undersizing boiler

Christian Egli

Thanks, Bob.

Notice how we say picking up steam is good? And in contrast, loosing steam is no good?

Like you, I find thinking fun. Keeping our brains at a rolling simmer and, sometimes, watching them boil over. That’s the Wall.

billygoat22

undersizing boiler

Had a question posed today. House has 32000 btu load, but 7 radiators coming out to over 130000 btu worth. No insulation on pipes downstairs, which ho wants to heat. One pipe system, counter flow.

Takes 45 mins now for system to heat up. I suggested adding main vents since was told there were none on system, only crusty radiator vents.(I haven't seen it in person) They're going to go with new boiler, flush out radiators and new radiator vents.

Was asked if you could do undersized boiler (by house load) rather than size of radiation, which is WAY too much. I said by edr, or you could have trouble. I don't expect you want to reduce size of rads, either.

I checked the search and didn't see too much on undersizing effects. Saw mention that boilerpro was doing some investigation into this. I expect the pickup factor and balancing would be an issue with undersizing? Going to check Lost Art and Leinhardt's now. Appreciate any input.

Bill Nye_2

You have to

You have to fill the radiators with steam for the radiators to heat. You can't fill 10 gallons of radiators with a 5 gallon boiler, so to speak. To fill 400 sq. ft. of radiation and piping , you need a boiler that can make 400 sq. ft of steam , does that make sense?

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Keith_8

I suspect

the area with the uninsulated pipe will be warm but thats about it. Chances are you can find a small boiler to match the true EDR. The boiler will be efficient and do the job.
Why not go into it expecting satisfaction?

That being said we installed an undersized steam boiler on a mothballed building a few years ago. A building without any occupants may be the exception, comfort is not the objective only freeze protection.

Keith

Matt_21

if the radiators are

steam, you have to size the boiler for the total load of all the radiators whether it is oversized for the house or not. if the radiators are the hot water type, you can size the new boiler for the actual load of the house.

STEVEN MARKS

7 radiators with a btuh load of 130,000?? Those must be some really big radiators. That would be an average of 18,571 btuh each or 123 EDR. Are you sure you sized the rads correctly?

billygoat22

I didn't goto the job, so didn't see the system yet. Was asked if you could get away with downsizing, which I answered "no, size to radiation, regardless".

The edr is estimated at about 400 sq ft. Was just wondering the effect on system.

I would submit a theorey that insulating pipes downstairs, and if the radiators had those restrictive covers, you could insulate part of the radiator with a ductboard material to "choke off" part of the edr making the radiator act like a smaller one. Perhaps this would help an existing undersized boiler work, assuming its big enough for the house load.

We'll be using a boiler sized for the radiation in this case. Wouldn't try a theory but on my own house, if I had steam.

Christian Egli

Radiation spoiler, a shiny new look?

Shielding the radiators to cover the half that is too big sounds like a good theory to me. After all there is no difference between a steam main and a radiator as far as surface radiation is concerned. I’ve never done it but I imagine loosely wrapping radiators with aluminum foil should already make a big difference.

You’ve got to love radiators!

I believe Boilerpro installs measured orifices in the valve that lets the steam into his underfed radiators. This is an easy way to go undersized, but it is only good for two pipe systems, it is just like adjusting a graduated valve.

The way I know steam, it has a knack for finding the coldest place in a system. That’s where it likes to chill and ultimately condense. That’s why industrial cooking with steam is best; no vegetable or piece of meat remains uncooked, however distant it is from the bottom of the pot.

The only hitch, steam won’t go condense wherever there is still some air left.

You can forcefully eject all the air but only with full boiler power matched to the radiation. Once this is achieved, you can assuredly go into lowered boiler output and still get good steam distribution throughout all radiators. To further keep the still air out, a vacuum vent is ideal. They were great with coal fires but their unflappability does not suit jittery gas and oil fires.

A great way to use grossly undersized boilers is by providing a mechanical method for evicting the air from the radiators. The steam no longer needs to bully its way around and with no squatting air, it can leisurely find the coolest place to chill out.

How do you police the air out of the way? With a friendly vacuum pump.

Trouble is, a stinking vacuum pump is just as expensive (or even more so) than a boiler. In any case it is way more expensive than the cost of a one size increase on a boiler. Further more, it is not sure that the cost for sucking the vacuum is less than the increased fuel use. This depends a lot on how tight your steam pipes are.

The enormous bonus comes from the accelerated time of arrival for the steam at your radiator. By the time the boiler is steaming, the vacuum pump has done its sucking. But that’s something else.

In your application, you could try installing a hi-lo burner and fire the high output for a little while at startup only. Get rid of the foul air from all the radiators and mains, even the distant ones. Then, keep a smaller amount of steam going everywhere while the radiators won’t fill completely anymore. This would require experimentation.

Just some happy thoughts.

Bob Sweet

I usually don't enter the relm of steam because

it's just not my thing. But when the Wall is calm I will venture into the posts to keep my mind occupied.

Christian I would'nt really know if your insights were correct or not (although my guess is, they are) but I love to watch a guy think beyond the norm, that's what the Wall to me is all about, innovation, a guy just thinking his way through something.

Can't think of a better way to spend my down time.