Heat Loss Calculation Question Uponor/SlantFin

[Sawyer]

I am calculating heat loss using Uponor Advanced Design Suite. I calculate 69,227Btu heat loss on 42000 sq. ft. including finished basement which is 4’ below grade. I for convenience used the default choice of International Falls, MN heating degree days of 10,000+. Previously I had used SlantFin and our actual 9028 heating degree days and calculated 90,932. Are these differences possible?

I am sizing for the worse but this may be a good argument for variable speed pumps?

 

[Nofossil]

No experience with the Uponor tool, but Slantfin seems to be somewhere between dead-on and about 20% high. There are a LOT of things that are very hard to get solid values for, so it makes sense to assume that actual loss may be a bit higher than pure theory would tell you - that seems to be the approach that Slantfin has taken.

By the way - 42000 square feet is one heck of a house!

 

[Sawyer]

No experience with the Uponor tool, but Slantfin seems to be somewhere between dead-on and about 20% high. There are a LOT of things that are very hard to get solid values for, so it makes sense to assume that actual loss may be a bit higher than pure theory would tell you - that seems to be the approach that Slantfin has taken.

By the way - 42000 square feet is one heck of a house!

Thanks Trevor, glad to know SlantFin is a reliable program. I had best make sure I did not enter 42,000 or 420 sq./ft in the Uponor program

I am going to call Uponor today to discuss my results with their program, perhaps I am doing something wrong. Their program does spell out specific R values for window, door, and air exchange as well as insulation R value and specific basement design.

 

[Nofossil]

To avoid confusion, Nofossil and Trevor are not the same person.

Wouldn't want Trevor to get blamed for my mistakes.....


Bill 'nofossil' Kuhns

 

[Sawyer]

To avoid confusion, Nofossil and Trevor are not the same person.

Wouldn't want Trevor to get blamed for my mistakes.....


Bill 'nofossil' Kuhns

Sorry Bill,

I did talk to Uponor and their design people said in a house with 2200 ft up and down, a half underground basement, modern insulating and sealing methods that 69,000 Btu heat loss would not cause a red flag. This winter will tell!

George

 

[Nofossil]

I did talk to Uponor and their design people said in a house with 2200 ft up and down, a half underground basement, modern insulating and sealing methods that 69,000 Btu heat loss would not cause a red flag. This winter will tell!

George

Back in the old days when spreadsheets were made on stone tablets, I did my own version of the Slantfin / Uponor tool. I plugged in all the heat losses, added infiltration based on physics and test data, and came up with 30,000 BTU peak heat load for my 3500 square foot house (three levels including a walkout basement). Turned out to be almost exactly correct. Only mistake was that I put in enough baseboard to deliver only about 35,000 BTU - 52 feet. It's worked for 20 years - I can maintain temperature, but I can't change it when it's cold outside. No setback thermostats for me. I'm adding a radiant zone under the main floor which should help.

 

[solarguy]

Radiant heat design calculation programs are different, 10 degree delta, hot water baseboard calcs, 20 degree delta.
If you have baseboard, go with the slantfin number.

 

[DaveBP]

Air infiltration figures are a Major wildcard in heat load estimates. It is a large fraction of the total load on most houses, majority factor in some of the old farmhouses. Fortunately, it is easy to do. Just hire your friendly local energy audit outfit to come out with their IR scanner and blower test-door setup and they will give you very precise and useful numbers for the software to use. Current cost here in S Maine is about $500. Maybe that's why I don't know anybody who's had it done?

 

[Sawyer]

Radiant heat design calculation programs are different, 10 degree delta, hot water baseboard calcs, 20 degree delta.
If you have baseboard, go with the slantfin number.

I am new to this so pardon my ignorance, why is heat loss different with radiant than baseboard? I thought the programs were measuring the heat loss of the building, not the source of the heating supply.

 

[Sawyer]

Air infiltration figures are a Major wildcard in heat load estimates. It is a large fraction of the total load on most houses, majority factor in some of the old farmhouses. Fortunately, it is easy to do. Just hire your friendly local energy audit outfit to come out with their IR scanner and blower test-door setup and they will give you very precise and useful numbers for the software to use. Current cost here in S Maine is about $500. Maybe that's why I don't know anybody who's had it done?

Dave we have a small electric coop where I live, still better than the generator!

When I had all my plumbing and electrical finished and all ceilings sheeted with OSB I had an insulation company come to seal and insulate. They foamed all outside outlets and faucets 12"x12", and all doors and windows, then any penetrations through the plates from electrical and plumbing. When they were finished they sprayed the wall with Applegate adhesive cellulose which filled all spaces around those difficult piping and electrical locations, finally blowing the scissor trusses and flat areas to R44. With all the siding caulked and the house wrapped it is very air tight, even those 30-40mph winds are not felt at the outlets and door and window edges. Our old house was a pre-1900 farmhouse and I swore when I built this there would be a lot of changes.

 

[Sawyer]

Air infiltration figures are a Major wildcard in heat load estimates. It is a large fraction of the total load on most houses, majority factor in some of the old farmhouses. Fortunately, it is easy to do. Just hire your friendly local energy audit outfit to come out with their IR scanner and blower test-door setup and they will give you very precise and useful numbers for the software to use. Current cost here in S Maine is about $500. Maybe that's why I don't know anybody who's had it done?

Dave we have a small electric coop where I live, still better than the generator!

When I had all my plumbing and electrical finished and all ceilings sheeted with OSB I had an insulation company come to seal and insulate. They foamed all outside outlets and faucets 12"x12", and all doors and windows, then any penetrations through the plates from electrical and plumbing. When they were finished they sprayed the wall with Applegate adhesive cellulose which filled all spaces around those difficult piping and electrical locations, finally blowing the scissor trusses and flat areas to R44. With all the siding caulked and the house wrapped it is very air tight, even those 30-40mph winds are unfelt at the outlets and door and window edges. Our old house was a pre-1900 farmhouse and I swore when I built this there would be a lot of changes.

 

[pybyr]

To avoid confusion, Nofossil and Trevor are not the same person.

Wouldn't want Trevor to get blamed for my mistakes.....

Bill 'nofossil' Kuhns

Thanks Bill/ Nofossil- I appreciate that you want to be sure that I receive credit only for my own mistakes signed, pybyr/ Trevor, who takes it as the utmost compliment (and I mean that very sincerely) to have anyone confuse me with Nofossil, who's been at all this a lot longer than I have!

 

[BrownianHeatingTech]

I am new to this so pardon my ignorance, why is heat loss different with radiant than baseboard? I thought the programs were measuring the heat loss of the building, not the source of the heating supply.

You're correct - heatloss is not related to the heat source, except in some very specialized situations.

The differences between the programs are related to different safety factors.

Joe