Here are a few ideas regarding heat aboard. (1) For freeze prevention, the idea is to sandwich your pipes, machinery and seacocks between a layer of warm air in the boat and (warm) water beneath the boat...so seal up vents, cover hatches, and seal engine air intakes for best efficiency. I stuff some insulation in my vents and under my cockpit floor in openings to keep cold from coming in around my fuel tanks and exhausts....open them in warm weather for air circulation. (2) I previously posted information on how I used 40 mil clear vinyl (enclosure) material to make interior "storm windows"....sticky velco plus staples, a few buttons... Depending on windows, 3/16" plexiglass with edge molding for stiffening is very efficient...I have that in my home.....magnetic stick on strips can also be used... These aree especially important if you have aluminum frame windows which frost on the INSIDE when it's really cold....Home storm window kits with two sided sticky tape and thin plastic sheeting also works well....my neighbor does that.... (3) I now use digital thermostats, battery operated, from Home Depot for my heating systems...It keeps a more uniform temp than the coiled bimetallic strip type...mercury can slop in boat movements so I never use that type. Also, it can be set as low as 45 degrees....I set the Webasto thermostat at 48 degrees when not aboard. A second heating system I have is a Surburban propane hot air unit. (Details posted about two years ago). I mounted a second digital thermostat for this sytem right next to the one for the Webasto...and leave it set for 45 degrees...It will run and operate only if the Webasto fails and temps drop a few degrees. I leave the remote switch for the propane solenoid "on" for this purpose, so a leak free propane system is a must.....The Webasto and Surburban systems operate from separate 12volt battery banks just in case of a shore power failure.... (4) Crossover valves enable one to hook up two propane tanks in parallel...when one runs out the valve automatically switches to the full tank....available in RV stores, maybe some marine stores...I keep two 40 lb tanks aboard and a third as backup...that way when I get low, I can fill two at once reducing runs...Two tanks will keep the boat from freezing for two to three weeks.... (5) By setting thermostats so cold, 48 degrees, when not aboard, I save on fuel. The problem with setting low theromstat is that electric heaters can't be set so low....So I don't YET have electric backup... I'm about to try a LUX baseboard thermostat (model LV 21042 22 amp, cost about $20, Home Depot).. Iit has a 50 degree setting and looks like it might be able to set to 45 degrees. I'd like this in case the two primary systems fail. I'll "cold test" it next boat visit.... (6) Nothing guarantees heat, so my last backup is human: A boating neighbor who lives aboard three of four days weekly checks a digital thermometer hung in a porthole ....The plexiglass window never fogs, so all he has to do is peek in and check the reading is over 40 degrees....A docklight even provides enough illumination for night time....The thermometer sensor is near the floor in a cold corner so it's usually about the coldest spot in the aft cabin where my thermostats are located...It has been reading 42 degrees during the current cold spell in the teens.... A temperature monitor/alarm and automatic dialer, as posted a month or so ago, is a good alternative....but I don't have a wireline service at the marina and don't want to pay for one.... (7) Once systems are installed and paid for, diesel heat is cheapest, propane next, and electric most expensive...so my systems are set up to operate in that same order.....Electricity in my NY marina is about 22 cents/kwh....very expensive. FINAL NOTE: This is not to suggest anyone shouldn't winterize....that is still the safest strategy if you are not living aboard. I don't winterize and instead leave heat on because the dog and I need to get out of the house from time to time to give the "admiral" (and her dog) time to recuperate.....and take care of maintenance and upgrade chores..... Cheers, Rob Brueckner 1972 Hatteras Yachtfish