How can I improve my crawlspace's heating efficiency in the winter?

Question

Home is located in NE Pennsylvania. Some details:

Crawlspace

• Runs entirety of the home's footprint (~1000sqft)
• Approximately 5' high
• 1/2 (2.5') Below grade
• Vapor barrier on the floor, sump pump
• Cinder block walls, piers
• Incoming water pipe, water heater (40gal tank, electric), and water piping for home is in crawlspace
• Has vents to outside - closed in fall/winter (condensation not an issue in NE PA)

Currently I have an electric heater hanging from the rafters set to about 48º that is thermostatically controlled (this one: https://www.amazon.com/gp/product/B0000AXEZV/ ). This heats the crawlspace during the cooler months to maintain an above-freezing temperature.

The home is occupied only on the weekends in the winter, and empty during the week. While unoccupied I turn off the incoming water with a valve, and drain the upstairs completely. The downstairs (just above the crawl space) is not drained. Rooms without plumbing are shut, rooms with plumbing have baseboard heaters set to 42ºF with the doors/cabinet doors opened.

(some details about inside: there is a single mini-split unit in the main area of the home set to 48ºF that maintains the temperature in the entirety of the home while unoccupied. Also inside is a newly-installed propane ventless fireplace with millivolt remote and thermostat feature - minimum setting of 45ºF. (I haven't tried using this to maintain non-freezing temps yet - not sure how I feel about having a fire burning in an unoccupied home).)

During January/February, 2019, while unoccupied the temperature would approach 0-15ºF, and the total daily energy usage would approach 60-100 kWh. Taken over a month at about $0.13/kWh, and an average usage of 80 kWh, this is about $10/day to heat the the crawlspace to 48ºF.

Fuel options in the home:

• Liquid Propane - 120 gal tank exposed to elements
• Electric (120v or 220v)

Here are some ideas I've considered to reduce crawlspace energy usage:

• Heat tape on the pipes (plugs into 120v, heats only the pipes)
• Install foam insulation board between piers below house and reduce the footprint needing heat (the pipes and water heater are on the front half of the 1000 sqft crawlspace - could reduce "envelope" to 500sqft)
• Install liquid propane heater (I've read about condensation issues with propane heaters in crawlspaces - and combustion danger)
• Drain the pipes (this is inconvenient because we use the house on the weekends)

Does anyone else have a similar plumbing situation / weather / occupancy rate in their home and have opinions on the suggested solutions for reducing energy usage while making sure the pipes don't burst when the temperature drops outside?

Answer 1

When I lived in Ohio I had my water heater and a pressure tank in a room under my front porch, their was a full basement. Trying to save some $ used foam board insulation around the two and used a small milk house heater on low set to ~ 40 degrees. then I had pipes in the floor freeze, I used heat tape it was a self regulating kind for use under a floor of a house I think it was made by 3m but that was many years back, after putting in the “foam room” and 2 strips of the heat tape our power bill dropped by 50$ a month and we never had another frozen pipe. My neighbor had a similar setup but used a heat lamp 300w but he did not know when it burned out and still had frozen pipes. I think the small heater was better because it had a thermostat, he said the heat lamp was better because it only drew 300w my heater was 1k or so on low and I use a similar heater today in my pump house they last a really long time if not turned All the way up and moved around. so that would be my suggestion a small insulated space and heater , then self regulating heat tape , make sure it is made for use under the floor, the last batch I purchased was by easy heat called freeze free, you have to buy ends separately but you cut it to length and it is listed for use under mobile homes and they are the fastest burning structures I know of, I only started using it 2 months ago but the end kits are way easier than the 3m type I have used in the past. (No connection to either product just make sure to find one for inside use)

Answer 2

Insulating the crawl space exterior walls, and/or partitioning the crawl space, seem like good ideas. Spitballing some numbers 1000 sqft might have four walls of 32 feet by 5 feet. It would take about 20 sheets of 4x8 foam board to cover that at US$20-$35 each for 1-2 inch thickness. It's easy to see that costs more than one month of heating, but it's hard to estimate the savings it'll create.

Heating and insulating the supply pipes directly cuts the need for heat in the crawl space dramatically. If the water heater is left powered on, and if you're willing to do a bit of plumbing remodeling, you could potentially set it up for recirculation. The water heater would then be the sole source of heat and you wouldn't have to fix heat tape to all the pipes.

Don't forget to check the crawl space for drain traps - below any bathtub, shower, or floor drain for example. If your solution allows the crawl space to get cold then you'll have to protect those drain traps somehow. Either heat them too, or make it a routine to pour RV antifreeze into them after use.