old boiler vs new boiler, why so different, steam capacity

GW

I'm looking at an old house, current original one-pipe steam boiler (I'd guess the 1930's) is running at 3 GPH oil. The boiler is a monster, coal to oil.

Rad numbers are looking like 760 EDR, more like 2 gallons.

Do i need to overthink this at all? maybe the oil guys ran the old beast higher gph becasue of its sheer mass and scale all the cast and water to heat up?

PS the owners did remove the living room rad(s), but still, there is a big diff between 2 and 3 gal of input.

Thanks, Gary

BobC

That was probably done when oil was ten cents a gallon (I bought oil in 1970 for 13.9 cents/gal) and nobody wanted to chance under firing a boiler. I'd bet that 760 EDR was to keep the house at 70 with some windows open for fresh air as well. Any insulation in the house?

Be interesting to convert that to a one pipe vacuum system.

Bob

GW

Bob the people are selling and they were encouraged to get a new boiler installed by their realtors; they will be doing just the basics. I didn't ask about insulation; I suspect there is some based on what their fuel consumption is (2200 gal or so)

Paul48

When they converted it from coal to oil, they sized the burner to the firebox.

GW

Ok good to know!

Jamie Hall

Just to give you some idea of the difference -- when heat was originally installed in the place I care for, in 1930, it was steam, oil fired, with an immense boiler. And a Quiet May burner which used about 5 gallons per hour. Now it has a much smaller, modern boiler, and heats equally well -- on 2.75 gallons per hour.

ChrisJ

My neighbor's Redflash converted boiler is the same way, grossly oversized for the load. I personally think it was done to try and get the 40 gallons of water up to boiling faster but I really don't know. What I do know is the thing produces way too much steam for the load and yet still takes 40+ minutes to start steaming from a cold start.

Size the new boiler to the load according to your numbers, ignore the current boiler. I'd recommend aiming for a 15-25% pickup factor assuming all piping will be fairly well insulated.

The system will purr like a kitten.

GW

Great thanks, 1.33 just a bit big for an insulated system?. I've read shaving some off a while ago but always just used the 1.33

ChrisJ

GW said:

Great thanks, 1.33 just a bit big for an insulated system?. I've read shaving some off a while ago but always just used the 1.33

You'll get a lot of arguments on this.

I'm currently running 1.10 on my own system. I think Jstar was aiming for 1.15 typically.

The Steam Whisperer has run negative pickup factors. I wouldn't recommend it until you get a hang of balancing a system running super low pressures, and you need to do a heatloss.

With a 15-25% no need as you'll get plenty of steam to the radiators, you'll just need to vent them on the slower side.


I believe @Hatterasguy has done a much larger system recently.

Steamhead

Coal-fired boilers were typically oversized so people wouldn't have to shovel coal and ashes so often. When the oil guys came along, they fired these boilers to their maximum rating. When it came time to replace these boilers, some people just put in the same size that was there, figuring if that size worked for so many years it will still work.

That's why we still have so many oversized boilers.

GW

15-25 got it. No ins go 33.

ChrisJ

Hatterasguy said:

GW said:

Great thanks, 1.33 just a bit big for an insulated system?. I've read shaving some off a while ago but always just used the 1.33

Don't use 1.33 with a fully insulated system. 1.20-1.25 is plenty.

If you really have some gumption..................you can get down to 1.1 like ChrisJ..........but the time factor to balance the system goes up massively and you run the risk of living at the premises.

An interesting tidbit:

The use of a large drop header resulting in very dry steam, causes the entire system to behave like the pickup factor disappeared. It's quite strange but at least four of us have witnessed this phenomenon.

The apartment building has well over 1.33 and yet, it develops no pressure. Striking.

What happens if the system runs for a really long time?
It must develop pressure then. Even mine would go up over time, after an hour and 20 minutes it hit 1.5 PSI one time in it's life before I downsized the boiler.

Now, with the 10% pickup factor it seems like it can run forever and never exceed 0.75" WC. I've got the Ecosteam switch to shut it down for 10 minutes if it hits 1 ounce and that never happened yet, even doing large recoveries.

ChrisJ

Hatterasguy said:

It's on the Tekmar 279 as you know.

The longest it can possibly run is 58% on the design day. 35 minutes and it shuts down for the next 25 minutes.

No chance of of running for sufficient time to even get the data that you seek unless I do it manually and cook the tenants................

Oh, there's nothing I love more than letting the house drop 10F on a cold night and then doing a long 1+hour recovery just because I can.

BobC

A buddies dad had a old 3 family house that he rented out. He got a call from the 2nd floor tenant about frozen pipes in the kitchen so he went to investigate.

he found the 2nd floors boiler stone cold (tenants paid for their heat) and knew the tenants were away for at least another week. After making sure no one was home he let himself in and found a 25w bulb within an inch of the thermostat that kept the boiler from turning on.

After moving the bulb and getting the heat to come on he was able to thaw out the pipe 9lucky there was no pipe damage. He left the heat set on 65 and later told the tenant if it happens again your gone. He included a clause in the lease that heat MUST be kept at 62 or above at all times.

Tenants will find away to trick thermostats, you just have to find a way to find out before damage occurs or fuel bills skyrocket.

Bob

PMJ

Hatterasguy said:

It's on the Tekmar 279 as you know.

The longest it can possibly run is 58% on the design day. 35 minutes and it shuts down for the next 25 minutes.

No chance of of running for sufficient time to even get the data that you seek unless I do it manually and cook the tenants................

Exactly. Control the run/off times and a bigger boiler is managed quite easily.

ChrisJ

That doesn't mean someone should intentionally install a grossly oversized boiler and then force it to run many short cycles.

PMJ

ChrisJ said:

That doesn't mean someone should intentionally install a grossly oversized boiler and then force it to run many short cycles.

Depending on your definition of grossly I would agree. But the closer you cut it the more critical things get and balancing can become a "living at the premises" only proposition as @hatterasguy points out. I have a friend who owns several steam heated apartments and in discussions with him it quickly became apparent how much easier it is for me as a live in owner to run a system than a landlord or residential contractor. Night and day kind of different.

So I would recommend to most to make sure the error was on the side of extra capacity. I believe it is way easier to handle issues associated with too much capacity than borderline too little.

ChrisJ

PMJ said:

ChrisJ said:

That doesn't mean someone should intentionally install a grossly oversized boiler and then force it to run many short cycles.

Depending on your definition of grossly I would agree. But the closer you cut it the more critical things get and balancing can become a "living at the premises" only proposition as @hatterasguy points out. I have a friend who owns several steam heated apartments and in discussions with him it quickly became apparent how much easier it is for me as a live in owner to run a system than a landlord or residential contractor. Night and day kind of different.

So I would recommend to most to make sure the error was on the side of extra capacity. I believe it is way easier to handle issues associated with too much capacity than borderline too little.

Remember my number of 15-25% is extra. I feel 33% is too much for most applications, at least residential applications.

0% is likely too difficult or risky for most guys and 10% is likely workable but may be too difficult to balance. 15-25% I think gives a nice amount of room for error and tweaking.

Now if I could get the hang of grinding my own hamburger meat.....

PMJ

Hatterasguy said:

PMJ said:

Exactly. Control the run/off times and a bigger boiler is managed quite easily.

Got to be a bit careful with a blanket statement.

If the radiation is much greater than the heatloss, a big boiler relative to the radiation is never a problem. The boiler might only run 58% on the design day (ala the apartment building).

But, if someone, by some miracle, sized the radiation properly to the heatloss, and a "proper" boiler needs 100% on the design day, you can bet that an oversized boiler is absolutely going to give you problems.

The pickup and piping factor isn't a blanket 15-25% in all situations. You can be cavalier with the pickup factor if the radiation is quite a bit oversized..............not so much if it closely matches the heatloss (an admittedly rare phenomenon). In that situation, where the boiler is going to be running for close to 100% on the design day, you had better keep the pickup factor down below 20% and might even consider 15%.

Seems to me that if the installed radiation is perfectly matched to the heat loss on design day then that same radiation is significantly oversized for an average day. So all installed radiation out there is always oversized for the actual heat loss being faced at any point in time because design days never occur. And one way or another all control systems simply reduce the total boiler run time to match the heat loss. A bigger boiler will just need to run a smaller % of the total time.

Charlie from wmass

If 790 is the edr of the radiators with out adding a pick up factor use a Weil SGO8 down fired a bit. If that included a 1.33 pick up factor remove it and pick the next boiler to that, which would be a SGO6 down fired a bit.

GW

Yes that was the rad total edr.

I've always liked the peerless, EC series, I've done a bunch of Utica peg for our typical 2, 3 and 4 section gas.

Charlie from wmass

Weil can be converted to gas without affecting the warranty. I would not install uticas once I saw the insides of them. There is a reason why most guys in the valley install them and quality is not it. Do a side by side comparison some day.

GW

I'll see what willy webb sells the Wm for

Charlie from wmass

Lots of people sell weil

jumper

An explanation I heard is that coal boilers absorb more radiant energy from burning coal than from burning oil so conversion burner is upsized. Also there's an issue with blower moving hot gasses through boiler too fast.

PMJ

Hatterasguy said:

PMJ said:

Seems to me that if the installed radiation is perfectly matched to the heat loss on design day then that same radiation is significantly oversized for an average day. So all installed radiation out there is always oversized for the actual heat loss being faced at any point in time because design days never occur. And one way or another all control systems simply reduce the total boiler run time to match the heat loss. A bigger boiler will just need to run a smaller % of the total time.

The problem occurs near the design day when the boiler percent operation is above 75%. Now you have problems with an oversized boiler. Since it is running for an extended period without much off time, the system never cools down and the oversize cannot easily be managed.

The installed radiation is oversized for most of the year and might be oversized on the design day. But, not all systems are oversized in terms of radiation and these will absolutely get into problems with an oversized boiler.

That's just it. The too big boiler would never run 75%. My boiler is way too big. When they replaced the coal one in the 1950's they went way big as is being talked about in this thread. My solution is that my control won't ever allow it to run more than 50% of the total time(10 min on/10 min off). And 50% easily gets it done at -20+F with no insulation in the house - the coldest days around here in the last 25 years. As far as I can tell clocking the gas meter the darn thing is even down fired 25% from the plate. I'd say it is way too big. I just don't run it much and what I do run is spread out in even firings. Ultra low pressures and no problems.

I'm not recommending that anyone go way oversized. I'm just saying that being way oversized can be managed if you find yourself in one of these situations like I did. Undersized can't be fixed.

PMJ

Hatterasguy said:

PMJ said:

I'm not recommending that anyone go way oversized. I'm just saying that being way oversized can be managed if you find yourself in one of these situations like I did. Undersized can't be fixed.

If your installed radiation is 200% of the heatloss, it's easy to manage the big boiler in exactly the way you noted. Just run it 15 minutes on...............15 minutes off..........on the design day. It would never get into problems.

But, if the installed radiation is 125% of the heatloss, the same approach will not work.

Actually, undersized can be fixed if you vent the rads very slowly. In theory, you can make the system appear as a tiny fraction of itself. i wouldn't attempt it myself, however. Balancing it would be near impossible.

You are totally losing me here. By undersized I mean a boiler that cannot produce the steam required to match what the building is losing to the outside running 100% of the time. This cannot be fixed by venting.

Heatloss is a variable - different every day of the heating season. The colder it gets outside the heatloss goes up and the % the installed radiation is of the heatloss goes down. In your two examples the same boiler would have to run the same total time to heat the building. The rads would simply be fuller in the 125% installation than the 200% installation.

We had this discussion before in another thread I think. The output from radiators is variable not constant. In a well run system they are varied amounts of full with steam depending on the conditions.

Charlie from wmass

Thinking about it, I think my experience with undersized boilers they were sized below the heat load of the buildings, not just undersized for the system. Each of these cases lead to extreme fuel usage, both with gas and oil fired systems.

ChrisJ

Charlie from wmass said:

Thinking about it, I think my experience with undersized boilers they were sized below the heat load of the buildings, not just undersized for the system. Each of these cases lead to extreme fuel usage, both with gas and oil fired systems.

And has been said before, and the horse is now hamburger from being beaten so much, that only makes sense if the room with the thermostat didn't get heat but other rooms were overheating.

jumper

Charlie from wmass said:

Thinking about it, I think my experience with undersized boilers they were sized below the heat load of the buildings, not just undersized for the system. Each of these cases lead to extreme fuel usage, both with gas and oil fired systems.

Why? Except for especially cold days,the undersized boiler is closer to heat load than one designed for ten below zero.

ChrisJ

jumper said:

Charlie from wmass said:

Thinking about it, I think my experience with undersized boilers they were sized below the heat load of the buildings, not just undersized for the system. Each of these cases lead to extreme fuel usage, both with gas and oil fired systems.

Why? Except for especially cold days,the undersized boiler is closer to heat load than one designed for ten below zero.

The only reason is because the room with the thermostat was starved for heat. Otherwise, it makes no sense.

Get steam to that room first and leave others chilly and suddenly fuel usage drops big time.

The energy doesn't magically disappear. It went somewhere and it wasn't to what controls the boiler.

Charlie from wmass

The cases I have dealt with the boiler ran ridiculously long cycles without satisfying the thermostat. It also was like a mobile where as they got steam to a cold room it robbed it from an unexpected room.

jumper

When TRVs came out for two pipe steam,a concern was short cycling. If the owner invested in a lo-hi-lo burner,burner ran on low most of the season. At least in Toronto,Canada. I don't have information about fuel consumption,but common wisdom (which I still don't understand) was that steady heating is more efficient than heat up cool off cycle.

Charlie from wmass

the idea of steady heat is you are inputting heat at the rate it is leaving the building. More like highway cruising as opposed to start and stop driving. It takes a certain amount of time to warm all the system parts and the heating fluid to working temperatures. This is how vacuum can save fuel. It allows for the heat output of the heat emitters to vary according to the required heat loss for the current weather. Vapor systems can run from deep vacuum in the shoulder seasons to moderate pressure in the depths of winter.

PMJ

Charlie from wmass said:

the idea of steady heat is you are inputting heat at the rate it is leaving the building. More like highway cruising as opposed to start and stop driving. It takes a certain amount of time to warm all the system parts and the heating fluid to working temperatures. This is how vacuum can save fuel. It allows for the heat output of the heat emitters to vary according to the required heat loss for the current weather. Vapor systems can run from deep vacuum in the shoulder seasons to moderate pressure in the depths of winter.

Steady is the correct word to describe how most of our systems were originally designed to run as the coal fire couldn't be turned off. Amazingly sophisticated devices were designed to damp the fire to produce only the steam required to match the heat loss off the building in real time.

The switch to start/stop has been a significant step backward from the control aspect of things - and I would argue has hastened the demise of steam as a residential solution. And perhaps the biggest negative aspect to each and every stop in current systems is that the forward flow of steam to the rads stops immediately when the burner goes off and things then go backwards. Air enters and fills the rads and then the mains cooling them down. Each restart requires pushing all the air back out and reheating significantly more than would be required had the air not been allowed to reenter in the first place.

Anyone with a two pipe system should consider taking the pretty easy steps required to put a stop to this back and forth operation and just keep most of the air out altogether. You will be surprised how much more even the heat is. During the off cycle the steam in the mains continues forward to the rads, and not only that it will flow more to the rads that are condensing steam the fastest( the colder places). When this happens each and every cycle it evens out the entire house a lot.

Jamie Hall

There were indeed some very sophisticated devices -- many of them in the Rube Goldberg/Heath Robinson school of engineering -- to control the heat output of coal fires. Mostly if not entirely based on pressure. They worked remarkably well.

There was a problem. On anything except pretty close to full open, the air/fuel ratios were ... odd, to put it charitably, and the efficiencies were pretty horrible.

Like so many of these things, though, if one is willing to put up the cash there is no reason why an oil or gas burner system can't be built to maintain the correct air/fuel ratios (using a lambda control) over a very wide range -- 10:1 is trivial for aircraft gas turbines, for instance. But is it worth it?

A vapour vacuum system, though, with the correct vents (which close and hold vacuum) is a very good approach, though.

PMJ

Jamie Hall said:

There were indeed some very sophisticated devices -- many of them in the Rube Goldberg/Heath Robinson school of engineering -- to control the heat output of coal fires. Mostly if not entirely based on pressure. They worked remarkably well.

There was a problem. On anything except pretty close to full open, the air/fuel ratios were ... odd, to put it charitably, and the efficiencies were pretty horrible.

Like so many of these things, though, if one is willing to put up the cash there is no reason why an oil or gas burner system can't be built to maintain the correct air/fuel ratios (using a lambda control) over a very wide range -- 10:1 is trivial for aircraft gas turbines, for instance. But is it worth it?

A vapour vacuum system, though, with the correct vents (which close and hold vacuum) is a very good approach, though.

With fires that literally can't be turned off, there doesn't seem to be much point in discussing efficiency. And anyone living when coal was the primary fuel source for home heating will attest to the horrible dirty air conditions with all those damped down little fires.

Sure oil and gas can be modulated. But I would be quite sure it isn't worth the cost in residential heating. In fact, I have seen articles claiming that hi/low cycled operation even at the commercial level will beat modulation by 15%. Some say that modulation is only worth it when very tightly controlled pressure for a process is required.

The point I am making is that letting air back into a steam system is basically running it backwards. As what steam there is in the system collapses it is chased by air back to the boiler - the exact opposite of what we are trying to do when we heat. This was never an issue with a coal fire (though at very high cost to the environment). But on the steam side of the system inside the piping it was better. A system with a cycling boiler and natural vacuum between cycles is at least in forward motion all the time. I didn't expect things would improve as much as they did when I went ahead with it. It is too bad that it isn't easier on one pipe systems. But if I had one I would try it.

jumper

Heating coal was clean. Washed anthracite for houses. How much could one save using less expensive power coal?