main can keep its Hoffman. This should get steam out to the ends of both mains at about the same time, and the longer main will heat up a lot more quickly.

Mikeyjawn

Venting, orifices, traps, and the boiler size

Steamhead, thanks for the info on the main vents - sounds easy enough.



As BobC stated this system should have a vaporstat installed (and I am assuming a low pressure gauge on a pigtail?) - am I correct in understanding this should be the 0-16 oz vaporstat? Reading more about the vapor systems, people say they are best off with either an orifice on the inlet to the rads or the traps on the outlet, and as you stated I  need to make sure the traps are functioning - does this type of system benefit from installing orifices or is it 6 one way-half a dozen the other given the traps are already there and functional? If a trap needs to be replaced/repaired would it be better to eliminate that trap and install an orifice?



So far it sounds like when a system like mine is properly insulated, properly vented, and properly piped it can be slightly undersized and still work given it's low pressure - am I getting the basics here?



Thanks again!

Fred

Header size?

It looks like the newer portion of that header is 2 to 2.5 inch pipe that matches the risers. I would think you'd get much better steam flow (lower the steam speed and dry it out a little more if you could increase the diameter of that portion of the header to match the older section (looks like 3 or 4 inch pipe)

Jamie Hall

On the orifice vs. trap question... and so on

it really is six of one and half a dozen of the other.  Either way, they need to be right.  Traps have some real points (one reason why they are so common!) in that they either work or they don't, and if they are working properly then you have no problems with getting the right steam flow into the radiators.  Orifices, on the other hand, have no moving parts to fail, so if the pressure is right, they will always work -- once they are properly sized for the radiator.



Take your pick...



Traps, I might add, can last a very very long time if they aren't abused -- all the traps on my system are original (about 85 years old).  A couple of them have failed open, which would be a nuisance except that I also have Hoffman valves, and the solution is to set the valve to meter the flow, just like an orifice would.  Which works just fine.  I could replace the failed traps but, honestly, I'm too lazy and too cheap!



You will want a 0 to 16 ounce vapourstat.  Set it initially to cutout at 12 ounces and back in at 6.  You can dial it down some if you find it works better that way.  A low pressure gauge (it can be on the same pigtail) is a big help to make sure that the 'stat is working the way it should; sometimes they do need a bit of calibration.  One other type: a snubber (look at http://www.omega.com/pptst/PS_SNUBBERS.html for examples -- must be steam rated) will help to stabilise the vapourstat and prevent it from turning off prematurely on brief blurps and surges.



Keep the standard pressurestat (wire them in series) as a safety backup.

Mikeyjawn

Snubber on vaporstat

Jamie - thanks for the tip on the snubber. A search for the setup shows me some very nice assemblies. I see the basics on getting the low pressure gauge up high enough to avoid water bouncing up into it. Also the shut-off valve on certain parts of the assembly to be able to isolate the gauges. Next up will be looking at the series wiring between the vstat and the pressuretrol. Seems pretty straight forward.

As for the traps versus orifi (plural?) I am going to stick with what I've got and get the traps working right. I suspect at least one trap is not flowing properly as that rad never fully heated last spring when I ran the system. That rad was also pitched horribly toward the inlet so it may have a bit of water and crud in it - it's in the living room too. That will be fun to take apart to clean/replace if necessary. I like the idea of the orifice and will likely migrate that way in a few seasons once I learn more about this system in operation and how it wants to work best.

Thanks again!