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Need help with Slant/Fin input

tom3holertom3holer Member Posts: 45

I am using the Slant/Fin calc to do a heat loss on my old home on Cape Cod.

I have some questions on some of the inputs.

As far as windows go: In the Kitchen we have a lot of windows. They are newer Anderson thermopane type as is the door. Once I have the square footage I am not sure as what to use for a H/L factor as the options are single, double, and triple glazed. Not sure what category these would be called.




  • icesailoricesailor Member Posts: 7,265
    edited March 2013
    Window Factors:

    Use the double pane factor for Anderson double pane windows. The single pane factor should allow the use of Storm Windows that actually give you a higher resistance factor because of the larger air space. Use the triple factor if you have Andererson types with a storm.screen sash. That makes it a triple pane window.

    The window factors get changed when you choose the type of wall construction. Whether insulated walls or not.
  • SWEISWEI Member Posts: 7,356
    accurate window factors

    are available from the manufacturer as a unit U-value which includes the sash, frame, muntins, etc.  I'd call Anderson and ask...
  • icesailoricesailor Member Posts: 7,265
    IBR And Slant/FIn Calculations:

    The Slant Fin Heat Loss Program is based on the IBR H-22 Heat Loss Guide calculations. They had two ways of doing it. The "Detailed Method" where you calculated everything including how much cat hair was between the window panes. And the "Modern Method" that was a lot easier. No matter how hard you tried, you always came out with the same heat loss. The "Modern Method" does a lot of averaging. When you pick a wall system, it is given a heat loss value. It takes the size of the exposed wall system. If the factor for a wall is .07, it means that one square foot of the wall looses .07 degrees per square foot per hour per degree per hour at 70 degrees. The window loss, once established is a constant. The program  corrects for the window types. In the scheme of things, knowing the exact rating of a window might mean 3" of baseboard, plus or minus which is usually rounded UP, not down. You can get nuts trying to add every variable in but the results will be the same.
  • SWEISWEI Member Posts: 7,356
    analysis paralysis

    is indeed possble

    Being off 10 or even 20% on window U-value or shading coefficient in a typical residence is not going to have much effect on the end result.

    Glazing on a multi-story curtain wall office building is an entirely different beast.
  • tom3holertom3holer Member Posts: 45
    That helped

    Thanks for the help. I will finish up tomorrow and compare it with the "Fuel Used" method I did today.

  • nicholas bonham-carternicholas bonham-carter Member Posts: 6,535
    Fuel used

    I would like to know more about the fuel used method, and how it compares to the slant fin heat loss. Did you take the consumption figures, and then divide by the numbers of hours in the metering period?.--NBC
  • icesailoricesailor Member Posts: 7,265
    Commercial Buildings:

    And that is a whole other subject for doing heat loss in commercial buildings.

    Not to ever be discounted except at your own peril and potentially bad results.
  • tom3holertom3holer Member Posts: 45
    edited March 2013
    Fuel Used

    On another forum I was given detailed info on using the fuel used method.

    It involves using HDD or heating degree days, design outside temp, and of course the Therms used and the number of days of the billing period. I also subtracted the summer average of therms used as the heat was off and these were the drier,cooktop and hot water usage. This gave me a more accurate usage of the gas being used just for heat. It would seem this is a very accurate method because there is no guesswork as to insulation, air leakage, etc. I ran it for 3 months and the numbers were very consistent.

    I am soooo sorry I did not take the time to do my DD and educate myself on hydronics and heatloss. I live in an home built in 1860 of 2300 sq/ft. It has upgraded windows and some blown in wall insulation.

    The old boiler was a W/M VHE3 installed 22 years ago that went through igniters once a year. It always was short cycling, on for a very short time, off, then on again. I was told by the installer that that is how they are designed to work. BS

    I contacted 3 plumbers/contractors to see about getting a new system. It seemed the new ModCon boilers were far more efficient and would work better in the long run. They all were on the same page as to the size I needed. Basically it was "look at the old boiler and get one at least that size or slightly bigger" BAD IDEA. Not one of them even offered to do a rough heatloss and God forbid a real Manual J on the house. I wound up with a Alpine 150 with a new Superstor 45gal  indirect water heater. I won't bore you all with details but my installed did not have a clue how to size or setup a modern Modcon boiler.

    First cold day, around +10 deg we could not keep the kitchen warm. It was loosing ground going from 70 down to 67 lower. He actually wanted to install a coil/fan type of additional heat under the cabinets. I told him that we never had a problem with the other boiler and it was slightly smaller than the new one.

    This is when I began to do my own research and began to understand what was going on. Boiler is way too big for my home basically.

    The slant/fin heatloss came in at around 69k. Again this is not all that accurate as the kitchen which has a lot of glass is all Anderson thermopane type but the program does not show this type as an option so I used double glazed.

    Now the "NEW" contractor I had contacted to look the system over  and do a Manual J said that with these older homes the manual J is not that accurate and suggested to do a abbreviated one. He sent me the results and it came in at 92k. Not sure what he was using but this does not even come close to my figures.

    I have figured it two completely different ways, over 3 months and this is what I got.

    Using the slant/fin pgm     69K

    Using the "Fuel Used"      55K

    The fuel used although there are some errors involved should be the most accurate.


    Because I did not do my research I have a rather inefficient heating system compaired to what it could have been.

    Yes, I have tweaked the boiler quite a bit after reading all I could find and it is running much better although not a well as if it had been the proper size for this house.

    I will ask the gentleman that gave me the way to work the "fuel Used" method if I may post his method here.

  • JeffGuyJeffGuy Member Posts: 70

    I don't understand how a boiler "way too big for my home" would cause "first cold day, around +10 deg we could not keep the kitchen warm."

    You may have a loss of efficiency with too large a boiler, but how could it fail to keep your house warm? That would seem to point to a problem with piping setup, or with the control adjustments. Has that been corrected?
  • icesailoricesailor Member Posts: 7,265
    I agree:

    I agree with JeffGuy. Your conclusions are erroneous. The opposite would be true if the kitchen wasn't warm.

    The installer must have changed something that caused your problems.

    The one thing about over-sized systems, is that you will not have DHW supply problems.

    And the hole in your supposition is that the only time a properly sized boiler is properly sized, is on the few says per year that it is correct. The rest of the time, it is WAY OVER SIZED.

    The vehicle you drive around in is grossly overpowered. Until you are trying to get on to a limited access highway and someone won't let you into traffic.
  • tom3holertom3holer Member Posts: 45
    edited March 2013
    Let me explain

    Let me explain why my oversize boiler was not able to keep the kitchen warm. Its not as simple as one might think at first glance. A modern modcon that is way oversized when called for will come on, fire up to the set temp, then try and keep that temp till the call for heat is no longer there. The problem with an oversize boiler is that if it cannot keep the heat within temp limits it shutsdown due to overtemp. This was my case. It came on, ran up to temp, but even on the min mod was unable to keep the temp within the set limits so it shutdown. Now the startup time is about 2 minutes. Add to that the time it takes to come back up to temp so now the average water temp is quite low. That is why the kitchen never could get up to temp on that cold day. I was able to help the problem by raising the overtemp limit to its max and combining two zones into one. This helped unload the boiler and kept the short cycling down. When a system is short cycling due to way excess btu output this is only one of the problems. 

    My plumber did not necessarily plumb anything wrong he just didn't understand how these systems work and never took the time to set it up properly along with way oversizing the boiler.

    " The one thing about over-sized systems, is that you will not have DHW supply problems.

    And the hole in your supposition is that the only time a properly sized boiler is properly sized, is on the few says per year that it is correct. The rest of the time, it is WAY OVER SIZED."

    I am not a hydronic engineer but have spent quite a bit of time delving into my installation and reading all I could about this type of heating system. Actually I just retired as a pilot for Delta Airlines after 35 years so it has given me something to do.

    I have an oversize boiler and have a terrible DHW problem to boot. New Superstor installation by the same plumber and lack of hot water during a shower. Problem is the Tstat that comes with the Suporstor has a wide temp range from call to off. This translate into the water getting too cool before the call for heat is there again so it gets behind and its hard to catch up even with a lagre boiler. One fix is to replace the tstat with one that has a variable delta t and lower it to a few degrees.

    If a boiler is sized to the BTU's needed on the coldest day and it is of the Modulating type then no it is not way oversized  the rest of the time as it will be able to modulate down to what is needed especially if an OAT reset in used.  

    I hope I have clarified my earlier post. It does seem backwards that a larger boiler couldn keep up, but when you understand what was going on it makes sense.


    Cape Cod
  • icesailoricesailor Member Posts: 7,265
    Wrong Conclusion:

    Everything I know about aircraft, I can relate to heating. And so forth..

    If you have ODR, the water temperature can be made to go down. Even if you don't, you can still make it go down.

    As far as aircraft, old Helicopters had Recip engines. More than 60% of engine power went to counter-rotate the fan with the tail rotor. They were limited in what they could do by the HP of a recip. The development of gas turbines and their excessive HP made it so that you could get better performance with the excess HO. The tail rotor needs didn't go up significantly, but that excess HP could be used by the fan. The Kaman design of twin counter rotating fans eliminated the need for the excess power. The turbines  made the Kaman obsolete.

    Your excess nuts in boiler HP isn't causing your problem. Its excessive high heat and short burns. If the thermostat is calling, the circulator shouldn't stop running. If it does, you have another issue.
  • icesailoricesailor Member Posts: 7,265
    Or put another way:

    Or put another way,

    You may see it that way. I've never seen that way to be true. I've never seen it to be true for me or anyone else, but it mght be true for you.

    I guess all those houses that were uninsulated and had heating systems that worked, had the envelope tightened up and insulated with new windows.

    Thinking about all the boilers I never saw stop working, just stuns me.

    Its a good thing that they don't put them in like that anymore.
  • tom3holertom3holer Member Posts: 45
    edited March 2013
    Or put another way


    The circulator does not shut down when the zone is calling for heat. The boiler does/did once it hit the overtemp limit. The overtemp limit was factory set at 2deg above the setpoint. So its easy to see why it was always shutting down. It wasn't the actual water temp, it was the overtemp limit which is a set value above whatever the setpoint temp is at that time. I raised the overtemp limit to 10deg and it  helped with the short cycling.

     I am confused by your statemen: "Your excess nuts in boiler HP isn't causing your problem. Its excessive high heat and short burns"

    I agree that its the short burns but that is a direct function of having a boiler too large that cannot modulate down low enough to satisfy a zone without overtemping.  

    Or put another way: Its like haveing an engine on a plane that will not throttle down low enough for cruise flight. Its great for takeoff and climb, but once you level off the plane will exceed redline speed so you have to shut the engine off till the speed gets down and then start it up again and so on and so on , not very efficient.

  • icesailoricesailor Member Posts: 7,265

    "NUTS" equal Horse Power.

    When you hit the power switch and start the engine(s) in the airplane, the engine runs until you turn it off. When you need power, you open the throttle and give it more gas to get more "Nuts" out of the motor. Consider the motor the circulator. It is always running to effect the load. You can keep the prop in the green power range but you don't always need power to do it. When you are climbing, you need more power. The hotter water in the system is the power. When you level off, you don't need the same power. You can keep the RPM's the same, but you don't use as much fuel. Close off the air and the EGT goes up but RPM's might go down. So, you adjust.

    Your Mod Con does this autiomatically by changing the water temperature. Instead of a throttle, it has a high limit switch. If the power requirements need less power, but the settings don't change, you get overspeed. Bigger bite (higher load) lower RPM's.

    When the OAT goes down, the load on a heating system goes up. You need more energy. When the OAT goes up, you need less energy.

    Some here that aren't in the know, seem to loose it when they hear their burner stop and start. Ignore it. When you are driving your car down the highway, even if you put the throttle on cruise control, the throttle is going up and down all the time. That's normal.

    Recip engines are limited in that their maxmum HP is at the top of their power band. Turbines don't have that problem. They have huge amounts of escess power throughout their power band.

    Here's another example. Gas hot air baloons. They are always hitting the gas valve to keep it up The circulator is like the engine. It delivers the power. The engine (burner) keeps the power available.

    I have 5 zones of FWH heat in my 2,700+ house. If only one zone is calling, the burner cycles constantly. But if all zones are calling, and it is cold out, it may run for hours without stopping.

    If your circulator is coming on and off all the time, that's another issue. If the circulator keeps running and the burner is cycling, it's normal.
  • tom3holertom3holer Member Posts: 45
    Different ways of looking at it


    We, obviously, have different ways of looking at the problem. Thats fine. You have, I gather, many many years of experience in this business, I do not. I respect your opinion and do thank you for the input and suggestions you have made.

    I am learning this is a rather complex business but  became disappointed by the effort, or lack thereof, by several installers when it came to proper sizing and setup of a new system to optimize efficiency.

    I do have many more questions and will post here later and, if you will,  look forward to your suggestions and advice.

    Wife is giving me the look as I told her I'd walk the dog 2 hours ago.


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