[logan176]

I am trying to figure out my options for heating my basement once it has been finished this coming summer.

I have a Cape Cod style home built in 1951. I live in southern NewYork, climate zone 5. The foundation is made from concrete block. When the renovation gets under way, I am either going to be insulating with 2" pink foam board or R13 batt. The finished basement will add 500 square feet to the living space.

I have a high-efficiency natural gas furnace that was sized for my entire house, including the basement. However, I am already running two floors with one zone. The system is very well balanced with there only being a two degree difference between the first and second floors no matter the season.

I do not want to add a third floor to the one zone I currently have. Putting downstairs on its own zone is going to require running a lot of new duct work and will double the size of the bulkhead around the main trunk. My ceiling is only 6' 10" to begin with.

My HVAC guy recommended installing a Mitsubishi ductless heat pump that will both heat and cool the space. I'm not concerned with AC because the basement has always been cool in the summer. I was told that with the Mitsubishi unit running during the summer, I can stop using the dehumidifier.

Another option I was considering was to use two plugin space heaters. As is, the basement stays fairly warm. Right now it is 32 degrees outside and my basement is 61 degrees. The thermostat on the main floor is set to 68. When temperatures have dipped to 0 degrees, I think the basement has gone as low as 55. I know insulating the basement will warm it up even more, but when the duct work is covered with sheetrock, less warm air will be leaking into the space.

My sister picked up a couple electric baseboards with oil in them for her house. I've read that electric baseboards can use up a lot of electricity. I'm not sure if the ones with oil are that much better.

My family and I plan on being in this house for a long time. I have already gutted the rest of it to the studs and put it back together. I'd like for my solution to be as energy efficient as possible, within reason. I don't mind spending a little bit more money on a project as long as the job is done right.

I would love to hear everyone's ideas. If need be, I can upload photos.

[ballengerb1]

You have many issues to consider.If you basement is block there is likely some moisture getting through the walls so cover the walls with visqueen and then batts or use the foam board. Your hvac guys should be able to install a cold air return and a heated forced air supply to the basement. The supply vent can be opened and closed with seasonal changes but the cold return will be open year round, a good thing. The Mitsubishi units are good but drink power, space heaters are not a long term safe option and they use more juice than you might think. You are basically going to have a 3 story house with HVAC in the lower floor. Your existing furnace should do the trick.

[logan176]

I thought the plastic vapor barrier is supposed to attach to the studs after the batts are installed. So, if I'm reading your directions correctly, you're saying I should use visqueen between the batt insulation and the block, but I don't need the visqueen if I go with the foam board.Now for the furnace. If I heat all three floors with the same unit, should I put the basement on it's own zone? If so, I know I will need a new supply trunk, but will I also need an additional return trunk or can I tap off the existing return trunk?Also, if I close the supply vents but keep the return vents open, won't that throw off the system's balance? Or will the lack of new air slow down the amount of return air pulled from the basement?Thanks.

[ballengerb1]

Your thoughts about the vapor barrier are correct for the main and second floor but not the basement. First and second story the moisture is on the inside of the living space from cooking, washing and people. You want to stop that moisture from getting into the insulation. In the basement it's coming through the block from the soil. That's why you need that Dehumidifier. Visqueen on the block wall, then unfazed batts. If you drywall I'd recommend green board or blue board, mildew proof if your wallet can handle it. As for the current furnace I believe you said it was sized for the whole house including the basement. Close able supply vents on all 3 floors would allow you to zone the manually. I only have to open/ close vents twice per year. In the winter open the basement supply and close the second floor. The heat will rise. In the summer open the second floor and close the basement. Return air vents are nor closeable. I also recommend setting the fan on your stat to ON rather than AUTO. It only only increase your electric bill a slight amount, the fan uses most of its electricity starting up. Once the fan reaches full speed power consumption drops dramatically.

[logan176]

I'm already used to keeping the fan going all the time. That's how I'm able to keep the two floors within two degrees of each other. Now I understand what you mean by closing the vents. So it sounds like you're saying to keep all three floors as one zone?

[ballengerb1]

That depends on how much money you want yo put into this project. Multiple zones simply use automatic dampers and multiple thermostats. You can accomplish most of that by opening and closing vents.

[logan176]

Gotcha. If I was to go with two zones, would there wind up being issues with pressure during those times when only the basement zone is in use? As of right now, the furnace pumps out heat to 7 registers. If I put the basement on its own zone, that seems like it would be a lot of air moving through 3-4 vents. Would I need a bypass damper?

Speaking of vents, how many registers do you think I would need for 500 sqft? I will be using 6" round ducts and one main return vent installed on the wall closest to the furnace. I will also insulate the walls with the 2" pink foam boards. As of right now, with no supply vents, no return vents, no insulation, and drafty old hopper windows, the basement reads 60 degrees when it's 32 degrees outside.

[logan176]

Barring any complications, I've decided to add one duct run with 3-4 registers, one main return, and a manual supply damper for the basement. If I don't like the manual damper, my utility room is large enough that the second zone with electric damper can always be added on later.

I just finished speaking to my building inspector and he said I'll need R13 insulation for the basement. So, that kind of eliminates the rigid foam unless I want to put two layers of foam or put fiberglass on top of the foam. A contractor who came over this morning to give me a quote on the sheetrocking and taping mentioned visqueen, but he also mentioned using paper-faced batt insulation as long as the fiberglass doesn't come in contact with the block foundation. He said the gap will help to evaporate any moisture that seeps through the block.

Is paper-faced fiberglass a viable option if I leave a half inch or a whole inch of space between the fiberglass and the foundation wall?

[logan176]

So, it’s been a while and the basement renovation is still underway. I decided to go with 1” XPS foam board against the foundation wall along with R16 Roxul batts. I also took your advice and tapped into my furnace for heat.

The basement will be 675 square feet with 7’ ceilings. The supply duct has two 6x10 registers. This should be enough because the basement is usually only 10 degrees colder than the rest of the house in the middle of winter.

The next thing I'm trying to figure out is the return duct. I plan on tapping into the main trunk in the utility room. From there, I’ll use an open bay in the wall to bring the return vent about 6” from the floor. Will a 6” round duct pull enough air from the room or should I go with an 8” duct when I tap into the return trunk?

[joypulv]

Interesting to me, the whole saga (except for the heating, which I don't know enough about).

I'll be curious to hear how the insulation will work out over years. My experience and reading has shown many failures with basements regarding any materials at all against the basement walls, depending on several factors OUTSIDE --- the amount of ground water and the type of waterproofing ---- and age of the block or poured concrete. In my parents' house, it resulted in millions (seemed like millions) of bugs, even though they were harmless pillbugs.

The slab floor was another problem in itself.

[logan176]

As a follow-up to my last question about the return duct diameter, the basement supply duct taps to the furnace with a 6” connection.