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  1. #1

    Undersizing the furnace?

    Hi all,
    I am new here, so bare with me
    We have bought a new house with 22 yo furnace 100,000 BTU in Ontario, Canada.
    The house is rented as 2 floors (main+basement) to 2 families.
    The house is probably build in 70s

    We had few contractors coming over to give us the quote and get a different story all the time.
    Most recommented 60BTU furnaces, where one did some extensive calculations and recommended 40BTU. The main floor is 1000 sq feet, the basement is probably 600-700. The price is same between 40BTu and 60BTU. I am concerned taht we are significantly undersizing the furnce if we go with 40,000BTu's. And since I have tenants there it makes it even worse if they start complaining that it is too cold.
    I think the house has very-very basic insulation in it.
    What do you guys think?

  2. #2
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,058
    IT is possible that the original is much to large, I would go with the load calculation.

    How are you separating the control of the furnace with two tenants?

  3. #3
    I am not separating. The house was never designed for 2 heating circuts. The main floor tenant controls the heat.

  4. #4
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,058
    Doesn't seam fair to the tenant in the basement. What happens if they have a feud?

  5. #5
    I am not sure if I have options...... Any suggestions are welcome. But I do not want to redo all ventilation system just becuase of that. I guess they can close some vents or open the window......

  6. #6
    Join Date
    Aug 2000
    Location
    Central Oregon
    Posts
    749
    Make sure they consider the larger ducting when installing a furnace with a lower cfm. Issues may arise from low or no air flow to areas.
    If you think our goverment is screwed up. You haven't lived in another country.

  7. #7
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,139
    Navipro

    Basements below or partially below grade usually have small load requirements.

    What are typical winter lows for your area/climate?

    Where is furnace currently located?

    Can dealer install a high eff condensing furnace?

    Both Rheem/Rudd have a nice two stg var speed 95% eff furnace that might be good fit. As I recall, low stg in high 30s BTU, high stg around 45 KBTUs.

    Post back.

    IMO

  8. #8
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    IF the one guy did a load calc and it supported 40k BTU"s then that's probably all it needs. 160sqft on 2 floors isn't very large. SInce it's two floors, it's not going ot need as mcuh heat as a single story 1600sqft home sicne it has a single roof 1/2 as big. half the property is underground. I'd bet the load cal called for seomthing like 35-40k BTU's.

    For splitting the system. It might be possible to install a simple zone control system and just not use and dampers. That way at least each area can "Call" for heat independently... then if it's too warm most of the time the tenants can partially close a couple dampers. IF you're paying for the heat, you don't want them opening windows.


    Another option is getting a thermostat that has the option for a remote indoor sensor. It can at least average the two temperatures so you will at least split the difference.

  9. #9
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,608
    what if one is cooking some smelly food

  10. #10
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,400
    burnerator,

    This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

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  11. #11
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,881
    Especially if you're paying the fuel bill, I'd have a Home Energy Efficiency Audit performed so you could also get the first floor closer to the basement's heating requirements.

    Also helps get the heatloss calc more accurate. I'm estimating the outdoor design is about one degree F. (?) You need to get that heatloss calc accurate, with a correct margin of called-for over capacity.

    Some utility companies have Audit programs...

    I'd also go with:
    motoguy128 IF the one guy did a load calc and it supported 40k BTU"s then that's probably all it needs. 1600sqft on 2 floors isn't very large. Since it's two floors, it's not going to need as much heat as a single story 1600sqft home since it has a single roof 1/2 as big. half the property is underground. I'd bet the load cal called for something like 35-40k BTU's.

    For splitting the system. It might be possible to install a simple zone control system and just not use and dampers. That way at least each area can "Call" for heat independently... then if it's too warm most of the time the tenants can partially close a couple dampers. IF you're paying for the heat, you don't want them opening windows.

    Another option is getting a thermostat that has the option for a remote indoor sensor. It can at least average the two temperatures so you will at least split the difference.

  12. #12
    Quote Originally Posted by tigerdunes View Post
    Navipro

    Basements below or partially below grade usually have small load requirements.

    What are typical winter lows for your area/climate?

    Where is furnace currently located?

    Can dealer install a high eff condensing furnace?

    Both Rheem/Rudd have a nice two stg var speed 95% eff furnace that might be good fit. As I recall, low stg in high 30s BTU, high stg around 45 KBTUs.

    Post back.

    IMO
    Hi and THANK YOU fo all the responses!!!!

    Some answers
    Winter lows are around -5F, historically it went down to -20F
    Furnace is in the basement.
    We are only concidering 95.5% eff furnace (condencing)
    It is one of the York models

    For splitting the system. It might be possible to install a simple zone control system and just not use and dampers. That way at least each area can "Call" for heat independently... then if it's too warm most of the time the tenants can partially close a couple dampers. IF you're paying for the heat, you don't want them opening windows
    I am not sure if I follow. Are you refering to the vents where the air is coming out of? If yes, then they all are "closable", so, yes, this is one of the ways to control the temperature.

  13. #13
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,881
    Motoguy128 is talking about dampers in the branch ducts where they take-off of the mains, not at the diffuser/registers.

    He is talking about a Zone Control System & NOT using dampers or closing off registers. It should work well in your situation.

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