Window Heater

A more sensible approach would be to replace the single layer of glass in t he window with double-glazing. You can use a second sheet of polycarbonate space off from the glass by about 10mm to dramatically reduce heat losses.

In the UK this was called secondary double glazing and you could buy a kit of parts at do-it-yourself shops. Typically it went onto the window frame, rather than onto the glass itself.

If the window is deep enough, you can just measure the dimensions of the wi ndow, order a suitable double-glazed pane from your neighbourhood glazier, and replace the existing single pane of glass with the double-glazed assemb ly.

I've done both. The replacement pane is neater. Don't forget that window gl ass isn't a tight fit inside the window frame - you need a 6mm (0.25 inch) gap between the glass and the frame which is filled by putty or non-setting glazing compound - to take up differential expansion.

Triple glazing is even better. Apparently the Swedish love it. The panes ge t a bit deep.

Try facing the styrofoam with kitchen aluminum foil (unless you want light to come through, of course.) It will be an IR reflector, and may substantially improve the insulation effect of the styrofoam.

Jon

What part of my post made you think the glass was single pane???

I tried it. The window is already double glazed and I added a layer of plastic sheet (they sell kits for this). It helped, but no more (likely less) than the 3/4 inch Styrofoam. I don't recall if I've tried both.

My original idea with the heater was to add the plastic with the heater in the space between the plastic and the Styrofoam. I expected that to use very little extra heat. But I don't like the plastic sheet and wanted to try this.

Now that I think of that, heating the space behind the plastic reminds me of your ultra fine temperature controller. You put the sensor and the heater at the thin spot in the insulation. Heating the space in the window would completely stop the draft.

The surprising part of the whole thing is just how small a temperature difference will result in a draft. I only measure 2 or 3 degrees difference between the Styrofoam and other objects in the room, yet the draft forms when it is very cold out. Likely the walls also create a draft, but not as pronounced. Sitting with my back to the window doesn't help, but like I said, no practical way to deal with that.

That would help if there was much temperature difference. But the inside is only three degrees (F) different from the rest of the room. Maybe the temperature difference on the other side is greater. But 3/4 inches of Styrofoam is a *lot* of insulation. I believe it is equivalent to four inches of fiberglass.

I think the insulation is very good at this point. The problem is there will always be *some* heat loss and it doesn't take very much at all to create a draft albeit a small one. The issue is not so much that there is a draft even, it wouldn't be noticed if I didn't have my back right up to it.

Hmmmm. the heater is toasty!

Have you considered that, rather than a draft, your chill is due to radiated heat loss? There's low-E options on double glazing, that are intended to take care of that. It costs a few extra dollars when your glass shop takes the order, though.

There are two cheaper versions.

One: take clingfilm and sticky tape it to the window frame, then play a hairdryer over it to make it taught. Optionally replace the tape with whiteboard magnets, to make it a little removable.

Two: gardeners insulate their greenhouses with double-walled bubble wrap. I presume you could also use two layers of single-walled bubble wrap, which would be easier to obtain for a quick-and-dirty experiment.

Both have the advantages of allowing light through and stopping draughts around the window, and help to reduce heat loss.

I doubt either would be very effective for the OP's case.

I suspect the OP's other options would be to wear an anorak/salopettes, or to have a baffle that guides the draught elsewhere in the room.

Radiated heat loss through 3/4 inch of Styrofoam??? Really?

I balk at putting tons of insulation on myself, but I tried redirecting the draft. I used to have a piece of cardboard behind the blinds that tended to keep the draft at the edges. It sort of worked, but only if I stayed right in the one spot.

I would add the plastic, but when I've done that before the tape provided is pretty marginal and comes loose pretty easily. Also, for some reason the varnish on my window tends to come off with the tape. It may have some water damage.

Consider using less electricity by plugging yourself into the mains. Not directly, but via one of those things for the elderly that is effectively a 1 sq ft electric blanket for keeping the kidneys warm.

Or occasionally sticking a hairdryer's outlet under your sweater :)

Yes, it would only shift the problem :)

A long curtain should could deflect the draught down to floor level. Blinds, whatever that means, seem pretty sub-optimum.

Painters "masking tape" is low adhesive, since it is designed to be removed. No guarantees though.

The setup is not completely clear to me, is it a vertical window in the wall, horizontal in the roof or an angled one ?

argon filled 2 or 3 pane window with low-e coatings and a radiator under the window. The radiator creates an upward airflow, which keeps the feeling of draft away. Typical power is 50-200W or 500-700W if you heat the room with the same ones.

The fact that you could feel a draft.

Making the gap too big allows convention currents between the panes. Styrofoam is essentially stabilised air - the individual cells are too small to allow convection.

The "ultra-fine" temperature controller was aimed a getting tight control of temperature over a volume about 1cm square and less than a millimetre thick.

As the paper said, we could have done better if we could have insulated the volume of interest better, and hadn't had to leave clear spaces for access.

You want to get rid of a specific temperature gradient, essentially from the middle of your window to the wall surrounding it.

Putting a heat source in the middle of your window may well do it.

The high-tech solution - as used in car windows which you don't want to mist up - is an electrically conductive and transparent layer of tin oxide.

Curtain? A draft is just a convection current, and if you confine that convection current so that it doesn't actually run down you back, you should be fine.

If you wanted to go very high tech, you could work out the Rayleigh number.

It does depend on the cube of the characteristic length, and making the convecting volume thin does help.

You might try something like a gutter to catch the cold air with a down spout to direct the cold air to the floor.

You could mock this up using some cardboard to determine if it is a satisfactory solution.

This would not use electricity for heating, which ought to be more economical.

If you use resisters you might mount them on some heat sinks.

Dan

I hate cold... that's why I came straight to Arizona upon graduating from MIT in 1962. ...Jim Thompson

put a lamp with an old-school incandescent in the windowsill ? :)

Alright, so move the window.

Tim

Is it the window or the whole wall?

I suspect the key idea is "heat output" if it's used properly. If you're dissipating 50W then you're dissipating 50W and that's your heat flux. If you spread that flux over a larger area the _temperature_ of your heating assembly will go down, but not the flow of heat.

And, I suspect that as long as you maintain the heat output, spreading it out vertically to reduce the temperature won't change it's effect on the draft -- you just want to heat the air, you don't care if it happens over the space of 1/4 inch or ten inches.

If you just can't get there from here, putting a strip of resistors inside a cage of chicken wire (or something more decorative) would work as well as what you have now, with less risk of injury.

So you spend most of your time sitting by a drafty window wired with power resistors?

Do people like, call those nice people to check in on you from time to time or...

It has been a quite mild winter here, only once near -20C. The temperature range I have seen here, on the south coast of Finland, is from -36C to +34C.

A wire-strip heater at the bottom could create an internal circulation to heat the small gap a little, and create a light surface draft that goes up instead of down. Would such a draft also be a problem?