Hi all, 

I am a new energy modeler in Canada, and I am trying to figure out how to model an addition to an existing house. The addition will use the existing furnace. I was thinking I would only model the addition, but in the "Natural Air Infiltration" tab, I would enter in the volume for the entire house, and make sure that the output capacities for the existing HRV reflect the addition. Any thoughts? Has anyone modeled an addition in HOT2000 before? 


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Hi Kyla,

In HOT2000, you need to model the whole house.  Are you doing this from plans?  What's the purpose of modelling this?

Dave Baerg

Hi Dave, thank you for your reply!

The purpose of the model is to show code compliance for the addition. I am doing it from plans, but I don't have plans for the entire house, or assemblies for the existing walls. I ended up speaking to someone from Natural Resources Canada yesterday and she told me that walls that are adjacent to a heated space don't need to be modeled, so I took that to mean that I wouldn't have to model the entire house. I assumed it would be treated similar to a duplex. But in your experience that isn't the case?


No.  I think the person at NRCan didn't fully understand your situation.  One heating source means it's one house.  It's also important to distinguish between a duplex and a semi-detached.  Semi-detached houses have seperate heating and hot water systems and are separated by a vertical wall.  From what I understand, that's not the case here. 

If the addition is a seperate living unit but shares a heating system with the existing house, it's a duplex. But duplexes need to be modeled as one house, or more accurately, as a MURB.  Which would mean you need to assess the existing structure.

If your code is anything like the Ontario code (or maybe you are in Ontario), compliance would most easily be met using a prescriptive method - i.e. walls must be a certain R value, ceilings another, windows a certain U value, etc.  But it's probably best to talk to the municipal code official about that.

The other issue is wether or not the heat load of the new larger house be satisfied by the existing heating system. HOT can give you a design heat loss calculation, or you can get an HVAC designer to do the calculation.  But either way, somebody has to go to the house to assess the existing house.


Ah, I see. Thanks very much, Dave!

I agree. 99% of the time additions are best suited for the prescriptive method. No modeling needed.


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