Heating an Unheated Basement (Help or Hurt Efficiency)

dbarberic · Heavy Crude Joined: Sep 27, 2005 Posts: 240

Currently at my two story house, my natural gas furnace only heats the first and second floor and no heat is directed into the basement (basement is unfinished). The basement is currently un-insulated other than around the rim-joist where the cinder block basement walls meet the sill plates of the first floor walls.

I did a large sealing project last year and plugged every hole I could find in the house and sealed all my exposed heating ducts. I did get a nice efficiency gain of about 20-25%, but my house still "feels" chilly when heated to 68F when occupied.

Do you think there would be any improvement in the comfort of the house and energy efficiency if I were to do install a vent where the heater could direct heat into the basement? I wonder if the cold, unheated basement is contributing to the general sense of chilly in the house.

As an alternative, what if I either insulated the basement cinderblock walls. Or, what If I insulated the bottom of the first floor (aka the basement ceiling) between each first floor joist?

Keep in mind the following:
-I do not want to do anything that will decrease my efficiency gains. Either keep it neutral or increase performance.
-My first floor is hard wood floors.
-When possible, I heat using my wood burining fireplace insert on the first floor (maybe this will change the recommendation). But I still heat roughly 50-75% of the time using my furance.

waldo · Tar Sands Joined: Dec 22, 2007 Posts: 44

I doubt you're losing much heat to the basement (heat goes up) but take a surface thermometer and check the temperature of your first level floor. (Or just feel it, is it very cold?) If its, like, 55 degrees, well that's cold and perhaps insulating the ceiling of the basement is a good idea. Keep in mind you need some heat flow into the basement; you don't want your pipes down there to freeze.

dsula · Heavy Crude Joined: Jun 13, 2007 Posts: 143

buyavowel · Coal Joined: Dec 31, 2007 Posts: 1

DBarb -

The short answer is that any heat you dump into your basement will be entirely wasted.

If you don't need to have your basement warmer than 55 degrees, then the best thing you can do right now to stop heat loss into the basement is to add insulation to the basement ceiling under the subfloor on which your hardwood floor is laid.

If you are going to be in the house for a long time, use polyurethane - it is the absolute best. You'll make up the money over crappy fiberglass over time.

The basement is the nosebleed of the house, and, after insulating your attic floor and your walls, preventing heat loss into the basement is huge.

You can buy kits to spray yourself at tiger foam, or you can hire a pro.

All you'd really need is 1 to 2 inches of polyU.

Here's a link discussing it further . . .

Hearth Discussion Forum

Pay attention to what Pope is saying - that guy is brilliant.

smallpoxgirl · Moderator Joined: Nov 08, 2004 Posts: 6339

Heating an uninsulated basement can be a huge energy loss. The walls are in contact with dirt that has a fairly constant 55 or so temperature year round. The bad news is that dirt has a tremendous heat capacity (much higher than the cold air outside your upstairs walls) and pretty much no matter how energy you pour into heating the basement, unheated walls and cement floors will stay 55 or so degrees. The good news is that is that it doesn't take a lot of insulation to be a big benefit, because the thermal gradient is only 13 degrees (68 minus 55) instead of the 60 or more degrees of gradient you could be facing with the upstairs walls and ceiling.

Clearly the easiest solution to your problem would be fiberglass insulation between the joists under the first floor. If you wanted to make the basement more inhabitable, you'd want to insulate the basement walls and floor. You'd probably end up with framed out walls and a framed floor with styrofoam sheet insulation between the studs and the joists. (Fiberglass in contact with concrete can tend to get wet and moldy.)
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katkinkate

I would insulate the basement ceiling and use it for cool storage of food and stuff.
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topcat

We have the exact same layout and heating methods. Last month, we had a new furnace installed and I asked the guy about heating the basement. His reply was that heat is not wasted as it rises to the first floor. But, after reading SPgirl's remarks I am taking a second thought (regarding the heat sink of the surrounding earth).

That being said, our basement remains around 58F, which is not bad for us. I have not insulated the floor joists since I think the insulation would make the basement slightly colder.
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dsula · Heavy Crude Joined: Jun 13, 2007 Posts: 143

Fiddlerdave · Heavy Crude Joined: Mar 18, 2007 Posts: 292

YEars ago, we installed a franklin stove in the living room of our old house. When we would use it, te living room became too warm, and the house had baseboard water heating, not central fan heat, so I couldn't turn on the furnace fan to distribute it.

So I installed a duct behind the stove, up about 6 feet and open at the top, that went through the floor and just opened to the basement. I put a small suirrel cage fan on the bottom and a switch. WHen we lit the fire, we turned on the fan and blew part of the hot air into the basement. The living room didn't get too hot anymore, but what was truly amazing the basement warmed up nicely, and the floors warmed up upstairs! Even a back bedroom that tended to feel cold started feeling much more comfortable in very cold weather, simply from a warm floor. This effect would persist for quite some time after the wood stove cooled off, and when we burned it every day for 6 hours or so, the effect was around the clock, and even for days without burning wood the basement and floors were warmer.

My next house that I can customize will definitely have an insulated outside wall basement, with some kind of heating (hopefully waste heat or solar) to keep the floors warm. It was wonderful! And it really only used the overheat from our stove with 7 feet of duct, 40 bucks including the fan.

Fiddlerdave · Heavy Crude Joined: Mar 18, 2007 Posts: 292

TreeFarmer · Heavy Crude Joined: Jun 26, 2007 Posts: 350

I just finished the insulating part of a basement project. This consisted of putting 4x8' sheets on 1" styrofoam insulation on my block basement walls. My walls are approximately 9' tall so I just started at the top and let the styrofoam hang down 8' and left the bottom 1' uninsulated.

I nailed the styrofoam to the plate at the top of the block wall and put in one line of adhesive about 3' down from the top.

This has made a noticeable difference in the temperature of my basement. The basement is still rather cool as I only inject a minimal amount of heat into it at this point.

Overall, I believe that you could thoroughly insulate your basement, pump in a little more heat thus making your first floor floor warmer and making your house more comfortable for very little additional cost.

Will it cost something? You bet it will. Will it lower your overall "efficiency"? Yes, more heat in the same size house means less efficiency if you calcualte efficiency like I do. However, you may find the cost of the extra heat to be more than made up by an increase in comfort.

EDIT!! Now that I think about it, this may not hurt your efficency at all. You are currently losing a lot of heat with uninsulated basement walls. Insulating them would reduce heat loss and thus would actually increase your efficiency.

Treefarmer

jedinvest

I think that insulating the underfloor of the first story is a good idea. When energy is limited, heating the smallest possible space is a good idea.

Next, insulating the walls will make the basement move livable (and, of course, help in efficiency category too). Be sure to leave at least one room or area uninsulated. It will make for a good wine closet or food storage (if the electrical grid is disconnected).

Lastly, this is one of my own projects that I did. I used 1/4 inch cork sheets on top of the unisulated concrete floor. Then I installed a low maintenance pergo-type floor on top of it. My tree-hugging friends say it's artificial. But it is much more livable than wood floors even since it is harder than wood, water resistant, stain resistant, and warmer (due to the cork underlayment) and softer at the same time since it gives but doesn't get dented.

SpringCreekFarm · Intermediate Crude Joined: Mar 03, 2006 Posts: 930

I notice you mentioned that you burn wood in a fireplace insert. Have you considered putting a woodstove in your basement and heating the house from the underground up?

Here's mine:

My unfinished basement regulates the temperature fairly constantly as the stove heat fluctuates between fillings. If the fire goes out, my house stays warm for an additional 24 hours or so if I'm not home to start a fire. The fire burns for most of the winter as I don't let it go out too often.

This stove is all I've heated my house with for the last 5 years or so since I put the insulated chimney in. I do have an oil furnace further back behind where I'm taking the picture from, but it only serves as an air circulation device.

If you could get a way to circulate the air up to your other floors, I think a basement stove would help heat the house nicely.

Just my 2¢.

jedinvest

Actually, it was 1/8 inch cork sheeting on top of 6 mil polyethylene vapor barrier, I think.