questioning BTUH calc

questioning BTUH calc

PostBy: mooseman100 On: Tue Mar 08, 2011 9:41 pm

I used info online from mrhvac.com. It was pretty detailed, asked about sq ft of outside wall, and roof, type of doors and window as well as thier proximty to the sun. It came out just a hair under 100,000 required. What seems odd to me is that I am heating nearly 5,000 sq ft of home with alot of tall ceilings. My trophy room alone is 1,200 sq ft with 14' tall ceilings. There are other tall ceilings in the house as well. It is a newer home with proper insulation and I live in Winchester, VA, 2 hrs south of Harrisburg, pa. Does this sound light to you guys?

I currently am heated with 2 zones of heat pump with LP back up, I think each unit is a 2 1/2 ton unit.
mooseman100
 
Stove/Furnace Model: EFM 520

Re: questioning BTUH calc

PostBy: Rob R. On: Tue Mar 08, 2011 9:48 pm

I am not surprised at the 100k btu figure. What did you use for design temperatures?
Rob R.
 
Stoker Coal Boiler: EFM DF520
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Other Heating: Dad's 1953 EFM Highboy

Re: questioning BTUH calc

PostBy: Flyer5 On: Tue Mar 08, 2011 9:51 pm

I can believe that for your climate , it sounds to be close.
Flyer5
 
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Re: questioning BTUH calc

PostBy: mooseman100 On: Tue Mar 08, 2011 10:12 pm

I used 70 degree inside and 20 degree outside. So maybe a KA-6 would do it and not the KB-8. It will be in an outside shed does that add much into the calculation?
mooseman100
 
Stove/Furnace Model: EFM 520

Re: questioning BTUH calc

PostBy: Rick 386 On: Wed Mar 09, 2011 12:06 am

mooseman100 wrote:I used 70 degree inside and 20 degree outside. So maybe a KA-6 would do it and not the KB-8. It will be in an outside shed does that add much into the calculation?



You just have to plumb it correctly to get that 100 k inside the house. How long a run, what size pipe, etc.



Rick
Rick 386
 
Stoker Coal Boiler: AA 260 heating both sides of twin farmhouse
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Re: questioning BTUH calc

PostBy: Sting On: Wed Mar 09, 2011 12:15 am

mooseman100 wrote:I used 70 degree inside and 20 degree outside.



ummmmm --- so your targeting a 50 degree temperature rise on the dwelling

because ......

It never gets colder than 20 in your back yard

I am moving there.
Sting
 
Other Heating: BurnHAM=NG-gas

Re: questioning BTUH calc

PostBy: Richard S. On: Wed Mar 09, 2011 12:51 am

mooseman100 wrote: It is a newer home with proper insulation and I live


That's a big factor , how thick are the walls? If they are 6 inch I could really believe it.
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Re: questioning BTUH calc

PostBy: Sting On: Wed Mar 09, 2011 9:13 am

http://lwf.ncdc.noaa.gov/oa/climate/onl ... ntemp.html

The mean temperature (average) for January of the last 30 years in Roanoak VA is 35.8

In Green Bay its 15.6

Now we all know it get colder than 15 in Green Bay and the same holds true in VA -- So my point is if your design temperature rise is only 50 degrees - when it the weather will turn cold and you have evenings below zero - you WILL need a second source of energy to add power to the system. An oil or propane backup or dual fuel will not fail over and help pick up the load. While I recommend under-sizing the solid fuel appliance as you have - because it will operate more of the time at its peek efficiency - you will need some sort of primary/secondary or series boiler configuration where they both can run. And they may both have to run as much as 100 hours a season, with this low a calculation.

Now that written -- if your using a negative 20 not positive 20 and calculating your design load up from 40 degrees colder -




Thats a nice house! 8-)
Sting
 
Other Heating: BurnHAM=NG-gas

Re: questioning BTUH calc

PostBy: steamup On: Wed Mar 09, 2011 9:34 am

20 btuh/sq ft is reasonable for a very well insulated newer house. However, do not cut yourself too tight with solid fuel device sizing, as they are slower to respond.

ASHRAE Weather Data indicates at the 97.5% design dry-bulb is 10 deg. f. for Winchester. This means on the average, the temperature is at or above this temperature 97.5% of the time. If you use this temperaure without a safety factor, your heating system will struggle 2.5% of the time on average.

I would re-run the calc using 10 deg. f. Make sure you have a safety factor in the calculation for pickup, piping losses and unforseen such as extreme weather conditions. For an outside shed and piping to the structure, I would add and additional 15 to 20% above this number. The shed will be toasty warm.

I would not go less than a K-6 and might consider a K-8 for that amount of sq ft. Consider the K-8 if you want to indirectly heat your Domestic water also. With that large of a house, you must have several bathrooms.

Be careful in planing the piping between the shed and house. You will need more than one single pair of 1" lines.
steamup
 
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