Return to the Growing from Seed Forum | Post a Follow-Up

questions about heating mats

Posted by kawaiineko_gardener 5a ( on
Wed, Feb 23, 11 at 15:55

Basically I have two main questions.

what size would I need? I'll be using a 48" grow light,
and somebody said with a 2 foot grow light, I can use
one heating mat; with a 4 foot grow light, I can use two.

My question is for a 4 foot grow light, which size heating mat should I use? Basically I just need it to be big enough to cover the entire area underneath the grow light.
As a result, I need to know what the length and width
of the heating mat would be, that would be a big enough size for the 4 foot grow light.

I would also prefer to get one big heating mat that will
fit under the 4 foot grow light rather than 2 smaller ones, it will just save me money.

The largest I can afford would be the medium-size heat mat, but would it be big enough for a 4 foot grow light?

Here are the sizes:

9" x 19.5" (small)
20" x 20" (medium)
48" x 20" (large)

2nd question; are all seedling heat mats waterproof? I found some on Amazon but it doesn't specify whether they're waterproof or not.

The sizes for the heat mats I've found are:

Follow-Up Postings:

RE: questions about heating mats

I bought a 9x19.5 mat from amazon with tray and dome for about $22.50. It is a rubber mat with heating tape molded in, is water proof, but when I placed it on the carpet under shop lights the heat went up to 110 degrees by the next morning. I am going to run it through a light dimmer switch to lower the heat. Just sitting in on a table top will help lower the heat.

I would advise using a therometer to make sure the heat is in the range you want.


RE: questions about heating mats

I can�t tell you whole lot because this is my first buying a heating mat too. But what I did find was the Hydrofarm listed on Amazon and it gives a little more information. Plus the guides are listed as pdf at the bottom of the link.

Here is a link that might be useful: Seedling Heat Mat 9

RE: questions about heating mats


4' is 48" inches. So the large mat that is 48" long is the best fit for covering the entire length under a 4' light. The medium length of 20" is going to leave you with a lot of unheated space under the lights. This could work for you, however, if you put the seeds that have not germinated yet on the mat and the seeds that have germinated in the unheated area. Once seeds have germinated, they no longer need the heat mat.

The Hydrofarm heat mat I have seems to waterproof to the extent that a little water or condensation on it doesn't cause any problems. I'm sure it wouldn't be a good idea to submerge it.

Larry, the Hydrofarm heat mat thermostat that I've been using is working really well to keep my mat from getting too hot. Whenever the mat reaches the temp I've set it at, the thermostat turns off the power to the mat. I think this will prolong the life of the mat too.

RE: questions about heating mats

I've used heating pad for your body. A LOT cheaper and you just have to be careful when you water, but I have even gotten them wet but would not recommend that. I'm also thinking of using an electric blanket. I am trying to burn m y house down? Anyone have an opinion?

RE: questions about heating mats

Many heat mats are made with a thermostat as part of the mat and are usually permanently set for about 70 degrees. Al

RE: questions about heating mats

Razkeys, I use a heating pad to start my seedlings and it works a charm. I think a heating blanket is pushing it though. I put my seedlings on a cookie sheet to keep the water contained and off the heating elements of the pad. I picked up more stuff for seed starting at goodwill and other thrift stores.

RE: questions about heating mats

Right now I am using my home-made heat mat(9"x13" cake pan) with Christmas tree lights under it. I only have one 9 cell in it now. I can look over on the bookcase and see it is 76.1 degrees inside(transmitting therometter) and can addjust up or down as I see fit. The major drawback is that I have to have an extenion cord running to it from the switch I have set by my recliner.

I have a Hydrofarm 9.5x19.5 mat that gets too hot, but I will fix it like the homemade (pan) by using a dimmer switch on it. The home made runs about 85 degrees at 80 volts (temps vary with ambient).

I like having a small heatmat (pan) and just sticking 1 or 2 cell packs in it and sliding it under or behind the chair
and just glancing over my left sholder to check the temp.


RE: questions about heating mats

Here is a something cheap to make and I got all the stuff at Lowes. I made this last year and it worked good. Its nothing but a 5 gallon bucket and a light socket. I dont keep my seedlings in there after they are up because of no air movement.
Check It Out!

Here is a link that might be useful: CFL bucket

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Growing from Seed Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here