What'st he best way for me to setup heating in my basement without getting a feedback loop of thermostats?

January 22, 2005 10:02 PM

Our 1200 sq. ft. partially finished basement is cold. There is insulation in the ceiling, and the windows are pretty new. Our thermostat is upstairs, so when the upstairs is comfortable, the basement is about 5-10 degrees cooler (a guess), even though there are heating vents in each room.

Can I just hook up a squirrel fan and pump warm air from the ground floor downstairs? Cut more vents in the ducts? Any other possible cheap/simple solutions?

I get the gnawing feeling that I'm stepping into a complex feedback loop problem--if I install a second thermostat, then the two thermostats duke it out until one of them wins or becomes skynet. Bonus points if you can point me to a place online where I can ask these questions and not get my head ripped off by HVAC professionals.
posted by mecran01 to Home & Garden (15 answers total)

I'm not cold weather or basement expert but I remember when I was a kid and lived in Washington state briefly, we had baseboard heaters in the basement. Those things could be controlled by their own thermostat.
posted by birdherder at 10:12 PM on January 22, 2005

I but a seperate duct from my basement (floor level) to my first floor (ceiling level) with a small variable speed fan forcing the cold air up. I vary the speed as needed.

I did lose a small portion of the back of a deep closet.
posted by page404 at 10:36 PM on January 22, 2005

Put in more insulation.
posted by slipperywhenwet at 11:09 PM on January 22, 2005

If your basement is that much colder I'd have to guess that it isn't insulated correctly. You may want to have a look at how the insulation is laid at the ground floor level - it sounds like you have cold air coming in directly between the basement ceiling and the ground floor. Also see what kind of insulation has been done around the walls.
posted by Dipsomaniac at 11:17 PM on January 22, 2005

Cutting more vents seems like a losing proposition. The fact that the split is equally divided is probably more important. You might be able to get something similar to a blast gate for the upstairs heating, and close it partially, to compensate for the difference. This feels like an inefficient but workable solution.

If you use a fan, you're going to have to deal with the noise, with either a quiet (pricier) fan, or insulation.

I have no HVAC degree and no nothing from insulation.
posted by Jack Karaoke at 11:20 PM on January 22, 2005

know nothin from insulation, arg..
posted by Jack Karaoke at 11:21 PM on January 22, 2005

(Oy. Please don't make many short paragraphs like that.)

You probably shouldn't try to heat your basement with warm air from your upstairs residential spaces. Most people don't know this but generally the furnace and ductwork are sized to the amount of space that is supposed to be heated; if you start heating a big new space such as a basement that is poorly insulated, you are going to drastically shorten the service life of your furnace.

Basements DO tend to be cooler, because the cold earth bleeds away heat through the concrete. When you finish out a basement nowadays, the basement wall will be covered with a veneer-type wall including studs and insulation (typically foam panels). Short of that (and especially if the basement is already finished but poorly insulated) you'll have to make sure that there are as few leaks as possible in other areas. Look at recaulking along the sole plate of your exterior walls, for instance; weatherstrip basement windows, perhaps add storms or at least a plastic covering. (All best done in better weather, alas.)

And yes, the HVAC pros seem to be one of the prickliest bunch I've ever seen, anywhere (especially on alt.hvac, which has a reputation; if you go in there unawares ...)

Get a book like New Complete Do It Yourself Manual which has great illustrated tutorials on these sorts of topics.
posted by dhartung at 1:13 AM on January 23, 2005

Mecran01, a few questions:

1. What exactly do you mean by "partially finished basement"? What is the basement composed of?
2. What is warming the air for your system?
3. Do you have a thermometer to measure the actual difference in temperature? (darthung typical basement analysis might point to one situation which is the comfort of the space based on what the occupant "feels": e.g. "this floor is cold".)
4. Is the basement open to the rest of the house? Doors left open? Anything like that?

I'm not a HVAC contractor or "mechanical" engineer but as an architect I need to at least have a sense for the solutions you seek. Doing it from afar is difficult -- hence the questions. If your case drops off the front page feel free to email me.

In short, the problem is that you have two heating zones: at least one area of your home has different heating needs than the other. This is actually the same for your entire home and the heating/cooling system should be (should have been) balanced to reflect that. This is why cutting more holes in duct-work is not a solution: the duct has been sized to bring a certain amount of warm air -- cutting a second hole does not increase that capacity.

Improving the insulation as already suggested will help because it reduces the heat "called for" by the basement zone. Closing vents upstairs (don't need a blast gate :-); your grilles might have operable dampers or you can insert appropriate bits of cardboard) will also balance the system: this works because the thermostat will keep calling for heat upstairs as you supply less there, thereby increasing the overall supply to the basement. Your system will run longer as a result. Sounds inefficient but you are still then doing what needs to be done: add heat to the basement. Your heat source is likely many times more efficient than any supplemental heat you can add to the basement.

That too was suggested above: add supplemental heat to the basement. This can be accomplished with something that is tied into your existing system: a second thermostat and controller at a minimum. This works because the system will get two different "calls" for heat. Sometimes these calls will overlap, sometimes not. You can also add something independent: i.e. a space heater. It should have a thermostat. The front-end cost is quite low but depending on the demand for heat, the end cost for a space heater can be quite high.

If you are looking for an integrated, long term solution you will need to find a local home improvement/HVAC contractor. Things might seem like a fleecing but truth be told they really are not -- everyone is out there trying to make a living. The fleecing part comes when you pay for solution that is poorly considered or simply does not work. Even the best efforts on problems like this can make mistakes.

The best person for a job like this will be an HVAC contractor that also does minor home improvements. I have used one in Cambridge, MA before but I don't think they will work in your area. Check around -- talk to folks. Get estimates and a feel for them when they study your problem in their site visit. Your instinct might be good enough to see that the person knows what they are talking about although even I, with years of construction experience, have been way off the mark on that score. It's people!

Oh yeah, and your fan solution? That might work as it removes some of the supply being called for on the story above to supplement the inadequate supply below. Then again, hot air rises so you will need to keep that wamr air that you moved into the basement down there.

Damn! That was a wordy answer!
posted by Dick Paris at 4:08 AM on January 23, 2005

After posting that, I thought of what my father would say: "Put on a sweater."
posted by Dick Paris at 4:10 AM on January 23, 2005

Oh, and cutting another vent in a duct can be a solution but only if the existing vents are undersized for the volume of air being pushed through the duct. I don't know all of the proper science behind it but, aside from doing the math, excessive air noise at an existing vent might indicate that additional or larger grilles are called for. Make that a big might though.
posted by Dick Paris at 4:18 AM on January 23, 2005

Two thermostats shouldn't be a problem as long as you don't have one set to heat and the other set to cool. Also, I second Dick Paris' suggestion for damping the air flow upstairs. It didn't completely solve our problem (we still need to use an electric heater in the basement occasionally), but it did help quite a bit. Our grillles came with adjustable dampers, and there were also rotatable metal plates installed directly below each grille in the ducts.
posted by Krrrlson at 8:06 AM on January 23, 2005

The ducts running from the furnace to the rooms upstairs should have valves in them. Usually a circle of sheetmetal inside the duct, near the furnace. There's a small handle on the outside; with the handle pointing down the length of the duct, it's open, pointing across, it's shut.. If you angle it, it blocks part or all of the airflow. Or you can partially shut the grates in the upstairs rooms.

So keep the basement ducts open all the way, and partially shut the upstairs ones, sending more heat to the basement. This works for a too cold or too room, too.
posted by jjj606 at 8:25 AM on January 23, 2005

Response by poster: Thank you for the excellent information and advice. This looks like a very solvable problem at this point and I'm grateful.

On relatively warm days like today (32 degrees) there is a 6-8 degree difference between the basement and the first floor. Additional factors: One room is drywalled. The others have bare cement with framing and carpet on the floor. The ceiling is insulated but not sure what the r-factor is. There is a cold storage space that is uninsulated but sealed with a door. That will get insulated next.

We also have an oxygen intake for the furnace that leads to the outside. One can feel the cold air blowing in through that. I will also put 3 mil plastic over the windows, which are primarily for light, not for viewing the window wells, and get some magnetic vent seals for some of the rooms upstairs, such as our bedroom which is overheated compared to the children's room. Dhartung's book recommendation is only $8.00 used, which is cool.

I don't believe we have valves on each duct but I'll check. I suspect our electricity bill is going up, but we are also essentially doubling the usable size of our house. Everything else will wait until we finish the basement properly, with the exception of a second thermostat.

but feel free to keep contributing to this thread if you think of anything else!
posted by mecran01 at 1:18 PM on January 23, 2005

My guess is the "bare cement with framing" is sucking the heat out of the space. As noted by dhartung, it's cooler underground, and concrete is not a great insulator. Typically, the temperature deeper than a threshold depth below ground is the mean year-round surface temperature. In someplace like upstate NY, that temperature is around 40F. I don't know offhand what the threshold depth is. Shallower than the threshold depth, the underground temperature varies somewhat with the surface temp.
posted by Kirth Gerson at 1:34 PM on January 23, 2005

I don't think anyone else mentioned gluing up rigid insulation panels to your concrete walls; this may help as well. You're probably going to have to do a bunch of things, each of which help a little.
posted by RikiTikiTavi at 8:38 PM on January 23, 2005