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Adding attic & wall insulation effect on steam boiler?

We're thinking about adding some attic & exterior wall blown in dense pack or other insulation to our building depending on what our energy auditor and insulation company recommends.  With some energy rebates offsetting the cost a bit, any guesses on how long a payback in years we might see? 

We currently have about 6-12 inches of attic space & 5-6 inches of empty wall space behind the exterior brick walls in our  5 unit, 2 story Milwaukee, WI building. We have a WMC EG 75 single pipe steam boiler system.  

We're wondering how this will change the boiler run time after insulating, and what % of fuel savings we might expect if anyone has any experience with before & after comparisons or anything else we should be thinking about?

Comments

  • mattmia2
    mattmia2 Member Posts: 5,738
    there are calculations you can do with before and after heat loss and heating degree days to predict the potential savings
  • Jamie Hall
    Jamie Hall Member Posts: 19,150
    Depending on the before vs. after heat loss of the building, the boiler total run time will be reduced accordingly. You can make a ball park estimate by running a heat loss calculation on the existing condition and then another on the new condition. This will be no better than a ballpark, however, as the overall impact of insulation and infiltration fixes is nowhere near linear, and while it will be a guide for more extreme conditions, it will be at best a good guess for warmer outdoor conditions.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • The other item that needs to be taken into account is where the boiler will be operating on its efficiency curve. The lower the load versus the boiler rating, the lower the efficiency on an on/off boiler. Once an atmospheric boiler is operating below about 30% load the efficiency drops off very rapidly. With steam radiators so oversized and the boilers usually oversized to the radiators, you can get into that less than 30% load for nearly the whole heating season very easily. All this is why we orifice most 2 pipe steam systems we work with.... we can downsize the radiation and boiler ( or downfire a power burner) to the correct load according to heat loss and reduce fuel consumption because the boiler operates much higher on it efficiency curve. An outdoor reset control running a mod burner is the sweetest set up for these orificed 2 pipe systems.
    With your atmospheric boiler, I would install a stack damper to help reduce the standby losses of the boiler when it is operating at such low loads.

    The other thing that also needs to be taken into account is that insulation/ air tightening typically shortens the heating season .... the amount of days the boiler even needs to run. Internal gains and if you are lucky, good solar gains, will be able to heat the house down to lower temperatures, reducing the need for any heating at all. Most older building need heat at around 65F average outdoor temperature, which for here in Chicago give you a heating season of about 6127 degree days. If insulation and air tightening can reduce that heating season start temperature down to 60F, then the degree days drop to 4940 in Chicago, a 20% drop in heating needs.

    An example, we kept our Church facility at 45 to 50F all last winter because no one was meeting in the building. That reduced the degree days to around 1200. In addition, at that low interior temperature, the ground begins to provide effective heating of the building. We ended up using about $1200.00 of gas for the winter to heat a 17,000 sq ft structure. We also using a new staged fired steam heating plant for most of the heat supplied.
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    wlgann
  • wlgann
    wlgann Member Posts: 14
    How are you doing blown-in wall insulation on what sounds like a brick building? You don't often see that. I have doubts that wall insulation will get you a good ROI because a masonry structure will tend to have very little air infiltration as compared to a wood framed building. You might make it a bit more comfortable for the inhabitants but I'm not sure wall insulation save enough fuel to get the money back in a reasonable time.

    What's the temperature like in the basement? Is the boiler in a (well ventilated!) room or is the basement all open space? I'm thinking if the ambient temperature around the boiler tends to the 70s vs. the 50s you can get 5% fuel savings just by ensuring the water in the boiler never gets as cool. Hoping your insulation contractor recommends sill insulation in the basement.

    Also hoping your insulation contractor recommends careful review around plumbing stacks and top plates on your 2nd floor interior walls. Older buildings commonly have "hidden chimneys" around these features where heated air can escape the building.
    NYtimebombPC7060
  • cubicacres
    cubicacres Member Posts: 355
    Thanks-we were wondering about the boiler becoming over-sized after attic & wall insulation is installed and not needing to run as often or as long. We measured all the mains, risers, pipes, radiators & saw around a 33% pickup factor for the current boiler when installed in fall 2015. We have a Tekmar 279 with 1 outdoor & indoor sensor for the 5 unit building, so hopefully it can learn it doesn't need to run as much after being insulated to save some fuel. Ideally we might have done the insulation before getting the new boiler a few years back... :/

    Our energy auditor saw 5-6" of space in the walls from the basement looking up near the risers, so thought that would allow some type of insulation gains, along with attic insulation. The basement is cooler, and has a crawl space with 5 feet of dirt in one corner, so he advised a vapor barrier & insulation layer to keep that seperated from the other rooms & keep out the moisture. We'll see what his report says & get some estimates from the insulation companies.

    The boiler room is seperate from the rest of the basement, but has some air gaps/space to the next room & is around 70-74F this year. We do see 3-4 abandoned chimneys in the rooms & outside from the roof (the old "plates" on the walls near the ceiling) that may have had old wood stoves in each unit.

    Do you think using the Tekamar, we should watch it after the insulation & try reducing the boiler % down from 100%, or adjust the outside WWSD temp. or other settings for better run time/fuel savings? Hopefully it doesn't become so efficient that it has moisture build-up/rust from shorter-cycles, unbalanced/oversized heat supplied to rooms, etc. we can't adjust for & capture some energy savings after the insulation install.



  • Jamie Hall
    Jamie Hall Member Posts: 19,150
    Misunderstanding there. A steam system boiler is sized based on the amount of radiation which it is powering, not on the heat loss of the structure.

    Therefore, the amount of insulation or whatever in the house is quite irrelevant.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    ethicalpaulwlgann
  • You will probably need to adjust both setting. The warm weather shut down will probably need to drop several degrees since the building will be self heating for more of the heating season and the amount of time the boiler needs to run will drop, so the 100 on temperature will be much lower than it is now. I've seen lightly insulated multi-unit buildings use a warm weather shutdown of about 55F. The % on time depends on how oversized the steam system is.
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  • cubicacres
    cubicacres Member Posts: 355
    Thanks for the information :) We're thinking it can't hurt to insulate, even if it means adjusting some boiler settings. After insulating, should we use the indoor thermostat on the Tekmar as our guide for tenant comfort targeting & asking them how it feels, while lowering the boiler % & WWSD until we get it right? We've been pretty good with happy tenants at around 68F +/-1 degree on the indoor sensor & WWSD in the mid-high 50s so far.

    Our energy auditor claims typical payback periods are around 4-5 years for most reccomended projects after taking into account the Focus on Energy WI utility-funded rebates covering around 20-30% of the project costs.
  • I think the indoor sensor adjusts the boiler firing, so it may be hard to use that. My method is to eliminate the indoor sensor when it is warmer out and set the outdoor shutdown pretty low and then bring it up gradually until proper heating is achieved. Then wait for typical winter weather, disconnect the indoor sensor and set the boiler at very low duty cycle and then gradually bring it up until comfort is achieved. This should get you tuned it pretty tight, then reconnect the indoor sensor.
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  • wlgann
    wlgann Member Posts: 14

    Our energy auditor saw 5-6" of space in the walls from the basement looking up near the risers, so thought that would allow some type of insulation gains, along with attic insulation. The basement is cooler, and has a crawl space with 5 feet of dirt in one corner, so he advised a vapor barrier & insulation layer to keep that separated from the other rooms & keep out the moisture. We'll see what his report says & get some estimates from the insulation companies.

    The boiler room is separate from the rest of the basement, but has some air gaps/space to the next room & is around 70-74F this year. We do see 3-4 abandoned chimneys in the rooms & outside from the roof (the old "plates" on the walls near the ceiling) that may have had old wood stoves in each unit.

    Do you think using the Tekamar, we should watch it after the insulation & try reducing the boiler % down from 100%, or adjust the outside WWSD temp. or other settings for better run time/fuel savings? Hopefully it doesn't become so efficient that it has moisture build-up/rust from shorter-cycles, unbalanced/oversized heat supplied to rooms, etc. we can't adjust for & capture some energy savings after the insulation install.

    I don't know much about multi-unit buildings but I can say I've insulated the heck out of my own home over the last 20 years and the boiler doesn't care. It just runs less often--I set my thermostat back from 68 to 63 overnight and it NEVER fires overnight unless the outside temperature goes below 30 by midnight and stays there. Likewise during the day, and I'm fine with that.

    Sounds like you're getting pretty good advice from a competent energy pro. I have done similar things in regards to unheatable basement spaces like my root cellar and the old coal room--they have doors for access but I've pretty well sealed them off with waterproof hard foam insulation to prevent heated air getting in there and condensing. Regardless of the energy ROI on that, you probably want to do it so that moisture doesn't collect in the cold room and rot any wood or iron or terra cotta that might be holding your building up.

    You're saying there are masonry chimneys enclosed within the walls? Or just space for maybe double-walled ducts that might have snaked up through the building? You don't want to completely seal a masonry chimney; it's going to be slightly porous and needs to breathe. But you can seal it at the bottom with more masonry (use mortar with the same hardness as the original!) or with hard foam/spray foam so that heated air doesn't get into it. At the top you'd put a "hat" on it to keep rain out. It won't cause a lot of heat loss unless air can infiltrate through it.
  • PC7060
    PC7060 Member Posts: 739
    edited December 2021
    Misunderstanding there. A steam system boiler is sized based on the amount of radiation which it is powering, not on the heat loss of the structure. Therefore, the amount of insulation or whatever in the house is quite irrelevant.
    @Jamie Hall - Wouldn’t the EDR of the radiator establish the high limit of the boiler? Seem like a boiler rated at less than radiator maximum would be fine as long as it met the design day BTU requirements of the home.  

    Thanks in advance. 
  • pecmsg
    pecmsg Member Posts: 2,954
    The EDR doesn’t change with added insulation. The heat loss does go down!
  • Jamie Hall
    Jamie Hall Member Posts: 19,150
    PC7060 said:



    Misunderstanding there. A steam system boiler is sized based on the amount of radiation which it is powering, not on the heat loss of the structure.

    Therefore, the amount of insulation or whatever in the house is quite irrelevant.

    @Jamie Hall - Wouldn’t the EDR of the radiator establish the high limit of the boiler? Seem like a boiler rated at than radiator maximum would be fine as long as it met the BTU requirements of the home.  

    Thanks in advance. 


    Steam doesn't really work that way. The boiler needs to have very nearly exactly the same power output as the power input requirement of the radiators to which it is attached. Both of which are measured, somewhat oddly, in square feet (which makes sense, since the power requirement of the radiators is determined by their effective area times the power requirement per square foot -- 240 BTUh). If the boiler is significantly overpowered, that can be accommodated -- at some cost in efficiency -- by turning it off or cycling it. if the boiler is underpowered, however -- I presume, by the way, that you meant boiler rated at less than radiator... up there) there will not be sufficient steam to reach all the radiators, never mind bring them up to full output. In severe cases, there may not even be sufficient steam to heat all the piping, never mind the radiators.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    PC7060
  • cubicacres
    cubicacres Member Posts: 355
    Now that you mention it, we also have a coal room with no door next to the boiler room just across from the crawl space room filled with 5 feet of clay/dirt & seems to have a moist floor in the summertime. Maybe the energy auditor's report will suggest sealing that are up as well. We don't use that coal room, but it might be nice to store something there if we added a door if this would be more energy efficient.

    The chimney are in most of the apartment kitchen areas on the outside walls with a few feet of bump-out & have the "pie-plate" coverings a few feet below the ceilings. Maybe the auditor's report will suggest filling them with insulation or air sealing as well.
  • jumper
    jumper Member Posts: 1,866
    Maybe the steam goes to coldest radiator and when it warms up then goes to what was second coldest......?? When big boilers were replaced by multiple little ones; a strategy was to fire only one during day when nobody was home and also during wee hours when tenants slept.

    PC7060 said:



    Misunderstanding there. A steam system boiler is sized based on the amount of radiation which it is powering, not on the heat loss of the structure.

    Therefore, the amount of insulation or whatever in the house is quite irrelevant.

    @Jamie Hall - Wouldn’t the EDR of the radiator establish the high limit of the boiler? Seem like a boiler rated at than radiator maximum would be fine as long as it met the BTU requirements of the home.  

    Thanks in advance. 
    Steam doesn't really work that way. The boiler needs to have very nearly exactly the same power output as the power input requirement of the radiators to which it is attached. Both of which are measured, somewhat oddly, in square feet (which makes sense, since the power requirement of the radiators is determined by their effective area times the power requirement per square foot -- 240 BTUh). If the boiler is significantly overpowered, that can be accommodated -- at some cost in efficiency -- by turning it off or cycling it. if the boiler is underpowered, however -- I presume, by the way, that you meant boiler rated at less than radiator... up there) there will not be sufficient steam to reach all the radiators, never mind bring them up to full output. In severe cases, there may not even be sufficient steam to heat all the piping, never mind the radiators.