1800 sq ft well insulated house, a little north of NYC, 40kbtu heat loss, three zones: basement baseboard, main and 2nd floor large cast iron rads.
1. How would one factor in that fact that main and second floors are each piped in series. 6 and 4 rads respectively? My guess is that a)this is not worth re-piping into direct return, monoflo etc, and that b) any delay of heat or imbalance has been unnoticeable in such a small house.
2. Our side porch is very poorly insulated, with three external walls, two of which are brick and has two inadequate Governale radiators. It is always 15 degrees colder than the rest of the house. We leave it that way. In a heat loss some years ago this room factored in at 10K of the 40K heat loss. So when I do a new real-time heat loss based on btus used and degree days, I'll have to add in btus to know what the usage would be if I heated that room--maybe with some insulation put in--to the same temperature as the rest of the house, which in our case is 65degrees. But I will probably factor in a new inside set point of 75º as a worst case scenario.
3. We just had our attic rafters closed-cell spray foamed--now unvented. R36. With my original heat loss, I factored in a cold ceiling of .110 given that the attic floor had some fiberglass insulation. So now do I no longer call that a cold ceiling given the foam above it? Or still factor in a less cold ceiling since some house heat is still going to heat the attic's conditioned space to about 3 degrees colder than the rest of the house. (Most of the very old fiberglass is still in the attic floor but with plenty of upward leakage.)
4. On the internet I ran into Robert C. Obrien's 'real time' heat loss method http://mechanical-hub.com/sites/hydronics/heat-loss-calculation-on-every-residential-boiler-replacement/ which bases the loss on actual usage per heating degree day over a certain time period. I think others have promoted this as well. I love the idea since it cuts through so much guesswork. So I multiplied my 777 therms used for heating last year X 100kbtus per therm = 77,700,000btus X .75AFUE old boiler = 58,275,000btus/4995 degree days = 11,667btus per DD/24 hours = 486.111 btus per Heating Degree Hour/1800 sq ft X 65 (differential between set point of 65º and 0º design temp) = 31,600 btu/hr. And this is conservative since design temp here is really more like around 13ºF. On the other hand I'd probably want to raise the set point to 75º and account for that cold porch. So my question is: Does this method really tell you if you'll have enough heat on a design day? In looking for a boiler replacement in two years, contractors are already ballparking me in emails for a 155Kbtu boiler which seems nuts. Our boiler is under-fired at 170kbtu and with all our new insulation I'm worried we'll be short-cycling and condensing too much. Our heating savings are around 33% since the foam insulation. No one can believe a house actually has a 30K heat loss. Which leads me to my last question:
5. With any new boiler we would get an indirect hwh. Our potable water btu requirements are about equal to the heat loss, though I'd probably want to get a boiler that netted at least 40-50kbtu to cover the series piping, higher indoor temps, cold porch, etc. (Our current 10 yr. old stand alone 40gallon gas hwh nominally fires at 40kbtu, but I measured the gas meter dials and found it closer to 30K.) Our hot water is more than enough for my wife and I. So seems to me net 50kbtu boilerworks, yes? Which would be about 74Kbtu firing rate.
1. How would one factor in that fact that main and second floors are each piped in series. 6 and 4 rads respectively? My guess is that a)this is not worth re-piping into direct return, monoflo etc, and that b) any delay of heat or imbalance has been unnoticeable in such a small house.
2. Our side porch is very poorly insulated, with three external walls, two of which are brick and has two inadequate Governale radiators. It is always 15 degrees colder than the rest of the house. We leave it that way. In a heat loss some years ago this room factored in at 10K of the 40K heat loss. So when I do a new real-time heat loss based on btus used and degree days, I'll have to add in btus to know what the usage would be if I heated that room--maybe with some insulation put in--to the same temperature as the rest of the house, which in our case is 65degrees. But I will probably factor in a new inside set point of 75º as a worst case scenario.
3. We just had our attic rafters closed-cell spray foamed--now unvented. R36. With my original heat loss, I factored in a cold ceiling of .110 given that the attic floor had some fiberglass insulation. So now do I no longer call that a cold ceiling given the foam above it? Or still factor in a less cold ceiling since some house heat is still going to heat the attic's conditioned space to about 3 degrees colder than the rest of the house. (Most of the very old fiberglass is still in the attic floor but with plenty of upward leakage.)
4. On the internet I ran into Robert C. Obrien's 'real time' heat loss method http://mechanical-hub.com/sites/hydronics/heat-loss-calculation-on-every-residential-boiler-replacement/ which bases the loss on actual usage per heating degree day over a certain time period. I think others have promoted this as well. I love the idea since it cuts through so much guesswork. So I multiplied my 777 therms used for heating last year X 100kbtus per therm = 77,700,000btus X .75AFUE old boiler = 58,275,000btus/4995 degree days = 11,667btus per DD/24 hours = 486.111 btus per Heating Degree Hour/1800 sq ft X 65 (differential between set point of 65º and 0º design temp) = 31,600 btu/hr. And this is conservative since design temp here is really more like around 13ºF. On the other hand I'd probably want to raise the set point to 75º and account for that cold porch. So my question is: Does this method really tell you if you'll have enough heat on a design day? In looking for a boiler replacement in two years, contractors are already ballparking me in emails for a 155Kbtu boiler which seems nuts. Our boiler is under-fired at 170kbtu and with all our new insulation I'm worried we'll be short-cycling and condensing too much. Our heating savings are around 33% since the foam insulation. No one can believe a house actually has a 30K heat loss. Which leads me to my last question:
5. With any new boiler we would get an indirect hwh. Our potable water btu requirements are about equal to the heat loss, though I'd probably want to get a boiler that netted at least 40-50kbtu to cover the series piping, higher indoor temps, cold porch, etc. (Our current 10 yr. old stand alone 40gallon gas hwh nominally fires at 40kbtu, but I measured the gas meter dials and found it closer to 30K.) Our hot water is more than enough for my wife and I. So seems to me net 50kbtu boilerworks, yes? Which would be about 74Kbtu firing rate.