New boiler size

mark ransley

I have a 1955 Kewanee Ng 2 pass heating 12 units its one pipe steam. Its time to plan a replacement but I think I am oversized but dont know. I will be putting on a foam flat roof of R 30 I hope. Windows are new dual pane. I am basing my question on buiding temp rise I observed and new insulation. Gas bills are excessive.

Several days ago boiler failed to run all night, I started it and kept it going 1 hr near continualy at about 2 lb pressure. It was a cold boiler and apts were 62f. It was 15f out and in one hour apts were 7f higher.

With that fast a rise in temp isnt my boiler oversized. But it does in Chicago go to -22 without wind chill in the past and can someday I bet hit -25 without wind chill.

What would be the best and most efficent replacement, thanks.

Big Ed_4

Steam

If you are replacing the radiation in the building then you size the radiation to the heat loss. Then size the boiler to the radiation. If you are not changing the the radiators then you size the boiler to the existing radiation. You need enough steam to fill the system. The installer will need to measure the EDR of the uninsulated system.

mark ransley

I dont understand why I cannot downsize boiler a bit. In HW and forced air you go by a heat load calculation. Here in the midwest Chicago oversizing heat systems was normal when they were well built 70 years ago, of course you calculate ductwork or HW radiator capacity.

If I go down 10 % to 1,000,000 Btu with all the extra insulation I have what I see is a more efficent system not cycling as often and running at higher peak efficiencies longer. It will still fill radiators with steam I believe, but save alot in fuel.

For my forced air at a home I downsized from 110,000 to 47000 btu, and for another home HW boiler heat we downsized 10% and both still only run 60% of the time in Chicagos coldest days. Ok Steam is different, but its still heat and cycling to often which equals low efficiency

7f hr raise at 15f outside on cold boiler and building. Is to much in my basic non professional learning to be efficient, my other types of systems do maybe 2-3f an hour raise.

Big Ed_4

The turn of the last century homes were designed to heat with the windows open. So they needed huge over sized radiators to over come the heat loss of the hole in the wall. The Spanish Flu , as it where called was killing people around the world at that time period . And all they know was that you can catch it from "Bad"air . They were deathly afraid of closed spaces and sleeper with the windows open. It was all fresh air heating in design , If you can afford it.... Check the roofs on that time peirod mansion for the vented copula...

Yes you are right , efficancy would increase if you size the whole system to the new load . You can install a smaller steam radiators to meet the lower heat loss. But if you keep the old radiation , with steam you need to produce enough steam to fill the system. If not the top floors and wings will not heat up.

The uninsulated system is rated in EDR. One EDR= one square foot of exposed surface area. The square foot rating output of the boiler should match the uninsulated square foot of the system.

Hot water and warm air are not the same animals...

mark ransley

Now the ends of the 100 ft apartment overheat big time, I need gorton 4 rad vents and some in the middle Gorton D, it still seems I have room to go down 10% in Btu or more. I could always reverse venting if it was smaller, I insulated pipes double over asbestos.

Big Ed_4

You most likely can down size....

....smaller then 10%. But you don't want to guess. Dan sells a book here called "EDR" Every Dam Radiator. He compiled just about all of the radiators that where made over the years . I use the book , in it is the sizes and EDR of the radiators listed. From there you can calulate what size boiler is needed .. Other then that it would be a guess. You will be Suprise how small you really need.

Hint, to balance a one pipe system. You size the venting to the size radiator. Less is more in radiator venting. More is more on main venting. You want to charge the main first through the big main vents., then heat and fill all the radiators at the same time. Since steam will follow the least resistance, turn down the rad vents. Start off there but you have to open a notch on the top floors or additions. But have control for proper venting.

mark ransley

Ed, the book sounds good, what do you mean by nothcing floors? Thanks.

Mark Eatherton

Notch = click...

He's telling you to open the top floor rad vents a little more than the lower floors to balance out the flow of heat to the branches. Not notch the wood on the top floor :-)

Dead men's jargon, dontcha know.

He could have said skosh :-)

Correct me if I'm wrong Ed, don't want to put words in your mouth.

ME

Big Ed_4

You Know Me Mark...

..... I can make a wrench sing .....but just add dirt to my English .

Typing on my iPhone as I wait for this 60 year old Weil Mclane to reach limit.

JJ_4

My approach to downsizing...

I have a 1923 home that I am in the process of downsizing the one pipe system. What I did was a heat loss calculation (Slantfin) broken down for each room. My main room came back without any changes needed for radiation as I planned to have some of the heat from this room "available" to an addition (that has electric baseboard) via two 3x3 transfer vents at ceiling height (11 1/2 ft) for this purpose (and for evaporative cooling transfer).

However, I installed smaller radiators in the a bedroom, bathroom, and kitchen/laundry areas. I was lucky to have some extra radiators available to "fit" the sizes I needed...because I eliminated two small radiator locations all together and was able to reuse them in place of larger ones. I reduced my EDR to match the BTU requirements. I am also using vari-vents, which helped dial things in.

I have yet to replace the oversized boiler...that was most likely sized based on the original coal boiler(window open, flu preventing, sizing method). When I do replace I will be able to reduce the size by half or more.

No problems heating with this reduced EDR...boiler doesn't short cycle either...not sure why...maybe because the stat is in the main room where I have the most radiation and lots of solar gain. That is...during the day their is little call for heat due to solar gain, but greater call at night becuase of loss thru windows. Who knows...it works.

Supply House Rick

boiler replacement

here is an analogy to the boiler sizing situation. if you have a large truck, fully laden, it will take a certain size engine to get it up to speed on the highway. you can't do with a smaller engine, or it won't even move. however when it is at cruising speed, because the brakes are NOT dragging, and the driver drives at the right speed, you get economy.

in the same situation if you get a new boiler, sized to the total radiator sizes for the building, you will get greater economy because it will not run so long as the old one did.

when you are planning this out, get a vaporstat, and investigate a 2-stage burner[ which is the equivalent of the truck drvers gentle acceleration]. another economy feature would be LOTS of main line venting. don't be mislead that the rad vents can do this, they will waste fuel trying to sueeze the air out of inadequate venting.

if you have gravity now, keep it. i wonder how long a foam roof will last, do they have a warranty longer than 12 mos. i like pvc with peel and stick myself. the flat roof is the greatest curse ever foisted onto the building owner!--nbc

Supply House Rick

radiator downsizing

i wonder if changing the air vent location would downsize the radiator. maybe a higher location for the vent would leave more air inside resulting in a lower btu output.--nbc

scrook_2

because...

with steam, unlike hot water or hot air, you MUST supply enough steam to match the rate the radiators will condense it. If you do not, you will not develop any steam pressure and some radiators will not heat. It is heat delivery via change of state (gas to liquid) vs. change of temperature (hot water or air) that the differance. On the other hand, you do not want the boiler grossly oversized for the attached radiation either.

It does seen counter-intuitive at first I'll grant, until you think thru what's happening in the radiation, so don't feel bad for asking.

If you can (at reasonable cost!) replace the radiators with smaller ones, or disassemble and downsize the existing ones, you may be able to better mathc them to th ecurrent room heat losses, in which case you can then downsize your boiler, but otherwise...