boiler retrofit question

DD_5

When retrofitting a boiler and none of the heat emitters are changing, then you size the boiler to the Btu capacity of the existing emitters, in this case baseboard radiators...is this correct? It doesn't make sense to do a heat loss calc because the emitters are staying the same. This seems pretty straightforward or am I missing something?

Robert O'Brien

Steam

boilers are sized as you describe,hot water boilers are sized by heat loss.The amount of radiation is totally useless information in sizing

DD_5

hot water

so if its a hot water boiler retrofit onto an existing system you should do a heat loss calc?

CMadatMe

Boiler Sizing

The correct anwser is to do a heat loss. Who's to say the baseboard was sized to a  heat loss from its birth..

EricAune

Both!

Chris is right about the heat loss calc. IMHP.  I lean towards the calc and then take into consideration the actual emitters.  In most cases the installing contractor lined the walls with the stuff in an attempt to keep the call backs away.



Compare what is needed for load satisfaction and then figure what temps and rates can be run given the amount of baseboard.  If there is more baseboard than needed you will be able to lower the fluid temp. and save some money for the owner. 

Dave Yates (GrandPAH)

heat loss reveals criteria for setting outdoor reset curve

If you do a room-by-room heat loss AND compare that to the EDR of the room's heat emitters on a room-by-room basis, you'll know exactly what your highest and lowest requirements are for water-delivery-temperatures and can, therefore, dial in the best outdoor reset curve. The type of heat emitter and its characteristic heating curve will also dictate boundaries, but absent the heat loss - it's all just a shot in the dark while blindfolded after being spun rapidly in circles by a whirling dervish(G).



Makes a modcon purr like a contented kitten and pleases owners with increased comfort and lowered fuel consumption.



For systems that exhibit out-of-bounds heat emitters sized in odd ways that defy comprehension, or for rooms where the same level of comfort-conditioning is not warranted or wanted, thermostatic valves can be added to tweak comfort and enhance savings.

DD_5

whirling dervish yo

Great answers fellas! I can work with this. 

KAHOT

Interesting question.....

I have been in the hydronic side of the heating business for more than 17 years now. I am having trouble explaining to a "newbie" why we always size replacement boilers to the heating load and not the attached load. I learned this so long ago, I don't remember how to answer him. His concern is that the last of the baseboard would get too cold. What is a good way to explain what happens when the boiler is sized to the heat loss and not the attached load when there is too much live baseboard in the space(s). As in I know what is proper and I have always done it the right way, I just don't remember why it works that way and what happens in the system. Can anyone help me explain this to him?