Home built seedling warming tray

The sun room I have at my house has old single pane, aluminum sliding door windows which don't close very tight and is not insulated that great. It gets very cold in there, much too cold to grow little seedlings, especially the warmth lovers like Tomatoes, Peppers and Eggplants. I tried growing these in there, but I always had to wait until almost April to start them, because the room just did not warm up much before then. Even then it took a long time for those seedlings to sprout and then to grow to transplanting time. Being in the Northwest I learned with time one better get these warm season plants started early to grow them to a good size before transplanting in May to June, because you need a good head start to get them to produce due to the cooler summer nights we have.
Tomatoes, which can take a bit cooler then the Peppers and Eggplants did alright in that cold room, but my Peppers and Eggplant did not do so well and so most years I hardly got any peppers and no eggplants whatsoever out those plants. They were stunted in their growth and needed the whole season to recover, so hardly set any fruit.
Last year in a desperate attempt I cleaned off my sewing table, took apart the upper part of my light table and set up a small growing station in my office.

Which did work much better but I couldn't use my table for anything else and it also was not large enough of a growing area for the many plants I normally grow. I needed a better solution.

So this year I started looking at seedling heating pads with thermostats online to find 'they are very expensive' especially if you need 4 of them or the extra large sizes. I just was not willing to spend that much money on something being used only in the beginning of the garden season. How much technology is in that plastic pad anyway? Nothing I say what justifies the prices being charged.
But as I was researching these heating mats I kept coming across sites of people who built themselves warming trays with rope lights and I decided we would built one ourselves. Disclaimer: I made the decision and attempted to make a cheap version using old wire fencing and winding the rope through it, but my husband looked at it came up with a better way to built it. So in the end it was my husband who built it not me

                                      Here is the finished warming tray
                                                             
He used foil backed insulation foam for building the trays, since the reflective foil will channel the lights heat up to the seedling trays, increasing the heating potential with less heat loss. The rope lights are just sitting inside the foam channels, the whole foam tray is just sitting on my PVC pipe light table with the Plexiglas sheets sitting on top. The foam is strong enough to support the planting trays so we didn't bother put a wood shelving underneath. The lights are plugged into a seedling tray thermostat which is set at the right temperature for the seedlings being grown. Since the room is much colder at night and I did not trust the rope lights to keep up with the coldness I also covered my light table like a small green house in plastic sheeting which I open during the day, when it is warmer outside and the sun room heats up and close once the temperature drops.
The warming tray has made such a big difference. My tomatoes, peppers and eggplants have sprouted so much faster then normally and are making good growth. They look like happy little plants, healthy and all.


Here is how my husband built the warming tray:
These are the major heating tray materials you need. Foil backed insulation foam, 24' rope light, Plexiglas sheets and a heating mat thermostat if you want to control the temperature.
You also need 'Liquid Nails'  to glue
the pieces together and a sharp knife to cut the foam.    
All the dimensions are depended on the size of your growing area
or how large a tray you want to built.

First you need to
cut small, long strips of the foam for the edges of the tray.
About an 1/2" wide or slightly slimmer then that.

Which then get glued onto the top edge of the bottom foam pad.

Make sure you live a little gap on one edge for the light rope to be guided through like where the arrow is pointing to.

To be able to wind the rope light inside the tray we need to built some channels for it. So you need to cut some more 1/2" wide foam strips, a bit shorter then the others, because you need to be able to wind the
rope light around them.
We made two separate trays which are using one rope light. We had to separate our trays since my light table middle section is divided by PVC pipes as you can see in this picture. But we wanted to use one thermostat for both trays. So we wound the rope light from one tray to the other.
It would be easier and probably a better solution to use only one long tray for the whole area.
You could also make the channels a bit tighter then we did and use a longer Light rope.
I think it would maybe give you more heat then ours does, I just used what I had available. Anyway I measured the temperature with a minimum/maximum thermometer and the lowest the temperature has gone down at night was 59 F.

Here again is our finished warming tray.

Next season I might change it all to a longer rope light and see how much of a difference it will make.
For now my plants are growing nicely and I can see it is already making a big difference in the plants growing compared to the last years.

And I have a nice clean office with a clean table to do my other projects on.