Flue Loss Ratings

bruce pirger

Still haven't installed the boiler...so many other jobs going on. Remember I'm the guy who wants to burn wood as primary heat and keep his slab at 70-80 degrees or so. Also have radiant between joist upstairs...which might be slightly warmer, but again, not anticipated much with wood burning (due to experimental evidence).

Seems to me, my boiler will primarily fire to just heat hot water in the indirect. I have 3 daughters...we take probably 10 showers a day in our house. Heat load calculations come in about 55,000-60K. The woodstove, buring now, does a great job at heating the house. The concrete is of course a little cold (in NY state).

It seems to me I'm best off with a smaller boiler, around 75K or so, and a larger indirect tank. A 50 gallon tank would probably be great, a little bigger maybe for when my girls hit the teenage years...(My father used to stand in the basement and turn off the hot water valve after 3 minutes...DON'T DO THIS! LOL)

I also plan to add an outdoor wood boiler someday...and I want to run outdoor reset (for when wood is NOT being burned inside)...and of course need indoor reset so as not to get blown out by the radiant and wood. The Tekmar 363 does this all nearly perfectly, and I have purchased this controller and various sensors.

So, my question...Heat losses to ambient. It seems to me that the majority of my boiler firing will be for DHW, not heat. (Well insulated slab, 2" thoughout, and insulated exterior wall as well). I plan to use a direct vent boiler, to reduce the flue losses and not have to worry about combustion make up air. I don't seem to see the informaiton regarding boiler losses to ambient space...assuming an ambient temperature of 60 degrees or so (air temp). Will my boiler cool off and require running just to keep it above the 140 minimum return temperature? This seems like a tremendous waste...especially all summer when exlusively DHW...and I wonder if this pushes me even more towards a no return temp limit boiler, such as a Vitola. The Vitodens matrix burner is indeed mighty impressive...I need oil...rotrix...those Germans always build great stuff.

So, does experience indicate that the boiler will have to cycle just for its own health? I'm looking at a Crown ODV-75...can't find specs on its losses to ambient. (or from other boilers). Obviously a function of the boiler insulation, temp and such.

What does experience say?

Thanks. Sorry for the rambling.