Hi Everybody, I had a very interesting consultation yesterday with an HVAC engineer who came to my 4400-square-foot 1860s farmhouse to help me with planning my new heating system. As those of you who have read my previous posts know, one of the issues that I have been struggling with is whether or not my own heat-loss estimates (I’ve used SlantFin and HVAC-Calc) are correct. I want to know so that I can correctly size my future boiler(s). The engineer, whose company does heat-loss estimates, looked at my heat-loss data and told me: (1) that he thought my estimates are too low, and (2) that I shouldn’t bother hiring anyone to come do a heat-loss estimate. (Given that he stood to make some money if I hired his company, it was hard not to respect the honesty implied in this comment.) The reason for both of his answers: air infiltration. Not only did the engineer feel the heat-loss programs under-estimated my losses due to infiltration, but he then pointed out the near-impossibility of accurately estimating the extent of air infiltration for an old house like mine. And, he noted, air infiltration is a huge chunk of my overall heat loss. The engineer’s feeling was that the number of air exchanges per hour experienced by my house could only be figured as an educated guess. Additionally, this number would fluctuate significantly based on wind speed (and, if one side of my house is leakier than another) direction. His guess was that my old house might conceivably undergo three or even four air exchanges per hour! (I hope he’s wrong … and this is significantly higher than the figure given by many heat-loss calculators, even for old, leaky homes.) Interestingly, I went back to HVAC-Calc (this program and SlantFin gave me very similar heat-loss totals) and found that the program default for an older, leakier house is one air change per hour. Over-riding the defaults shows that each additional air change per hour adds about 50,000 BTU/hr heat loss to my baseline total (at one exchange/hr) of 120,000 BTU/hr. So, does anyone have any opinion about how many air exchanges a reasonably well-maintained 1860s farmhouse with storm windows and storm doors all around might have each hour? Thanks for the help…. Charlie and Razz

I have a 2 in one system with 2 zone heating at the moment no heat is being used it is only being used for hot water heating. I have had to several times already shunt the auto pilot inorder to get the realy in it to stay on and start heating the water. Is that the 1st sign it is going ?> I will replace it soon as possible, but just curious to know... especially since I am not a boiler person but have recently been testing my hand.