Davie
Member
Hi all,
I'm doing a reno of my 100-year old, semi-detached, 2-storey, double-brick Edwardian house, and I intend to replace the existing forced air system with an in-floor radiant system. The house is 500sq.ft. per level with an unfinished full size basement. (So 1000sq.ft. of living space, plus 500 in the basement.)
I have done heat loss calculations for the whole thermal envelope of the house, and have come up with a value of 59,000Btu/h based on a design temperature of 1F, desired indoor temperature of 70F, and an estimate of 2.2 air changes per hour. (I chose the air changes/h value based on the age of the house, its poor air sealing and on currently having two old fireplaces which I plan to seal up eventually.) In the basement I plan to heat with radiators. For the first and second floors, I plan to use oxygen barrier PEX and aluminum heat deflectors stapled up to the subfloor from beneath and insulated.
The heat loss value for the basement is 10,000Btu/h, and the above ground area is 49,000Btu/h. Divide that number by 1000sq. ft. and I find an average of 49Btu/h/sq.ft. heating requirement for the in-floor system. My room by room calculations, however, show that it's not so evenly distributed. Several of the colder rooms require values in the high 50s or even 60Btu/h/sq.ft. Additionally, not every square foot of floor space is useable, nor does each emit a full value of its potential--for instance the areas under heavy furniture and an unheated area under the pantry.
I have read that the ideal maximum comfortable floor temperature for sustained contact is 85F, with temperatures of 90F or even up to 92.5F being acceptable in areas of low traffic and short sustained contact, like bathrooms, closets, possibly even bedrooms. With a desired indoor indoor temperature of 70F, a 92.5F floor offers 45Btu/h/sq.ft., but 85F only offers 30Btu/h.sq.ft. If I dropped to 68F indoor temperature, I could get 49Btu/h/sq.ft. from 92.5F floors, but that still leaves a lot of heat lacking for the rest of the house. At 70F I would need a floor temperature of 98F to get the 56Btu/h/sq.ft. that I need in the Kitchen and 100F for the 60Btu/h/sq.ft. needed in the 2nd bedroom.
Which brings me, at last, to my question: Am I going to have to add baseboard radiators, or some other kind of additional heating to get what I need? I am under the impression that similar old homes in Toronto, similarly uninsulated, are heated with radiant floors floors alone. Do those people run 100F floors? If I do need to add additional heating, will the baseboards need to operate at a different water temperature than the floors? Is there something that I'm missing?
I wonder if I am just in a hard spot because of how poorly insulated my century home is (the 8" brick walls with lathe and plaster are R3.9).
I don't feel completely in over my head here, but I am certainly not looking to add complexity where it may not be needed.
I'm doing a reno of my 100-year old, semi-detached, 2-storey, double-brick Edwardian house, and I intend to replace the existing forced air system with an in-floor radiant system. The house is 500sq.ft. per level with an unfinished full size basement. (So 1000sq.ft. of living space, plus 500 in the basement.)
I have done heat loss calculations for the whole thermal envelope of the house, and have come up with a value of 59,000Btu/h based on a design temperature of 1F, desired indoor temperature of 70F, and an estimate of 2.2 air changes per hour. (I chose the air changes/h value based on the age of the house, its poor air sealing and on currently having two old fireplaces which I plan to seal up eventually.) In the basement I plan to heat with radiators. For the first and second floors, I plan to use oxygen barrier PEX and aluminum heat deflectors stapled up to the subfloor from beneath and insulated.
The heat loss value for the basement is 10,000Btu/h, and the above ground area is 49,000Btu/h. Divide that number by 1000sq. ft. and I find an average of 49Btu/h/sq.ft. heating requirement for the in-floor system. My room by room calculations, however, show that it's not so evenly distributed. Several of the colder rooms require values in the high 50s or even 60Btu/h/sq.ft. Additionally, not every square foot of floor space is useable, nor does each emit a full value of its potential--for instance the areas under heavy furniture and an unheated area under the pantry.
I have read that the ideal maximum comfortable floor temperature for sustained contact is 85F, with temperatures of 90F or even up to 92.5F being acceptable in areas of low traffic and short sustained contact, like bathrooms, closets, possibly even bedrooms. With a desired indoor indoor temperature of 70F, a 92.5F floor offers 45Btu/h/sq.ft., but 85F only offers 30Btu/h.sq.ft. If I dropped to 68F indoor temperature, I could get 49Btu/h/sq.ft. from 92.5F floors, but that still leaves a lot of heat lacking for the rest of the house. At 70F I would need a floor temperature of 98F to get the 56Btu/h/sq.ft. that I need in the Kitchen and 100F for the 60Btu/h/sq.ft. needed in the 2nd bedroom.
Which brings me, at last, to my question: Am I going to have to add baseboard radiators, or some other kind of additional heating to get what I need? I am under the impression that similar old homes in Toronto, similarly uninsulated, are heated with radiant floors floors alone. Do those people run 100F floors? If I do need to add additional heating, will the baseboards need to operate at a different water temperature than the floors? Is there something that I'm missing?
I wonder if I am just in a hard spot because of how poorly insulated my century home is (the 8" brick walls with lathe and plaster are R3.9).
I don't feel completely in over my head here, but I am certainly not looking to add complexity where it may not be needed.
