Leaning towards heat pump

Ah. Well, I stand corrected by superior knowledge and understanding of thermodynamics. Thank you.

"Can't see the forest but for the trees."

Ya'll are running around in circles. Ask yourself, do you want your basement warm or cold?

If you want it warm insulate it well and make it part of the house, because the r-value of your typical uninsulated foundation is abysmal. And you are seriously losing more heat there than your attic if you have even a couple inches of insulation up there. Everyone concentrates on the attic but as Jamie pointed out radiation goes in all directions equally. Only the stack effect and the temperature gradient it creates causes more heat to be lost upstairs and good air sealing with even a little bit of insulation is enough to tip the scales back down to the basement.

If you don't want a warm basement, insulate the basement ceiling and completely exclude it from the house but then any heat from the mechanicals will be essentially lost. Even a small amount of insulation in the basement ceiling will ensure almost all of that heat from mechanicals goes into the ground or space and never makes it to the house. You will decrease energy consumption of the structure overall because of a smaller surface area exposed but will paradoxically reduce the efficiency of the heating equipment. Also have fun air sealing around every penetration for every wire, pipe and the basement door.

If you have any kind of mechanicals in the basement insulating it is the only sane option.

If there is nothing in the basement and it has no value to you as storage than excluding it is the sane option.

All these other arguments about the equipment helping to heat the house are missing point.

You could always wrap the pipes in heat tape and insulate them. Or just move them up into the joist bays closer to the subfloor and insulate the joist bay. The energy use to keep those pipes unfrozen would be minimal compared to the energy used to heat an entire uninsulated basement.

The reason there's a gradient is because dirt does have an R value.
So does snow for that matter.

It's my personal opinion a house should have a basement, and that basement should at least be partially heated. 50-60F is fine, and it sounds like that realistically results in fairly low heat loss.

Perhaps that's why my dad's basement that just has a 94% direct vent furnace and duct board in it stays around 50-55.

But like I said, I never saw any of the field stone in my foundation sweat even when it was -8F outside. Not even the exposed areas above dirt. I'm guessing part of that is due to mass, but it apparently does have some R value to it.

Something to look at and ponder: This is my house before I insulated the basement walls.

But the moment you insulate the foundation that calculus changes.

Myself. But I don't go around asking people if they have insulated their basement and I'm not really in the trades, so no, I can't. But any house built with in the last decade should have some amount of basement insulation however if built to code.

As for retrofitting, i think thats more to do with ignorance.

Its not a lot of material or funds? Say you have a square house 24x24 with a 8ft deep basement. It would take 24 sheets of whatever foamboard insulation you choose. If its polyiso that works out to about $1200 before tax. Im including the price because it is right off menards website so not exactly region or a trade secret.

Now polyiso needs an ignition barrier such as drywall. So 52 1x3 furring strips $115. 24 sheets of 1/2" basement board 318$. Of course misc stuff such as drywall screws, mud, tape, tapcons for furing strips, sprayfoam for the joints in the insulation. And your time.

Granted this will not work for all basements. Stone basement? Notta chance. Water pouring in? Nope. Mid century basement with concrete block in good condition? Almost certainly.

For $2k one could go from a cold, damp basement to something that is much easier to heat and keep dry. Run a dehumidifier all summer long? This could pay for its self from that alone.

The easiest way to put a number on it is to use a heat loss calculator and punching in the specs of the foundation both with the basement being insulated and uninsulated and look at the difference. I did some years back and the math is what informed me to tackle my basement before the walls or attic in my house. I had always assumed the basement wasn't a large loss because hey its in the ground. Then I ran the numbers and did not get the results I expected. I don't remember the exact numbers but it was eye opening I remember that. About as eye opening as how ineffective replacement windows are vs good low-e triple track storms over original wood windows. Clue: replacement vinyl windows often have a negative ROI, storm windows have a very favorable positive ROI.

Works… if the walls are reasonably flat. If they are 200 plus year old fieldstone… not so much.

I also want to point out that the stick wall is uninsulated except for 1/4" foam board under the vinyl. So 3/4" thick sheetplaster, 2x4, 3/4" "shiplap" sheathing, old cedarshakes, 1/4" styrofoam crap, and finally vinyl siding is the construction of the wall. Maybe r4 or 5 when everything is taken into account. Pump it full of cellulose or that foam usa insulation uses and it would be a noticably larger temperature difference I bet.

Edit: actually there is blown fiberglass up by the second story hall window directly above the door. The attic was insulated some time in the past and they also blew it down through the balloon framed walls as far as it would go. Balloon framing was used from the second floor up to the peak of the roof in the attic on the gable ends. So that 34.2f vs 30f surface temperature might be the difference from no insulation to a fiberglass insulated stick framed wall.

If you're going where i believe you are, no I'm not too concerned about moisture wicking up into the sill plate. There is sufficient distance between the top of the foundation and grade to keep it dry. It is something I will keep an eye on. If need be I could always dig down and seal the foundation. Which might need to be done at some point anyways. I have no intention of jacking up the house to install a capillary break between the two. I'd rather dig a trench.

But to answer your question the sill plate sits directly on the foundation and I used canned spray foam to seal the joint between the sill, foundation and polyiso. Eventually when I have a few other projects done that are out of the way I'm going to buy one of those kits and spray foam the rim joists all the way around the house from the subfloor to the sill and polyiso.

Basically the terracotta block foundation has been moved outside of the envelope of the structure. The polyiso becomes the edge. The only consideration is how much moisture can get to the sill, and potentially frost freeze cycles since the foundation can now get much colder. But how is this any different than say an unheated garage?

I don't see what you are getting at. If someone has a steam boiler with large standby losses they have only a few options to address the losses.

Rip out the entire steam system and replace it($$$$$)

insulate the basement and bring it into the envelope($$$$)

or just live with the loss.($$$$)

Which one is the most cost effective?

Insulating the basement will absolutely reduce the heat lost through the foundation. To suggest otherwise goes against the laws of physics. It just comes down to the question of if that alone will have a reasonable ROI. Over the life of the boiler maybe not, over the life of the structure absolutely. But to calculate just how quickly it pays for it's self you need to account for all of the variables. Not just cherry pick the boiler.

This app is pretty limited, but I'm not getting on the desktop and playing around with the software on that for this debate.

I got a bit different numbers than yours

A simple 24x24x7' box. No windows no doors ceiling factor is 0 because it is at or above the basement temp, uninsulated concrete slab. For the wall it does have an option for a partial above grade block foundation. Just changing what I believe is the u factor from a partially below/above grade bare block wall to something resembling an insulated wall saves 5000btu an hour at 30f outside and 60f inside. My only complaint is that it is saying that bare block wall is over 3r on its own which I question. But since we're comparing the same walls just with more insulation the savings should correlate regardless. In reality due to infiltration, windows, atleast one door and probably multiple flues or atleast multiple appliances going into a single flue the heat loss in a typical basement is going to be much higher even with just a 30f delta. Now lets drop the outside temp around this very simple box to 7f. 12873btuh uninsulated vs 4340btuh insulated.

Now lets look at our typical 2x oversized boiler: 100 year old home that realistically uses about 60k btuh at design but has a boiler that can do more then 2x that. The difference between its IBR and DOE rating is 18000btuh. With the amount of heat that boiler puts out that basement might stay well above 60f. Something I personally experienced last winter. Mine stayed in the 70's, in fact it felt more comfortable in the basement then upstairs even with the temperatures being comparable, especially the dinning room with it's wall of windows.

Ill agree in a perfect world where everything was sized right, standby losses should be minimized. But we don't live in a perfect world. Most heating systems are grossly oversized. Most of these people are not going to replace their heating systems until it dies. Guess what? Most of these people will hire the lowest bid and will probably be sold to much boiler or furnace again as well.

I have some questions:

You have a single "wall factor". This wall factor is not identical for the wall in contact with the dirt versus the wall in contact with the air. This tends to invalidate the comparison as the wall in contact with the air is where most of the loss occurs.

You have a "floor factor" of .81 with an indoor temp of 60F and an outdoor temp of 30F. This is clearly incorrect as the "outdoor temp" of the floor is the temperature of the dirt below the floor…………estimated at 50F.

I would argue depending on the insulation of the rest of the house the loses to the basement will be much greater than 10%. Add just a few inches of loose fill fiberglass to the attic and suddenly you'll lose more btu's to the ground then to the attic. It's one of the reasons the code is now mandating continuous insulation as a percentage or all of it. Sure you might be r20 or more on a 2x6 wall but that relatively small surface area of the framing becomes the dominant loss. Likewise you could have r60 ceilings and r30 walls but if the basement is cold you're going to lose everything there. And with 2x10 joists you could shove r30 between them but you still have upwards of 20% of the surface area at whatever the value is per inch of that wood.

Now since so many are convinced insulating the floor is the best option lets pan that out. 500$ for the fiberglass to do that scenario. And since you insisted including labor costs for the polyiso on the foundation, a job any competent homeowner can do themselves, include it here as well. And make sure to include the cost of air sealing every penetration going into the subfloor, and insulating around the basement door and the stairwell as well, which at the very least is going to include drilling into finished walls and patching.

It is much more difficult to get a good seal on irregular surfaces with lots of penetrations such as a ceiling or attic floor especially one that has an entire stairwell going through it. It is why CI at the envelope boundary performs so more better that fluffy stuff shoved in a framing cavity. Will the saving of the boiler pay for it all? yes. When? Maybe in 10 years maybe 100, it depends. But that is far drom the only benefit.

One other point I want to make is we're using a simple 24x24 box as the example. What happens when the box gets larger. Much larger. The surface area of the foundation with 7ft ceilings is 672sq ft, the surface area of the ceiling is 576sq ft. A 36x36' box is 1296 for the ceiling, but the foundation is now only 1008sq ft. ;). See how the math is starting to tilt the other way?