Best Value/Most Reliable boiler?

[Dana]

At an average water temperature of 140F the 14' of baseboard is emitting about 4500 BTU/hr and the boiler is out of the condensing zone, delivering about 7000 BTU/hr, so there is about 2500 BTU/hr (42 BTU minute) of excess heat going into the zones.

If there's 40lbs of water in that loop the temperature would have risen more than 10F during a continuous 15 minute burn, which makes me wonder if there are no check valves allowing the other zones to backflow a bit(?). If the zone were completely isolated it would stabilize at 160F-165F if burning continuously in a non-condensing mode. If it's stablizing at temps less than 140F it means there is probably other water being circulated in that loop coming from other radiation.

By running it at 140F+ it's not short cycling- it won't wear out the boiler, but you are giving up all of the condensing efficiency.

As an experiment try setting the post-purge to 5 minutes and watch how quickly the temperature drops when starting at ~140F.

 

[NY_Rob]

As you mentioned..... If your zone valves are directly connected to your t-stats- once they close due to t-stat hitting setpoint, post-purge just dead-heads your CH pump and no water will actually circulate. No real problem dead-heading an ECM pump (other than wasting electricity) but a regular split-cap pump may overheat if dead-headed for extended periods.

 

[Sponsor]

 

[Ron Beck]

Not to throw a wrench in this late in the game but look at the Burnham K2-WT080B. Priced right and has a 10:1 turndown which takes you to a minimum of 8k. Lower turndown greater fuel savings looking at Dana's baseboard output numbers.

 

[BirchwoodBill]

My contractor installed a wm97 70 boiler, it is stainless steel not aluminum. I also replaced the slant fin in the basement with European style baseboard that keeps it warm using 120f to 140f water temperature. Properly sized components is the key to comfort. I hired a professional to size the system, to avoid the contractor from over sizing things. His numbers were very close to Dana’s napkin math. We also installed a whole house humidifier. That allowed us to turn down the thermostats with out sacrificing comfort.