Introduction and Heat-Loss Calc Questions

camp10

Hi guys,
My name is Sean, I live a little bit south of San Francisco, and I am beginning to plan the replacement of my forced air heating system for a radiant system using Runtal radiators. I have read many helpful threads over the past month, thanks to all the professionals here providing great knowledge and advice in this public forum.
I recently hired a Professional Engineer to do a heat-loss calc on my house, he was recommended by my architect and has been engineering mechanical systems and providing Title 24 analyses for 34 years. I was surprised when he provided me with the heat-loss numbers, he told me he rounded up the numbers by 40% to allow for "piping losses, start-up loads, and a general safety factor." So, as I move forward and begin to size my radiators (I'm trying to stay around 140*F SWT), what numbers should I use? For those of you that have designed these types of systems, do you build in a "general safety factor"?

KC_Jones

camp10 said:

Professional Engineer
he told me he rounded up the numbers by 40% to allow for "piping losses, start-up loads, and a general safety factor."

Those 2 things don't go together. I could understand a little bit of safety maybe, but 40% is asinine. If he has that little confidence in his numbers I would have that little confidence in him.

Out of curiosity what is the square footage of the house and what is the heatloss number he gave you?

camp10

KC,
The square/ft of the house is 1,248, with the living area above the same sq/ft of the unfinished garage/basement below. With the built in "safety factor", the heat loss for the house is 38,600Btuh. He used current architectural plans from our remodel this year, and prepaired the calculations on EnergyPro 7.1 software. He used the ASHRAE outdoor design temps for winter, 29*F for Belmont, Ca.

Brewbeer

Is your forced air system fired using natural gas? If so, it is possible to estimate actual heat loss using gas consumption and heating degree day records.

With a 1,300 sq.ft. house and a 29 degree design temp, the only way the house is anywhere near a heat loss of 38,000 BTUs is if it is 50%+ glass.

Jamie Hall

You shouldn't need that safety factor -- if the system itself is properly designed, built, and installed. However, if he can't control those aspects of the job, I can see why he might want it.

camp10

Brewbeer said:

Is your forced air system fired using natural gas? If so, it is possible to estimate actual heat loss using gas consumption and heating degree day records.



With a 1,300 sq.ft. house and a 29 degree design temp, the only way the house is anywhere near a heat loss of 38,000 BTUs is if it is 50%+ glass.

Yes, the forced air furnace I will be replacing is fired using natural gas. I am unable to calculate using gas consumption because we have been heating the house with the furnace blowing hot air in the garage/basement for the last two years. (Long remodel where I had to partially disconnect the furnace and a very forgiving wife ). Our house is very typical of California construction, vintage 1947, there are no walls of glass.

camp10

Jamie Hall said:

You shouldn't need that safety factor -- if the system itself is properly designed, built, and installed. However, if he can't control those aspects of the job, I can see why he might want it.

I am thinking this is most likely the case. I plan on doing this project myself, and he may have been a little uneasy about this not knowing me. My dad is a mechincal contractor, 44 years as a steamfitter/pipefitter with 20 years as a union fitter in San Francisco, and 24 years as a contractor. He has done many commerical boiler installs , just never for residential and never a mod/con that I plan on installing. I plan on dragging him into the 21st century with this project, he still loves his steam systems and pneumatic controls.