The question isn't whether you can improve the heating and cooling properties of the house. You clearly can. The question is how do you do so in the most cost effective way.

The #1 item is sealing up gaps. It doesn't much matter how many panes of glass you have if wind is blowing in around them. Same goes for doors, outlets, baseboards etc.

#2 is usually ceiling insulation. Sounds like that is taken care of already.

You can price out window replacement, but I think you'll find that it will take decades for you to recoup your costs. Storm windows are often much more cost effective.

For insulation, if you can't do outsides, then inside is the only option. You could put 2x stips on existing walls, insulate between, and then drywall over. Again, probably cost prohibitive and it would cost interior space.

You could also look at more efficient heating/cooling systems so they would be cheaper to operate even if you used them more.

When the windows are replaced I would make sure they're properly sealed so no gaps are there. Windows for the whole house (only a 920sqft house) are estimated to be $4000-5500, while storm windows wouldn't cost nearly that it wouldn't fix the unsightly windows now... right?

I'm new to owning a house and doing repairs so i'm not sure what 2x strips are? Is that like small versions of 2x4s?

The house currently has baseboard heating...

Thanks!

You can add rigid foam insulation on the inside of the walls for the highest R value and minimum loss of space.

If the plaster walls are in good shape I would seal it up and insulate the attic, add new windows and call it good.

Unless they have already been upgraded, the plumbing and electrical in a "1910 concrete masonry unit house" are liable to be pretty bad.

If you do not have a basement you will likely need to do most system work in the attic.
Wiring and plumbing can be dropped though cement block if it has not been filled for insulation.

The blocks will likely have a high Portland content and be VERY hard.
As in so hard a power driver will not put a pin into them.

Unless you are wiling to surface mount wiring on the walls (ugly as can be) you will need to drop lines from above (or feed up from below) and then recess boxes into the block.
It is not a job for the faint of heart (and can be a disaster if loose fill is in the blocks).

Thank you for the info. Plaster walls are OK but since the previous X owners didn't move water away from the house well there has been considerably more settling and cracked plaster but nothing that has cause major foundation issues. Luckily we receive only ~8" of precipitation a year here.

The attic is completely insulated as there was a new roof installed a few years ago. The plumbing is brand new and the electrical was updated in the late 70s/early 80s.

How hard is it to redo plaster walls? I might just go with new windows and redo the interior walls and like you said... call it good.

Can people drill holes into the concrete blocks and inject/blow foam into them?

furring out walls to add insulation is expensive.
and it will make problems for interior of windows
electrical and doors.

IMO better to invest in a blower door test to
pinpoint air leaks, and tighten the building's
envelope.
then check into 15-17 SEER hvac.
in my area heat pumps are very cost effecient.

windows don't provide the payback that they are
advertised to. about a 15% energy savings is the
true savings. air sealing and efficient hvac
can easily top that.

I've seen videos of foam being injected into
walls...but have doubts about how well it
actually works. I'd have to verify with blower
door and thermal scan.

both windows and insulation of walls are high
cost slow payback items. unless very cold climates.
windows can have solar screens..which work very
well at keeping the heat out of the house.

best of luck.

I had a 1929 home constructed from structural clay tile (SCT). So I know a little bit about what you're dealing with. The exterior walls were SCT with stucco/plaster applied directly to them on the inside and outside. The interior walls were traditional wood frame with lath and plaster. Any wiring or plumbing in the exterior walls had been channeled into the tile with the assist of a thick layer of plaster.

We found that there really wasn't a need for additional insulation. The hollow area within the tiles acted as insulation in and of itself. As mentioned above, the main culprits for leakage were windows and doors.

We did redo the kitchen and learned firsthand how difficult it was to deal with the SCT. Our solution was to build a wood frame wall against the exterior wall. We lost 4" of floor space and had to build out the trim on two windows, but it allowed us to run the wiring and plumbing that we needed.

Here is a link that might be useful:

"How hard is it to redo plaster walls?"

Very expensive if you can even find somone to perfrom the work.

Veneer plaster is common now.
A thin 91/16 to 1/8 thick) layer of plaster over blue-board (a special type of drywall).

Much less common is two coat plaster.
3/8 thick backer board is used as a base for a scratch coat of plaster and then a finish coat.

The assembly ends up around 1 inch thick and has about the same sound performance as a 3-coat (rough, scratch, finish) plaster wall on wood or expanded metal lathe.

If you are only doing outside walls and do not alter interior walls you will preserve the sound qualities withing the house, and likely improve the exterior wall sound qualities.

Every exterior door and window will require changes to the jambs and casings for the increased wall depth.

You might be able to find someone to inject into cement blocks, but it will need a low expanding foam and a lot of holes.

It may not even be worth the cost.

Every time I have looked at insulating plaster on brick exterior walls to add insulation the paybacks have stretched to over 20-30 years, even with estimates of increasing energy costs.

OP let me guess...you are a john prine fan?
or just like the 'don't cost very much
but it last a long time' lifestyle?

lol.

thanks for all the information! A lot of the rooms have added another layer of plaster or drywall to the CMU or plaster as the frames/molding for the doors/windows have little relief to them and basically blend in with the wall, I don't like this but if I'm putting in new windows anyways I suppose this can be fixed by adding space.

Many window replacements are done for no better reason than a strong sales pitch and government energy rebates. Nothing more useless than replacing century old double hung wood windows with cheap aluminum sliders and vinyl units that'll last maybe 20 years.

Tightening the structure--especially any above-grade portion of the basement--and upgrading the HVAC may be all you need for cost effective improved looks and comfort.

Whatever you do, DON'T REPLACE THE WINDOWS. Most new units fail within 7-10 years. Good windows may last 20. Restore your original windows and they'll last forever. Much of the energy is lost around the windows, and replacement windows are fit into the old frames. You then have no net gain. Add storm windows if the old ones are really bad, and that will give you plenty of time to restore them yourself, or you can hire someone to remove the sashes and restore them off-site. As the previous poster said, higher efficiency HVAC and programmable thermostats will do a tremendous amount for reducing heating costs. Always look for the best solution...even if it isn't the easiest, or cheapest up front. It may only cost $5000 to replace the windows now, but if you have to replace them again, and again, and again, restoration would've been far cheaper.

And, if you tear out the windows, you will be lowering your resale value by at least what you paid for the windows, if not more. Seriously.

windows..good low e argon gas filled windows with
non heat conducting frames..only save you 14%.
this is why they have been removed from rebate
programs.

a double paned window low e argon non heat conducting
frame will lower noise transfer. and reduce
condensation issues. but don't expect to save
a lot of money, but to spend a bundle!

best of luck.