Can we gain worthwhile efficiency with new steam boiler?

Bioman

Greetings,

I am an energy auditor looking in to a STEAM boiler replacement for a customer with a large victorian house in Minnesota. They currently have single pipe steam radiators, so we need to stay with steam. They have a natural gas Weil-McLain model H-8, series 4 steam boiler mfg'd in the early 1960's (per Weil McLain). Kbtu In= 490, Kbtu Out= 392, thus the thermal efficiency was already 80% at date of manufacture. I have looked thru website from AHRI, and cannot find anything in steam better than 81% Thermal eff now. Am I missing something? Why bother, except for reliability/ parts issues, right? How about adding a good quality flue damper, and call it good? Or do this with a new steam boiler?



Home envelope/ air leakage measures are being addressed to save energy. I just do not want to overstate savings for a boiler replacement here.



We know that hot WATER is a different animal (way more common) and these can save a lot of energy and $ to replace. I would appreciate a second learned opinion...

Thanks!

Bioman

j a_2

greening of steam

Get Dans book The Greening Of Steam….Easy read and lots to learn….j.a

JStar

Steam

We install A LOT of steam boilers, and always achieve higher than 83%, often as high as 88% efficiency. We use a wet base boiler and gas burner. This is not yet listed with AHRI, something I'm working on currently. Hopefully, soon, it will be tested and listed so it can be used in energy audit proposals. A steam SYSTEM is the most efficient SYSTEM available, despite always receiving the lowest AFUE ratings.



With proper near boiler piping, upgraded venting, and low pressure controls, we have saved customers as much as 60% on their fuel bill.

nicholas bonham-carter

Checking steam for efficiency

A steam boiler operating at peak efficiency will have been sized according to the EDR of the total radiation of the house, and set to a few ounces of pressure, with generous main (not rad) venting the supply piping will have been insulated, and checked for proper slope.

Addressing all the envelope insulation/infiltration issues is important as well.

If after measuring the radiators, you find the boiler to have been over-sized, then that is a source of inefficiency through short-cycling.

The use of short temperature setbacks can waste energy as well. A constant 65 degrees, can be more comfortable then alternating between 60, and 70 degrees. When you are comparing the cost of heating between steam and hot-water, don't forget to take into account the electricity consumption of the pumps.--NBC

vaporvac

Stage-firing

You can also add to the efficiency by stage-firing two equal sized wet-based boilers or using a burner with some sort of modulation to achieve the same thing, or both. That way the burner cuts back after steaming is achieved.

tThe wet-based boilers with a gas conversion burner ran about the same in my case as a homeowner, so it was a question of efficiency and longevity. Many professionals on this site do this type of install, as well.

Jamie Hall

Efficiency...

The published AHRI efficiency figures are a little like the miles per gallon figures on a car's sticker, only worse: your mileage may vary.  More to the point, steam boilers are not properly measured, or at least not measured in the same way, as hot water boilers are; you simply can't compare the two sets of figures at all.



A good, modern steam boiler, matched to the system its driving and properly fired and adjusted, can easily reach into the mid to high 80s on efficiency (the boiler I care for runs  around 86%)..



As has been said, though, steam is rather sensitive to details (although once you get it right, it will stay right with minimum maintenance).  Insulating all steam mains.  Proper venting.  Proper slopes on pipes.  Setting the operating pressure correctly.  Getting the near boiler piping right (don't cut corners here!).  Keeping the setbacks small, if at all.



Making sure the burner is properly adjusted.



I myself am not keen on flue dampers, although they may increase the overall efficiency a little bit (not measurable conventionally, though) as they are, IMHO, a nuisance and maintenance bother.  A barometric stack damper may be needed, though; you will find that out when you adjust the burner.

John Mills_5

Different efficiency numbers

Remember that modern boilers talk ANNUAL efficiency so they are saying that over the course of cycling all winter, they are delivering 80% or more of the heat into the home.



If a tech reads combustion efficiency or a boiler says its output is 80% of input, that doesn't always mean the same as the annual number or AFUE.



The old boiler may not burn efficiently, heat pours up the flue 24/7 while the modern boiler has a damper. The sections on a modern boiler are designed for maximum heat transfer. The higher AFUEs come from wet base boilers like Jstar mentioned so the water surrounds the fire not just above it. The inside of the sections could be limed up providing insulation from the heat wasting fuel.



If you could know the annual efficiency of a 50 year old boiler (you really don't want to) you could find it 50-60%.

Kevin_in_Denver_2

To Sum Up

"With proper near boiler piping, upgraded venting, and low pressure

controls, we have saved customers as much as 60% on their fuel bill."  I'll add - putting the correct thermostat in the correct location.



These savings can be achieved even without a new boiler, and these system corrections usually achieve better payback than boiler replacement.



Some other more obvious points:



1.  A very thorough inspection of the existing boiler can enlighten you about the need for replacement.  So the boiler replacement could be far down the priority list if the budget is limited and the boiler is in good shape.



2.  If you perform the home envelope improvements at the same time as the heating system improvements, it will be impossible to know how much energy was saved by either one. You will have blown a chance to learn a lot.



3.  If the boiler room has it's own combustion air supply, then the savings gained by a vent damper are minimal.  If you tighten the house, you have to have a fresh air inlet for the boiler room.  Then you should also tighten the boiler room door.  Make sure that  -15F air coming in the fresh air supply duct won't freeze a pipe.



A word about setbacks and occupant comfort --

Assuming the occupants shower in the morning:

The best way to guarantee that the radiators are hot (and radiating) in the morning is to set back the thermostat at night, and back up well before the alarm goes off.  IMHO, the warming effect of a hot radiator outweighs all the negatives about setbacks.

BJN420

Outside the box

Ever think of getting a self feeding coal boiler?

I'm getting one to install in my home, I feel low gas prices will lure everyone into a false sense of economic security then ,BAM! Coal has been stable for a while and it's easier to tend