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Is this new boiler big enough?
Bruce H.
Member Posts: 3
I just bought a 3 family building that has a pump assisted gravity hot water system. I had a oil to gas conversion done, replaceing the entire boiler. This may seem like a stupid question but how can I tell if the new boiler was sized correctly? Since I live in NYC. it is not that cold yet but I would like to be able to juge the performance of the system now .
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Comments

size
If you have radiators you need to figure out what the total edr is of all the raditors. likewise if its baseboard you need to add the total feet of fin radiation and convert to BTUs. in dans book section he has a book that tells you how to do this.its called The Golden Rules of Hydronics. get the book its very easy to use,it will help you size you boiler.
joe.g.0 
Sorry, some disagreement here
On a hot water system, the boiler size should be based on the heat loss of the home, not the size of the radiation. This is a little harder to figure out. The R values of all the exterior surfaces must be determined, thier area, and the rate at which the home leaks air. Basing the size of the boiler on the radiation for a hot water system will often give you a boiler twice as big or more as it should be. In my own 2800 sq ft 1906 home near Chicago, basing the boiler size on radiation would result in a boiler of about 200,000 btu/hr input. Basing it on heat loss, the boiler size is about 80,000 btu/hr input. A boiler too big reduces comfort, increases you fuel bills, increases service needs and reduces equipment life due to excessive equipment cycling. On the other extreme, it is extremely rare that a boiler does not have enough capacity.
Boilerpro0 
A question Boilerpro,
If the radiators require 200,000 btu's but the house only 80,000, how do you tell the btu's to go where they belong?
It seems the process is more complicated than just doing a heat loss if the existing radiators are to remain.0 
Water temperature changes
Radiation capacity is based on the temperature of whatever the stuff is that fills it..... usually plain water or steam. For water the common standard is 170 avg radiator temp with 70F air...typically 180F into the rad and 160F out. In my home, if all the radiators were at 170F they would give you about 135,000 btu/hr output (200,000 btu/hr input boiler). Now if those same radiators only needed to produce 56,000 btu/hr output(80,000 input boiler, then the radiators could run cooler. In this case about 110F. The water still can move through the radiators at the same rate, but the water temp and radiator output would be much lower. On a side note, the water flow can be reduced too, and then the flow of water usually needs to be balanced using the radiator valves. Hope this makes things a little clearer.
Boilerpro0 
A boiler allready has been installed and all I want to be able to judge is if it is going to have enough capacity when it gets really cold out side?0 
Slant Fin
> A boiler allready has been installed and all I
> want to be able to judge is if it is going to
> have enough capacity when it gets really cold out
> side?
0 
Slant Fin
has a free heatloss program . Its very simple to use , and you can see if the boiler is sized to the heatloss of the house . Click on Free Heatloss Calcs  to the left in the topics .0 
here is a way, but it may get warm
this is directly from my HOFFMAN DATA BOOK 1934assuming you'll want 70 degrees inside at 0 degrees outside, turn your boiler on, jump the tstat wires so it stays on, if the present outside temperature is 10 degrees you should be able to reach 76.7 inside the house. if the present outside temp is 20 degrees you should be able to reach 83.4 degrees inside. if the present outside temp is 30 degrees you should be able to reach 90.1 degrees inside. if the present outside temp is 40 degrees you should be able to reach 96.8 degrees inside. if the present outside temp is 50 degrees, you should reach 103.5 degrees inside.if the present outside temp is 60 degrees you should be able to reach 110.2 degrees inside.70 degrees ouside would be 116.9 degrees inside....really want to test it...you can...gonna get hot tho:).0 
heat loss
Ask the installer for a copy of the heat loss calculations he ran when sizing your new boiler. If he didn't do one, ask how he sized it. Expect responses like "same size as old one" or "I've been doing this so long I can tell without doing a heat loss calc".
As others have suggested, there are various free or inexpensive programs available that let you do your own calculations, with at least enough accuracy to see if you're in the ballpark.
Mark0 
Thanks
0
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