Boiler Sizing.....

Joe_20

I've been kicking around radiant heat for a couple years. Been working with a plumbing outfit that did a heatloss calc and recommended an Ultra 155...The calculations show 75,000btu / hour heat loss. I also ran numbers through a Slant Fin spread sheet that showed similar heatloss. At the time the Ultra was only available in an 80, 155, and 230 model...now there's a 105 available....would that be large enough given the 75K heat loss and DHW 60 gal? My concern is short cycling....what's the rule of thumb on these things...safety factors and the like...or doesn't it matter since they modulate....It's looking like 6zones 3/8 pex with extruded plates under the floor and basically the same for the existing basement....3/4" t&g on 2X4 stringers with blue board stuffed in-between...tubing ran in channels in the blue board.....
Also kicking around Munchkins, but I think the Ultra has much more to offer....

Weezbo

i am off to an ultra class todday ,all i have to do is....

tie three i series valves, a headder ,plumb the water rough in and finish some roughin on the abs ,go get the materials for the two new duplexes we need to get started on and finish an elevated dishwasher ....summer isnt quite..."Here" yet ...Thanks for asking...as for me...i am holding out for a modulating condensing buderas oil fired..

Constantin

Well, if the house has a 75kBTU heat loss...

... then logic dictates that an appliance with at least 75kBTU DOE output be installed. If you have a lot of confidence in your numbers, a Munchkin T80 could be a great choice. The Ultra 105 would be the next step up, IMHO. Both the T80 and the Ultra 105 have 5-1 turndown ratios, which allow them to modulate pretty far down...