There's too much hot air in here!

We are finishing up design for a family room addition and kitchen renovation for a duplex here in Del Ray.  The City of Alexandria requires a design for the HVAC system when submitting for the permit and the addition is only going to add a net 150 s.f. to the house, so our plan was to replace the HVAC system with a better performing one and keep the same size.  We found during this process that this house has a very common problem many homes share.  The HVAC system is oversized. In this case...the existing heating system is about 200% the size it should be.  The existing furnace is 60,000 btu's and the design calculations we performed indicate it should be 30,000 btu's.

A properly sized system is determined by what is called a Manual J calculation.  It takes all of the components of the house into consideration to size the system.  Problem is, a correct Manual J calculation is rarely performed. 

So how does this effect you in your home?  Think of it this way...have you ever tried filling your kitchen sink with a fire hose?  Now this is an extreme example, but you get the picture.  An oversized furnace will blast the house with heat quickly and then cools down until the thermostat calls for heat again.  Ideally, you want a slower steadier heating cycle to maintain more consistent temperatures in your home.