Boiler and Hot Water Heater - BTUs
I’m currently renovating a 3 family, 4 story brownstone. We’re converting it from oil to gas. Per our architect, the drawing shows the boiler room with a specfic 60k BTU boiler & a 40k BTU hot water heater. My contractor stated to me yesterday that these items are not big enough for a 3 family…
I’m currently renovating a 3 family, 4 story brownstone. We’re converting it from oil to gas. Per our architect, the drawing shows the boiler room with a specfic 60k BTU boiler & a 40k BTU hot water heater. My contractor stated to me yesterday that these items are not big enough for a 3 family – 4 story house. Help!!! Can anyone give me an idea of how many BTUs are required for a boiler and a HWH for this type of brownstone. Many thanks!
Check out http://brownstoner.com/forum/archives/2006/05/advice_on_new_b.html
and http://www.keyspanenergy.com/pshome/local/conversion_offers_ny_kedny.jsp
Thanks cmu & Master Plumber. Your comments have been very helpful. He will definitely need to go back to the drawing board.
I agree with the above poster’s comments. There are very specific methods to sizing a boiler.
Steam boilers are sized to the connnected load by measuring each radiator and converting its square footage into what we call “equivalent direct radiation”. Hot water, or hydronic, boilers are sized to the heat loss of the structure.
Domestic water heaters are sized by more flexible methods determined largely by the lifestyle of the occupants.
My opinion? 60,000 BTUs is likely a severe miscalculation.
Considering an 80% efficient boiler of that input will provide less than 50,000 BTUs at it’s output, it is best suited to serve a modest 1200-1300 square foot residence.
Back to the drawing board?
You should, thereoretically, have a heat loss calculation done. It will give you an accurate figure, and *eliminate the tendency of contractors to over-estimate* (to protect themselves.) btw, this is particularly true of central a/c; if you decide to install that, *insist* on a manual J calculation, no seat-of-the-pants stuff (google heat load calculation).
That said, my 4-story, 3000sqft, semi-detached house with good windows but no roof insulation, has a 150kB boiler(Keyspan recommended 180), with steam heat and is fine. Steam heat is less efficient than hot water also, so take that into account. So you should probably have something similar or smaller. If you’re insulating heavily, go lower.
For water heaters, it’s more complicated, not just btu figure, which affects the “recovery” rate (ie how quickly hot water restores after use). 3 family=3 full baths? you should have at least a 50gal high-recovery (65-75kbtu) or 75 gal normal (50-60kbtu). Power combustion water heaters are quite expensive and need electrical, normal ones do not, an interesting trade-off.