Cost of Adding HVAC in attic of old house?

[Anonymous]

We have a 1953 colonial, maybe around 2100 sq feet with one HVAC system. The upstairs gets so hot in summer so it’s been recommended to get an additional HVAC system in attic. Any estimate on cost for that? If you’ve done it, did it work to help cool the 2nd floor?

[Anonymous]

Cheapest and easiest is a window AC unit. I bought one for about $150 and put it in myself. Can't remember how much it weighed.

[Anonymous]

I think you're issue will be that your ductwork is probably not good at this point so you will need to both add a new system and replace all of the ductwork to do it properly.

Are there particular rooms upstairs that aren't heated well or is it several?

Look at ductless options or get ready to tear open the walls and get two units to do dual zone.

[Anonymous]

Get a mini split like from Mitsubishi.

[Anonymous]

Look into a mini-split for that specific situation.

[Anonymous]

I was quoted $4500 for a mini split in 2020, so probably $5000-5500 now.

[Anonymous]

Mini-split was about $5k installed in our attic (that's probably the higher end, you can buy the unit and have a handyman install)

[Anonymous]

Anonymous wrote:I think you're issue will be that your ductwork is probably not good at this point so you will need to both add a new system and replace all of the ductwork to do it properly.

Are there particular rooms upstairs that aren't heated well or is it several?

Look at ductless options or get ready to tear open the walls and get two units to do dual zone.

It’s really just the whole upstairs-which is 3 small bedrooms and 2 small bathrooms, no real landing or anything. It’s small.

[Anonymous]

Typically in houses of that vintage the attic is outside the conditioned space. There is a layer of insulation between the attic and the second floor, and the attic has vents which make it exposed to outside air.

If so, that's not a good place to put your HVAC equipment. It's hot in the summer, which makes the equipment work harder, and in the winter it can be below freezing. If there's any water in the system -- like in a condensate drain -- it can be damaged when it freezes. Some codes will allow HVAC in an unconditioned attic, some won't, but it's not a good practice, you want the HVAC in conditioned space.

One thing about attics like that is they're often poorly insulated, and they're pretty much the easiest part of the house to add more insulation too. I would recommend doing that first. A thing to look out for is making sure the insulation guy doesn't cover the vents in the attic, that will lead to moisture building up which can rot your roof from the inside.

[Anonymous]

As someone who is going through this, I would have an electrician check out your wiring, panel and service line first.

We found out that we had insufficient service to add mini splits or heat pumps to cool our upstairs, so we had the fun of upgrading that with our utility provider, redoing the panel, and then getting to rewire half the house where seemingly new wiring was actually running off knob and tube from 1937.

[Anonymous]

We have an old Cape Cod with bedrooms on the second floor. We have a unit just for the second floor that is a godsend. It is ducted in the attic and has vents into the bedrooms and bathroom. It's no big deal to have it up there, it just has to be accessible for installation and repair. Make sure you get one that is variable speed to pull humidity out.

Our upstairs also has very poor insulation, so it gets hot even on days when it's only about 80 outside if it's sunny. On milder days that are common in this area, the upstairs one will run to keep the 2nd floor cool but the main floor one won't run at all.

[Anonymous]

small attic just get a window ac.

[Anonymous]

OP—got the quote. Around $20K for adding HVAC and creating ducts to go into each bedroom and returns. Wasn’t looking to spend that much. For the mini-splits, would it only work for one room or could it potentially cool the entire small upstairs a bit more?

[Anonymous]

Anonymous wrote:As someone who is going through this, I would have an electrician check out your wiring, panel and service line first.

We found out that we had insufficient service to add mini splits or heat pumps to cool our upstairs, so we had the fun of upgrading that with our utility provider, redoing the panel, and then getting to rewire half the house where seemingly new wiring was actually running off knob and tube from 1937.

A 1950s house is very unlikely to have the unsafe knob-and-tube wiring, but is likely to need an electrical service upgrade and panel upgrade to support the new A/C. Probably start with checking into that.

[Anonymous]

A mini-split often works well in OP's situation. That likely is lowest cost option. Not all HVAC companies are equally trained on mini-split installation, so shop around.

If there is existing viable upstairs forced air ductwork, then one would need to detach that from the downstairs zone and close off the connection thoroughly. In that case, I would pay to have all the upstairs/attic ducts resealed with aluminum tape (not duct tape) at every seam to minimize cold air loss to an unconditioned attic.

Because the house is so old, the roof planks likely are bone dry. That means another option would be to close off the attic (i.e., no vents) and have spray foam insulation put under the roof planks and along the eaves, also removing any insulation from the attic floor. This makes the attic conditioned space. We did that and it was a huge reduction in both heating and cooling costs. It also meant a conventional heat pump blower unit could be put in the attic of our 1963 colonial.