Heat loss calc

Paul S_3

This is my first whole house heat loss calc. I am installing a brand new loop hot water system....i just finished the upstairs part of the house.....and i only have about 15,000 btu's of loss.....there was a 105,000 btu warm air furnace in there before....by the time i finish the first floor i will be no where close to the btu's of the furnace.....i understand it may be smaller for ex. 60-80,000btu....am i doing something wrong....do i get a unit that equals what my calculation is..?

Gordy

That's why

Doing one is so important. Double check your calculations, and do not go by existing equipment. The other guy may have not done one, and installed an oversized heat source to cover it. No one complains about enough heat, but these days they complain about high utilities.

Paul S_3

Thanks

Thanks....they ask for certain insulation....for example r-11....r-18.....i really do not know what type they have in the home.....house was built in 60's....if that helps.....how do i put correct insulation in calculation....without actually seeing what was used.?

icesailor

"R" value in walls:

Do it multiple ways.

Use R-11 which is insulated, even if you aren't sure what may be there.Then calculate it at R-7 which  is maybe  2" of insulation. Depending on when and where the house was built in the early or late 60's will have some bearing on how much insulation was used. If you go with the lesser insulation, it just means that you need more radiation. It doesn't take that much more radiation to cover it when done accurately.

Check attic insulation. If insulation has been added, it won't be the same as the insulation that is under the new. If the under/first insulation is 6", you can probably guess that there is at least 3" in the walls. If there is only 3 1/2", there probably is only 2" in the walls.

If you really want to know, there are places to look. Like if you have a dryer vent that goes through a frame wall that is finished on a heated wall, pull out the dryer vent and look up to see what insulation is there. Unless it was a renovation where the wall was ripped down in the past and re-insulated, that's probably what is in the rest of the house.

I never get too nuts about it because most round UP and not off or down. If the calculation calls for 6.3' of radiation, I'm going to put in 7'. I'm not going to cut 9" off a 7' heater.

There's a fudge factor. Use it.

SWEI

more radiation

Means lower water temps, which produce higher efficiency with a mod/con boiler.  Upsize where you can, but pay attention to balance.  If you upsize all but two rooms you are going to have comfort issues.  Don't be afraid to specify different indoor temps for some spaces.  Bedrooms with elderly or infants living in them and bathrooms will benefit from a little more output.  I typically spec those at 72-75F when the rest of the house is at 68F.  Infrequently occupied spaces like workshops or basements can be quite a bit lower in many cases.

Paul S_3

does

anyone know a good heat loss calc. program on the internet.....i use one out of a I=B=R Book....

Paul48

Slant/Fin

is probably the simplest..  http://www.pvsullivan.com/Downloads.html

Paul S_3

thanks

thanks for the link

icesailor

Slant Fin/IBR

The Slant Fin heat loss calculation program uses the IBR method. If you have the old H22 heat loss guide, it is the same. The new one is different.

SWEI

new one and old one

There's a new Slant/Fin app too http://www.slantfin.com/index.php/professionals/heatloss



If they offered a version for Android, I'd give it a try.