HVAC System for new addition

[idealtrucks]

I currently have around 1900sf with a 25 year old Trane Heat Pump. I will be building on an additional 575sf with a bedroom, bathroom, and closet.

I have got quotes for a new system for the entire house at roughly $$ and for a mini-split system for just the new addition for ~$.

What is going to be the best way to go on this, considering total cost (purchase price, and electric bill savings)?

[pecmsg]

Adding roughly 20% more Sq Ft of new tight construction shouldn’t need anything extra seeing how most systems are oversized anyway

[idealtrucks]

Current heat pump is only 3 ton.

[pecmsg]

A complete Manual J and D must be preformed to answer your question.

[rider77]

Current heat pump is only 3 ton.

Equipment isn’t sized to square footage.
Depending on how tight the addition is it could have very little impact on the conditioning needs of the space.

[kdean1]

Adding roughly 20% more Sq Ft of new tight construction shouldn’t need anything extra seeing how most systems are oversized anyway

Ditto.
Most systems have more than enough capacity for the house. The duct system is usually too small.
Do not assume you need a second system.

[BaldLoonie]

Only question is getting the right amount of air to the addition. And if it has a load/loss much different than the rest of the house, it may not be comfy. For example, south or west facing with a lot of windows, may need cooling when the main part doesn't.

A GOOD dealer can size the main house and addition and see how it would be to get appropriately sized ducts to the addition. Then you can decide.