Heat loss calc - sound about right?

[offroadaudio]

I'm starting at ground zero here in order to build the right system for my needs / budget.
Just looking for a simple confirmation on the heat loss calculation that I just did:

I got 210 M BTU/year or 102,000 BTU/hr.

I know there are a million variables, but do those numbers sound like they are reasonable?
Just want to make sure I didn't screw something up at this point.

Thanks.

 

[bpirger]

Could you say a little something about your load, ie what are you trying to heat? 100K BTU/HR is a good size load, perhaps a very large house, or a medium house poorly insulated, or an inground pool chanigng by a degree or more......

For my 2500 Sq ft house with R19/R38 insulation, I calculated right around 40K/HR, at 0 outside.

So without knowing what you are doing.....I'd guesstimate you are within a factor of 2. Not off by 10!

 

[Tennman]

Ah... if you're just trying to convert your annual energy consumption to an hourly rate.... 365 days x 24 = 8760 hrs/yr.
210M btu/yr divided by 8,760 hrs/yr = 23,972 btus/hr.... but I'll bet you don't burn for 365 days a year. If you assumed you burned for about 86 days/year then your conversion is right. Folks here are going to ask about how big your house is, if it's reasonably well insulated, and probably where you live to give you a sanity check on your heat loss calcs. 102k btu/hr could be a very small house way north or a very big house near me. Pretty good chance there's someone here with a house similar to yours in size and latitude.

 

[offroadaudio]

Could you say a little something about your load, ie what are you trying to heat? 100K BTU/HR is a good size load, perhaps a very large house, or a medium house poorly insulated, or an inground pool chanigng by a degree or more......

For my 2500 Sq ft house with R19/R38 insulation, I calculated right around 40K/HR, at 0 outside.

So without knowing what you are doing.....I'd guesstimate you are within a factor of 2. Not off by 10!

Thanks - that's kinda what I was looking for - if "5" was more typical and I got "5,000,000" I would re-check things.

The house is about 2900sq. feet - it's a post & beam construction with the insulation on the outside. The insulation is rigid foam, but not the nice blue or pink stuff - I think it's an older style and just "Styrofoam". It makes the envelope tight, but the r value isn't great - I'm guessing about R7 for 2 inches.

The ultimate goal is staple-up radiant for the first floor, with the same boiler making the hot water for baseboards or radiators in 2 2nd floor bedrooms.

I'm thinking now that a per room heat loss might be the better way to start things off?

Thanks for the help.

 

[rkusek]

You didn't mention your home size, age, location, or other details. The number is definitely in ball park however. My ranch home build in 2008-09 is conventional construction with 2x6 R19 walls, R49(R19 fiberglass+blown in on op) in ceiling and 2200 sq. ft main floor near Omaha, NE. Decent amount of windows all Pella double pane with the 3rd pane with the integrated blinds(not as good as triple pane though). The Slant Fin software I used came up with 35k btu for main floor and about 30k btu for the unfinished but insulated basement on a 10* design day. I'm still running my EKO 40 without storage and decent to marginal wood(some wetter & some not the best quality). My homemade barn heater where boiler is located cicrulatges 24/7 and pulls about 10btu when water is hot. My load for everything on 10 degree day should be about 75k btu/hr based on this. EKO 40 is rated at 135k ideal but most people here would say its more like 100k with average wood and operation. In addition, I only run the combustion fan at 50% to burn slower since I don't have storage. It runs about 7 hrs compared to about 4 hrs at 100% under full load. When I run the fan coil on the homemade barn heater (and barn is cool) and house also drawing load, the EKO won't go into idle and will burn a load of wood in 4 hrs. Based on all my unscientific observations, I think the Slant Fin numbers are probably off by 10-15k btus and should be more 50k btus. You might want to try a couple different heat loss programs to see how much they vary.

UPDATE: now I see your numbers...the load calculated is probably close based on that R value.

 

[offroadaudio]

You didn't mention your home size, age, location, or other details. The number is definitely in ball park however. My ranch home build in 2008-09 is conventional construction with 2x6 R19 walls, R49(R19 fiberglass+blown in on op) in ceiling and 2200 sq. ft main floor near Omaha, NE. Decent amount of windows all Pella double pane with the 3rd pane with the integrated blinds(not as good as triple pane though). The Slant Fin software I used came up with 35k btu for main floor and about 30k btu for the unfinished but insulated basement on a 10* design day. I'm still running my EKO 40 without storage and decent to marginal wood(some wetter & some not the best quality). My homemade barn heater where boiler is located cicrulatges 24/7 and pulls about 10btu when water is hot. My load for everything on 10 degree day should be about 75k btu/hr based on this. EKO 40 is rated at 135k ideal but most people here would say its more like 100k with average wood and operation. In addition, I only run the combustion fan at 50% to burn slower since I don't have storage. It runs about 7 hrs compared to about 4 hrs at 100% under full load. When I run the fan coil on the homemade barn heater (and barn is cool) and house also drawing load, the EKO won't go into idle and will burn a load of wood in 4 hrs. Based on all my unscientific observations, I think the Slant Fin numbers are probably off by 10-15k btus and should be more 50k btus. You might want to try a couple different heat loss programs to see how much they vary.

UPDATE: now I see your numbers...the load calculated is probably close based on that R value.

I think that's a good idea - will try a few others and take an average.

 

[WhitePine]

You don't say what you used to calculate the heat loss. In case you find it handy, here's a link to the best free heat gain/loss calculator around, courtesy of the taxpayers.

http://www.energy-design-tools.aud.ucla.edu/heed/

The instructions explain how to use it for any state.

 

[offroadaudio]

I used one I found on google - solarheat.org maybe?
Will try this one too.
Thanks

 

[Tennman]

So for my education, offroad, where did the 210M btu/yr come from? Did your load calc program compute energy load by the year?

 

[offroadaudio]

Yes, that was one of many figures it gave. After providing area of outside walls, floors, ceilings, window area etc... - it then gave that calc based on the volume of the home. I'm not sure yet just how useful that figure is.

 

[Willman]

Where your going hydronic a room by room HL is a good way to go. You will need each rooms HL to figure amount of emitters and loop length. It should be close to whole house HL. Not exact due to closets and hallways etc.If you can get an accurate read on your insulation in the walls that would help. A HL analyisis is only as good as the info that is put in.

Will

 

[stee6043]

Holy smokes you guys are talking some huge loads. At 100k per hour average you're going to be in the 15+ cord per year range if I had to guess. I have a 2x6 constructed, 3,200 square feet, 2003 built home. My average heat load in winter is between 20k-30k btu/hr. My peak load when temps dip below zero at night and barely break 10 during the day is closer to 50,000 but per hour. I'm considering adding more instulation in the attic to improve my situation next year.

I think you'll have to have a pretty unique staple up system to handle this kind of load. You'd be looking at 34+ btu/hr/sq.ft. Big pex, close loops, high dollar plates may be your only shot at getting these kinds of numbers?? I believe the average in-floor system pushes 15-25 btu/sq.ft.

Let me be the first, and not the last, to say that your money right now would be much, much better spent on insualtion and reducing your heat load. This should be your ground zero...

 

[offroadaudio]

Holy smokes you guys are talking some huge loads. At 100k per hour average you're going to be in the 15+ cord per year range if I had to guess. I have a 2x6 constructed, 3,200 square feet, 2003 built home. My average heat load in winter is between 20k-30k btu/hr. My peak load when temps dip below zero at night and barely break 10 during the day is closer to 50,000 but per hour. I'm considering adding more instulation in the attic to improve my situation next year.

I think you'll have to have a pretty unique staple up system to handle this kind of load. You'd be looking at 34+ btu/hr/sq.ft. Big pex, close loops, high dollar plates may be your only shot at getting these kinds of numbers?? I believe the average in-floor system pushes 15-25 btu/sq.ft.

Let me be the first, and not the last, to say that your money right now would be much, much better spent on insualtion and reducing your heat load. This should be your ground zero...

I'm sure you're right, and I do plan on adding insulation. My initial numbers are not really correct however, because the radiant is only going to be utilized in one large part of the house. So, using the whole house numbers doesn't make sense. I'm going to re-run just the area that I plan on using the radiant under - plus 2 radiators in bedrooms above. Currently I heat the entire house with just my wood insert, but it gets real difficult when temps get under 20. I'll continue to use the insert, but want the floor at least warm to greatly improve comfort - so the radiant will not need to handle the entire heat loss. Thanks for all the thoughts. I just ordered a $150 book on radiant design that is reported to be the "bible" of hydronic heating - I'm sure it will spur as many questions as answers - but eventually I will start to build this thing when I have a certain comfort level that it will work well.

I'll post some drawings of incomplete system ideas soon and hope to get some input with those. Thanks again.

 

[Como]

That calculation would produce a simplistic number of 35 btu sq ft max, at your lowest designed temperature using whatever you chose as your high temperature.

Rule of thumb would be that your actual normal would be half that so within the realms of in floor radiant.

I did my calculations using a variety of different web sources treating the building as a single room. When the pro did his Manual J he came back with a number that was 25% less than my highest number, about 5% less than my lowest number.

I am really hoping his number is right in practice! The Manual J is really just a best guess, so many variables.

I specified mine with a low of -20, it is very rare for us to get down to that or lower for more than a day or so at a time and then several times in a year. We have hit -40 but that was only for a night and I can not justify a system on the basis of a single night every x years.

There is also the flywheel effect if you have a lot of mass in the building, takes longer to heat up but longer to cool down.

So hopefully in practice his peak 102,000 will be nearer 80,000, his usual load will be nearer 40,000 the annual multiplier seems in the area for me. Sun makes a big difference for us, the next 4 or 5 days will be in the 40's and sunny, I doubt if the heating will come on, as soon as the sun goes down it changes! Not something the calcs take much account of.

Wood usage, well it could be 10 cords of decent hardwood, probably a bit less.

 

[WhitePine]

There is also the flywheel effect if you have a lot of mass in the building, takes longer to heat up but longer to cool down.

I don't think I have ever heard it termed flywheel effect before, but it is certainly an apt description. I love it. We have a huge amount of designed-in thermal mass in our house, and it does exactly what you say. It really helps to stabilize the temperature inside, both winter and summer.