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How to heat new addition

Posted by Bibimus (My Page) on
Sat, Feb 9, 13 at 8:50

Converting a Garage into living space. House will grow from 2000 to 3000 square feet. Already built a new garage so this space will never be converted back. Currently have forced air. Instead of replacing the furnace was told to put a second furnace to handle the new rooms. Current furnace is not in the center of the house so one side of the house is warmer then the other. If I go with another furnace, could I heat a few of the current rooms along with the new addition so each furnace would then heat about 1500 sq feet each? What would be the advantage and disadvantage of this approach?


Follow-Up Postings:

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RE: How to heat new addition

Is the garage an open living space? If so a mini split would be a good solution. It would provide both heating and cooling.

A 3000 sq. ft. house is large enough to warrant two furnaces. You may be able to configure the second furnace to heat the garage and other rooms. It would be highly dependent on the proximity of the garage and the other rooms in order to determine the feasibility. I would probably need to create zones for the garage and the other rooms in order to maintain consistent temperatures.

The advantage is you can get better temperature control on the rooms that are having temperature issues. The disadvantage is running new duct work and creating an over sized condition with the original furnace.

What size and efficiency is your current furnace? Have you done a heat load calculation? You current furnace may be able to handle the additional area.


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RE: How to heat new addition

The garage will be an open space. The current furnace is 5 years old and is 94% efficient. I know when we had it installed the installer stated it was sized correctly for this house but I do not remember what the size was. Both the previous and current furnace leave part of the house much colder. This is why the contractor suggested adding a new furnace and dividing the "New House" into zones. He stated that since some of the house is not used as much as other parts why heat them as much. Sorry for sounding ignorant but how do I calculate the heat load? If I don't need a second furnace and can just tap into the current furnace that would be fantastic!

Thanks for a detailed response! I have no experience with Heating and Cooling so any advice is greatly appreciated


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RE: How to heat new addition

The heat load is calculated by taking measurements of all windows, walls, floors, etc, and entering them into a software program. HVAC contractors should do this, but most don't. You can calculate for your own house by getting the homeowner's version of the software from the link below.

You probably have a duct work problem affecting some of the rooms in the house. It is unfortunate this was not addressed when the new furnace was installed 5 years ago.

Most general contractors are not very knowledgeable when it comes to HVAC. You need to do some homework and talk directly with a good HVAC contractor before you make any decisions.

Here is a link that might be useful: HVAC Calc


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