Mini Split Condenser Sizing

rather_be_sailing

I am looking at buying a mini split system at a home demolition auction. Would hire a local licensed contractor to remove the unit and set up at my house.

Model is Mitsubishi MXZ-8C48NAHZ, with hyper heating. The auction also comes with three units, two 12k and one 9k. I imagine it also has a branch box.

I have a living room of 900 sf and two bedrooms each about 250 sf. My home is in the Northeast, with temps down to about 5 degrees at worst. Specs say this unit handles 32,400 at 5 degrees. I want to use this as primary heat source (will keep baseboards as back-up.) I am not big on using A/C, but will use it a bit, and would like humidity control. I might add another room in the the next 5-10 years.

I have gotten estimates from contractors and most recommend a 3-ton condenser, so I understand this unit is overpowered for my needs (although clearly the current owner wasn't bothered by that.) And I also understand cassettes should not be oversized for the rooms, and I may be better off purchasing a second 9k for a bedroom and 15k for living room. I also understand there will be lines and everything else needed to set the system up.

But would purchasing this large condenser present issues? Thanks.

SuperTech

Yes it could potentially present issues. No one can tell from here what size system you need. A manual J load calculation needs to be performed to determine equipment sizing. A lot more than the size of the rooms and where you are located is factored in.

I wouldn't recommend buying a used system from an auction. You have no idea what kind of abuse and neglect it has been through. Maybe the original installer never used a vacuum pump when he installed it and the oil in the compressor is contaminated with moisture? Maybe the compressor or inverter board is shot?

I know it's tempting to try to save money on things but a bad decision like this will usually lead any "savings" being negated by expensive repairs or replacement of the equipment. Buy something new, professionally installed that comes with a good warranty. You will probably be happier with the results in the end.

pecmsg

Yes!

Oversized minis have very poor dehumidification in cooling. A WAG 1000 Sq ft in the NE needs a 9000 -15000 BTU's.

Something that complicated, without and history of who installed it or haw is asking for trouble.

Have you called around and gotten quotes for removing from the old structure, moving it and reinstalling it?

rather_be_sailing

Thanks for your response. I do understand the risk of buying used equipment. The unit is coming from a multi-million dollar house with top-of-the-line appliances, so I am guessing it was well maintained. And right now there are no bids (undoubtedly for all the very good reasons you gave.) So it is very little financial risk.

Other licensed HVAC contractors, who have inspected my house, have recommended two 9k units for the bedrooms, and 15k for the living room. So these are not my uneducated guesses.

Appreciate your help.

ChrisJ

The amount of cooling or heating required depends on a lot of things including how the house is built and your preferences on temperature.

I have a 1600sqft house in the NE and 3 tons is barely enough. It works fine but it's by no means oversized.

But I like to keep my house 72 during the day and 68-69 at night and insulation isn't the houses strong point.

My opinion on the situation is if I was paying a contractor I'd never consider used equipment. I'd want him to give me some recommendations on what equipment he wants to use.

rather_be_sailing

Thanks. appreciate your help.