Boiler sizing

Constantin · March 2006

... because anecdotal evidence shows that the heat losses calculated by programs are inflated by about 25%. Given that you're below the limit on a design day, you ought to be OK, as long as the boiler does not have to be de-rated due to high return water temperatures on a design day.

Wayco Wayne_2 · March 2006

Have been asked

to bid on a boiler change out. The customer has done a lot of research and is interested in the Prestige from Tri Tube. I did the heat loss for 10 degrees outside temp although for my area (wash dc) Ashrae says to use 15 degrees. I come out with a software based guessimate of 96000 at 10 degrees. At 15 degrees 88,000 is required As some of you may know the output of the smallest Prestige is 99,000. There's not a lot of cushion there. The next size Prestige is a 157,000 output. Which boiler would you use and why? WW

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Brad White_9 · March 2006

Good answer, Constantin.

All around.

[Deleted User] · March 2006

Go small...

Heat loss calcs miss SO much real time stuff that will cover your butt it's not funny.

I just did a real time energy audit on an older property in Denver for a Wallie, and the house boiler was sized at 750K. Anyone with "boiler replacement" glasses on would replace like with like. THe run time audit, at design conditions, found that the real time load was only 350K.

Go small, you'll be just fine.

ME

Wayco Wayne_2 · March 2006

Thank you

for your input, and support. I sort of knew to go small but it makes me nervous. What if........ there's some weird thing with the house not evident, kind of insecurity. It doesnt help that the existing beastie is 240,000 btuh. It's an old house with old gravity pipes and over sized cast iron rads. The kind of job that could save a homeowner big money, if they go mod con. WW

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

John Ketterman · March 2006

See if they will show you last month's gas bill. Maybe you can calculate how many BTUs they now use per hour per degree day, then scale it up to 55 degree-days (10F). I bet you will find that Constantin is right, they're not using as much as your program says, even with the old boiler.

Mike T., Swampeast MO · March 2006

Trust yourself Wayne! Granted heat loss calculations are somewhat of a "guesstimate" but provided you know your stuff (it seems you do) and provide good data, you'll already have a "cushion" from the nature of heat loss calculations! Beyond that, you've decreased the design temp by 5 degrees.

No way to talk them into a condensing/modulating boiler? As you said, they'll save lots of gas!!!

Boilerpro_3 · March 2006

Mike,

The Prestige is a mod con

Boilerpro

gasfolk · March 2006

Real Time Load

Mark,

How do you size from real time loads? Do you add any safety margin? Do you worry about unusually cold weather? Besides sizing, does real time load help you in other ways?

Thanks,

gf

Boiler sizing

Comments

Categories