You need to tell us the location or at least the country.

In the US you would need to insulate either the basement walls or the ceiling above regardless of the heating situation. The same goes for a crawl space.

Sorry, meant to add that I'm east coast Canada. The walls are insulated (ICF) & will have drywall covering for fire retardant.

HVAC says not to insulate the floor or the ductwork but to heat the basement.

Energy advisor says the opposite...don't heat the basement, but do insulate the floor and ductwork

Not a pro, but if it were me, I'd add the HVAC down there. You're giving yourself the flexibility of some day using it for additional space if you want. You could always close some of the vents part way if you don't want to waste heating / cooling money. Adding the HVAC now would be more cost effective than later.

Isn't this just a "tall conditioned crawl"? which seems to be the recommended thing lately anyway?

I view this more as "lightly conditioned" and I'd still insulate the ductwork.

Thanks @ Chicagoans...myself, I will never use this as living space & if the next owner decides to use it for living space, he'll have to at least dig down to install windows.

I just don't want to throw money away heating space unnecessarily or on the other side, waste money insulating where I don't need it

Thanks just_janni, yes, I suppose it's a tall crawl space....just wondering if it needs to be conditioned or the above floor insulated(?)

Thanks res2architect ...forgot to mention that I'll have some sort of dehumidifier system and that the energy advisor suggest that I may(?) just put a couple of electric floor rads in if necessary &/or if it got super cold for a couple of days

If the basement/tall crawl is part of the conditioned space--and it would seem to be as you have a furnace and whatever in it--you insulate the walls, not the ceiling, and you manage moisture.

Let Dr. Lstiburek explain, even though he's from Toronto.

I'll bite. the 8' crawl space is made from ICF blocks (R22 or more) but is the floor dirt or concrete and is there a moisture barrier and/or insulation under the concrete?

If it's concrete with insulation underneath the rational thing to do would add some heat below and save the money not insulating the floor. The "ENERGY" in the form of heat will rise to warm the floor and the majority of the heat you think is being wasted will actually be used above. The cost to insulate under the 1st floor to R40 will never be recouped from what little heat is transferred through the basement walls and floor, or at least your life time. With R22 walls, no windows, and an insulated slab the losses in your basement will be negligible.

If your 8' crawl space floor is dirt, or just concrete than insulate the ceiling and you'll have one heck of a nice root cellar. But you said you're going to sheet rock the crawl space which leads me to believe it's concrete with insulation underneath or the paper on the rock would rot, grow mold and maybe make you sick. This is another reason to condition below, or will there be air exchange between the outside to inside through vents? residential code (at least the USA) makes it clear that vents can be eliminated, as long as the crawl space is sealed and conditioned. The reason for vents, or a sealed and conditioned crawl space is to avoid rotting out the lumber and growing mold.

To summarize your adviser is wrong, and your HVAC guy is right. Condition the basement, crawlspace, secret bunker or what ever you want to call it.

Insulating to R40 on the floor would seem like wasted money. But if it is just a lot of batts, we aren't talking big money. Do you have a quote?

I suspect that your basement with a furnace and ductwork will essentially be heated. So you aren't really wasting much to heat it. Sometimes in situations like this, it really is the code that dictates what you do because common sense would say that the wall heat loss is very low. The basement will probably be over 65 naturally and certainly never below 50. So whether you officially heat it or not is almost inconsequential.

In the US, what I have seen is that ductwork is always insulated anyway. It is also leak tested for Energy Star even if the leak would all be conditioned space.

Start modeling numbers even if they are just models. The cost savings now on insulation should be easy.

Then model with wall sizes/slab and come up with heat loss - something a Manual J would do. And get a number. I suspect that number will be pretty freaking low. It won't be exact but it may give you some idea. You are probably looking at ground temps of 55. If you heat to 68, then look at the math.

In the end, it is all a math problem. The energy rater is probably pretty good at math. Can you ask to see his numbers or is he just quoting some rule?

One of the things the math depends on is what temperature you like the space at. If you heat to 72 vs 68, it makes quite the difference when you are looking at 55 degree outside wall temp - like 13 vs 17 which is like 30% difference.

I just checked with the contractor and he said that there's both vapour barrier & insulation under the concrete floor. Energy advisor said that painting the walls will be enough to protect the paper on drywall, but this sounds like, as Kevin pointed out, I may be getting into money I may not recoup in my lifetime. I will also need a dehumidifier system as it's very humid here in summer

He did mention perhaps just insulating 3 sides of the ductwork with the open 4th side to face the underfloor.

The reason I have this huge unused space is the number 1 regret of anyone I've ever spoken to with a crawlspace, was that they didn't go the extra 4ft

Still waiting to hear back from bldg code people. So, I'll check on batts costs as well as at 3000sqft, it may too be costly(?) and send to the energy advisor may so he can run the numbers.

Hi, CGKA,

The heating requirements for a well-insulated basement--even in coastal Canada--are pretty small compared with the above-grade living spaces. Your energy consultant should be able to run the calculations for you with a variety of insulation alternatives so you can make an informed decision. You'll also need to consider conditioning the space in whatever passes for summer in your locale. That means dehumidification--particularly if you'll be installing drywall (the paper facing is a wonderful food source for mold.)

Where I live insulation under the slab is now required by code, so that woudn't be a question, but it's also a good idea, The cost for a few sheets of rigid foam is pretty trivial in the context of building a house and it's really hard to retrofit later, while the benefit persists for as long as the house stands. I can't imagine not doing it.

Finally heard back from the building standards officer...he said that by code, I'm not required to heat the basement. Still waiting to hear back on the price to insulate the floor so I pass along to energy advisor to crunch numbers. Thanks everyone

Depending on where you are located in the country, it would seem plausible to heat the area during winter and hope that the heat carries through to the remainder of the house. Or take another heating initiative by insulating the floor as you suggested.

I would put a 6 or 10mil vapor barrier under the basement floor whether you heat it or not. Same with the garage floor.

FWIW - speaking as a home owner who knows nothing about all of this, compared to the experts here....

I have a house in New York. The walls of the basement are insulated. It is not heated and is not living space, but all the mechanicals are down there. The coldest it has ever gotten is the upper 50s, the majority of the winter it actually stays in the mid/upper 60s most of the time - merely from the heat given off by the boiler and perhaps the washer/drier.

The dehumidifier ran non-stop for quite some time after the build as all the concrete dried out. Now it generally only runs in the summer. To me, in your situation which appears similar to mine (as in I have no desire to use the basement as living space either!), I see keeping moisture under control as more necessary than adding heat.

No you do not need to heat. Your insulated walls and footings are below any frost danger. You may need to add air vents in the wall to outside air for a fresh air make up for your furnace and to remove excess moisture.

Your ductwork is probably insulated by design already. And if you're heating system is down there then the ductwork will help heat it.

Sounds like a well built home

I'm waiting to hear back from the building supply store (my guy has been off for a couple of days) regarding the R40 insulation costs for the basement ceiling/1st floor.,,, because, as David said, it might be more than it's worth since the basement is already so well insulated

Just heard back...not including labour, almost $7,500. Yikes! I'm thinking I could heat the basement for quite some time on that!

I also just relayed this to my energy advisor and he said that by dropping 2 or 3 ducts down & heating my basement to 15C-ish (59F) as recommended by the HVAC company, I will actually increase my energy score by a point or 2, but said it will come down to comfort as the floor won't be as warm. (he also reminded me to make sure that I can control the amount of heat that goes down so that I'm not heating it at the same temp as the living space)

He suggested I try it for a winter and see how it goes & that if I decide that I'd like to insulate, I could even go to as low as R14(?) to keep costs down and even that would make a difference.

So, for this first year at least, I'll go with heating the basement at a lower temp, not insulating the floor or painting the drywall, and see how it goes. I'll still need to install a dehumidifier as we have very humid summers here.

A vapor barrier under the floor slab will decrease your humidity levels.

outside air for a fresh air make up for your furnace and to remove excess moisture

Outside summer air brings in moisture. (Links are authoritative not advertising.)

Since the basement is evidently a conditioned space, make up air is in no shortage. If it is a condensing furnace, it will directly access exterior air.

- 3000sf, at 8' deep, is considered an "unvented tall crawl space"????

- 3000sf, is your unit(s) centrally located or off to one side????

- Energy consultant saying to add heat to "unvented tall crawl space" to raise temperature to 59dF, when a basement will naturally be from 60dF-65dF????

- Insulated ductwork in an "unvented tall crawl space" (flex standard, but sheetmetal?) that ranges from 60dF-65dF????

Hi 3onetree,

I'm not sure what the space is called...it was to be a 4ft crawl space, but anyone I've ever spoken to with a 4ft, wished they'd have gone the extra 4, so I did.

My HVAC company energy said to drop 2 or 3 ducts/vents for some heat to the basement...said not much, 15C-ish (59F) and no need to insulate the ceiling/floor (concrete floor is insulated & also has vapour barrier)

Energy advisor said absolutely no need to have heat ducts to basement but told me  I can always try it for next winter & if I don't like, I can always go back & insulate and that if R40 was too pricey, the go lower...anything would be a help. (said I may find the floors too cool as even 3°C lower temp will be felt on feet)

His recommendation was no heat & to insulate under floor/ceiling. 

As I'm waay over budget already, and the insulation will add to that, I think I'll go without this year and try it for 1 winter to see how it goes.

It was a good call to go 8 ft and I'd do the same but I'd use the space as a secret bunker to store my armory, gold, food and water. Along with power walls, manual power generator, ,control center for my network of satellites and stealth solar panels that look like bill boards. Can't forget the small security force of AI robotic soldiers but they don't eat much in standby.

Late to the party, but we had a basement under half our 1926 bungalow, opposite coast. Mechanics, an upright freezer, and storage only. We're more wet in winter than cold. Duct work for the heat pump we added was insulated. So was the basement ceiling. We had them put just one heat pump ceiling vent in the basement - I could manually open or close it. I mostly left it open just for reason of moving a bit of air - no Costco overflow or canned goods ever came close to freezing down there. However, if I didn't open it and before heating was changed, things stored in cabinets on the cement floor or even fabrics like occasionally used outdoor sport clothing could become musty or even show mildew spots. Just a little air moving solved that problem, no musty stored patio cushions, boxes of books or paperwork.