HVAC recommendation for 3rd floor (attic) unit, poorly insulated

[Tyler Speelman]

I have a heat pump that needs to be replaced.

Residents currently have window AC units, but have complained that it is not cool enough ( rarely falls below 78 degrees on a hot day)

No complaints from residents when heat pump worked. 

Mitsubishi multi zone HP 24,000 BTU + 2 wall units install quote is $7,445.10, approximately $1,000 less for electric baseboard heat install. 

I am getting two other quotes from HVAC companies and have yet to hear back.

Would you do the less expensive electric baseboard heat with separate Central AC unit or go with the Mitsubishi mini-split for AC + heat or would you consider getting a quote for extra insulation (not sure if there is an easy way to blow it in)?

Any advice would be greatly appreciated. 

[Jim Hiler]

I would replace the heat pump unit and air handler (potentially adding a heat strip in it). If you already have the ductwork ran etc. a heat pump is the simplest way to heat and cool in a moderate climate in my opinion. If you're in an area that gets below zero a heat pump may not cut it. At which point you may want to add a heat strip in the air handler. If you opt for this just check with an electrician first because a heat strip can draw a lot of power 30 - 50 amps.

Check out this link to an article on Carrier's website.
https://www.carrier.com/residential/en/us/products/heat-pumps/heat-pumps-vs-air-conditioners/

Furthermore if you can find a local HVAC engineer or energy calc specialist to run energy calcs for you they can tell you exactly how many tons of heating and cooling you'll need based on the SF of the house, type of windows, type of construction (wall make up, floor make up, roofing etc.), how much insulation is currently installed etc. You can then have he/she run the calcs and plug in an upgraded type of insulation to say spray foam for example. That should reduce the amount the tons required to heat/cool space therefore reduce the cost of your system.

From my experience spray does a great job but it can be costly. It goes for approximately $2.50 - $3.00 per SF of roof in my area.