It's so very, very cold...

September 30, 2009 10:26 AM

I have an uninsulated sunroom that gets pretty chilly in the winter, and want to make it so that it is at least room temp. and can be used for plants (without breaking the bank). Any ideas?

My house has a sunroom that was built on to it, and I would like to use this room like a greenhouse for my houseplants. It isn't really insulated, and it has 3 very large windows and a sliding glass door. The floor is ceramic tile. I would like to not send my electric bill sky-high. I usually have to keep the door between the living room and sun room closed from late October until about March or April, because I am in Indiana where it is so cold (and it sucks) and cranks up my heating bill.

My idea was to use Gila Heat Control Light window film, to keep heat in. Then I wanted to use free-standing plant lights of some sort (so I don't have to drill holes, if I don't have to).

Does anyone have any ideas about how to best accomplish this? Has anyone tried any of the Gila films on their windows? Can anyone recommend a plant light? Thanks in advance.

posted by bolognius maximus to home & garden (10 comments total)

Do you need to be able to see clearly through those windows, or do you just need them to be insulated and to let light through? A relatively inexpensive way to insulate windows is to use a couple layers of bubble wrap, which won't be as effective as fiberglass insulation, but will help, and will allow light in at the same time, although you will lose your clear view through the windows..

You might want to do some research into what portable greenhouses are made of, because that is probably what you are going to want to use. If you own the house, and are willing to put in some money, you could install greenhouse glass, but I don't know how much more effective that is than a regular double layered window.

If you have access to the underside of the floor, make sure to insulate that. If not, consider getting some thin sheets of insulation, putting that on the floor, and putting another layer on top of that. You will also want to insulate the ceiling as much as you can.
posted by markblasco at 10:35 AM on September 30

Double or triple insulate your glazing with plastic film. You can buy 3M and knock off kits that just stick to your window frames and are tightened with a blow dryer.

Cover non south facing windows with some kind of insulation. Metallized bubble insulation is the easiest though only marginally effective, a layer of rigid insulation like Dow's blueboard would be better. The XPS can be covered with either thin MDF or wallpaper to make it look less white trash and to protect it from UV.

Fit the south facing windows with heavy weight insulative drapes that can be kept shut when the sun isn't shining on you sun room. Rigid panels can be used for this purpose too though day time storage of the panels can be a hassle.

If you take these steps and day time temperatures rise to high add more mass to your room with either concrete blocks or containers filled with water. A layer of milk jugs filled with water under your plants is a good first step.
posted by Mitheral at 10:37 AM on September 30

Gila Light Heat Control Window film is actually intended to keep your room cool. It prevents sun from getting in and warming up the room. Definitely don't do that!
posted by musofire at 10:55 AM on September 30

There was a page I read recently about a man who built an awesome greenhouse in his back yard. The one idea they had there that I had never seen before was to keep a large pool of water in it to stabilize the temperature. I believe it had solar panels to heat the water during the day and would then just stop (or slow) the pumping at night thus letting the heat radiate out of the tank.
posted by chairface at 10:56 AM on September 30

Gila and similar films are great for reducing sun load in the summer but will provide very little additional insulation. If you do not have storm windows now might be the time to add them. Adding the plastic film per Mitheral will also work but it does not always look that attractive. It's not unattractive though. Adding insulation to the roof would help most of all. Is there any access? Walls are next but that will be quite difficult.

There are foam panels for insulating basement walls. Perhaps these could be added and then papered or paneled over on the inside. You will have to redo all your outlet boxes though to bring them up to code (be flush with wall, not recessed).
posted by caddis at 11:05 AM on September 30

The key is keeping the soil warm, heating the air will gain the plants some humidity but won't help them as much as toasty soil. Fortunately, heating small amounts of soil is a lot cheaper than heating large volumes of air.

I'm in a climate that rarely dips below 30F in winter (sooo not Indiana) but I keep my tropical plants in a small uninsulated greenhouse plenty warm (soil temp of 80F) by running a 50 bulb string of mini Christmas lights around their pots. And also, for my divas from Borneo's lowlands: a seed mat under their pots. I have these hooked up to a timer so I don't inadvertently cook my plants during the day, for your climate you could try just leaving them on 24/7.

If you really want to get into it: greenhouse heaters.
posted by jamaro at 11:41 AM on September 30

It sounds from your description like you have uninsulated walls (and possibly floor & ceiling) in your sunroom. If that is the case, you should concentrate on insulating the non-window parts of the sunroom as a first step. It is much easier and cheaper to reduce the heat loss through the uninsulated walls than it is to reduce heat loss through the windows. Make sure to install a proper vapour barrier when you insulate or use an insulation material that is also a vapour barrier (like spray foam insulation). You should also consider air sealing to reduce heat loss (sliding patio doors, in particular, can be very leaky).

The heat control film you mention is not going to help you at all (in fact, it will probably make things worse). The film is intended to block heat coming in (i.e. from the sun) not block heat from going out (i.e. radiative heat from indoors). You want to let heat in from the sun and block heat going out from inside, so you want low-E (low emissivity) window film.

If you can get your sunroom to start to heat up significantly in the winter, then you can consider thermal mass (concrete, sand, water, etc.) to absorb heat during the day and emit heat at night. You may find that you need very good insulation, air sealing, and even new windows and doors to heat up the sunroom in the winter. If the room isn't south facing, you may never get there.
posted by ssg at 12:11 PM on September 30

Thanks for all of the answers. There is no way to insulate the walls. They are bare brick. Storm windows are out too, as these are large, sliding glass windows. I am a little confused about the Gila film. The product page says that the film is low E and helps retain heat, but opinion seems to indicate otherwise. But so far good suggestions...
posted by bolognius maximus at 12:55 PM on September 30

I assume that this is a brick wall without a hollow interior that could be filled with insulation and that it is brick on both the inside and outside. There are exterior insulation systems, like a sprayed on imitation stucco. There have been such problems with these systems that I would avoid them. Basically if water gets in between the exterior insulation and the old exterior surface everything rots. You can add insulation to the interior. If you want to keep the visual appearance of the interior brick then you are out of luck. You could add basement foam style insulation or add studs and use regular insulation. Then you sheet rock the whole thing, not particularly cheap, but not that expensive either to get use of a room for that many months. If you are really tied to the brick look you could even put a brick interior.

The reason the film doesn't help much on the windows is that it is not very thick. The film Mitheral suggested is even thinner but you don't apply it to the glass but leave it spaced apart from the glass. The air trapped in between the film and the glass does essentially all of the insulating and air is a magnificent insulator.
posted by caddis at 2:34 PM on September 30

I did forget to mention that the low E films are radiant blockers. They block the radiant energy coming in with summer sun but also block radiant energy leaving from your room to the cool winter environment; you know that feeling when you are standing across the room from a picture window on a cold winter night and the air in the room is warm but that window seems to suck the heat out of you, it really does, and that film will reduce that and also from all the other warm spots in the room. I think the conduction on a single pane window completely overwhelms the heat loss from radiant losses. I just spent ten minutes trying to answer that and my google fu was inadequate, really inadequate.

There are three forms of heat transfer: convection, conduction and radiation. In convection cool air mixes with warm air - you have holes in your wall, such as around switch plates, under door sills etc. In conduction warmth flows to cold, excited molecules excite the molecules next to them and so on and insulators slow that down. That is you putting your warm hand on the cold glass and feeling the cold. Radiant transfer is one body of one temperature sitting next to another of a different temperature and there is not convection or current of air, water etc. to move the heat, and it doesn't move through the media (air, metal, etc.) between, but it moves like light passing. This is how the sun warms us, it is hot, we are cold, there is essentially vacuum between us but that huge temperature difference warms us and cools the sun.

I think radiant transfer through a single pane window represents a small part of the total heat loss and thus adding this film will not help much with overall heat retention. I could be wrong so maybe if you spend more time looking you will find better answers in terms of percent heat loss through windows. With modern double and triple pane window etc. those percentages likely change. Also, if the window is really old and leaky then convection will dominate. So, back to Mitheral's film, it solves both of the biggies for older windows, convection and conduction. Also, a curtain will solve radiant heat loss and also help with the others.
posted by caddis at 6:44 PM on September 30