Question: We’re in the process of building a cottage. We have a 42-inch-high crawl space. The walls and floor of the crawl space are concrete. The walls are sealed and insulated with fibreglass batts to R17. The main floor is standard floor joists with 5/8-inch-thick fir sheathing. We would like to install in-floor electric-heating cables in all the main-floor areas.
Should we heat the crawl space? Is there anything we need to do in terms of additional vapour barriers or additional insulation?—Tom Schell
Answer: Your question is one that I get frequently, but with the additional twist of the in-floor heat system. My answer will depend on the location of the heating cables and other factors, but the real question is about the capacity of your proposed system and its ability to handle the heating requirements of your cottage.
Heating an insulated and air-sealed crawl space is normally the best way to ensure both comfort for the occupants, as well as prevention of damage to plumbing and other components below the floor. This can be done with ducting from a forced-air heating system, pipes or convectors from a boiler, electric baseboards or other less conventional means. Depending on the heating system in the building, piggybacking additional heat for the crawl space may be a simple matter of ensuring there is adequate heating capacity for the additional space. If that is not the case, installation of electric baseboard heaters is simple and inexpensive, as long as there is a large enough electrical service in the unit to support the additional load.
Normally, any excess heat generated in the crawl space will rise up through the heated air into the building above. Some may be lost to the exterior through the perimeter crawl-space walls, but your good insulation practices should prevent that from becoming a serious issue. The heating will not only help to warm the flooring above, it may prevent any plumbing pipes under the floor from freezing during cold winter weather. Even with the concrete floor in the crawl space, a little additional insulation or air/vapour barriers may be required. The unusual item in your request is the installation of the electric-heating cables in all the main-floor areas.
Electric-heating cables work by turning the materials above or around the cables into a radiant heat source.
By heating this area with the electric wires — often stone, masonry or ceramic tiles — you will be turning the entire floor area into a radiant heat source.
The idea is that this surface will warm the building and its occupants by radiation, rather than primarily by convection with a forced-air system.
Because of this heating method, some of the heat from the cables will help warm the crawl space below.
If the cables are installed below the floor sheathing, which is possible, but not as common as above, that may generate enough heat for the crawl space. If the wires are more typically installed above the sheathing, embedded in a thin set mortar, then most of the heat generated will be transferred through the mortar and masonry flooring to the living space above. Some will undoubtedly heat the floor sheathing, but that may not be enough to keep the crawl space above freezing. So, location of the cables, floor-covering materials and other factors may have to be taken into consideration before deciding on the need for additional sources of heat for the crawl space.
While I am quite familiar with the method of installation and operation of an electric-grid in-floor heat system, I have little knowledge of the capacity of such a system. Only a person trained for this purpose would likely be able to answer your questions, taking into account the specific criteria mentioned above. Knowing the heating output of your proposed system, the volume of the space to be heated in the cottage and crawl space and the flooring materials would be requirements for proper heat-load calculations. A professional heating, ventilation, and air conditioning (HVAC) technician or qualified electrician should be consulted for this evaluation. They should be able to evaluate the building, insulation levels and other factors to determine the required heat-output capacity for your proposed system.
Even if you are intent on installing this system yourself, you will likely need professional help for planning this endeavour. Ensuring that you are doing the installation correctly with properly sized wires and circuit breakers is critical. Even more so, making sure you have proper heating capacity for the cottage is paramount.
If this is a new building, you will have gone though the permit process, which will require further inspections of the electrical and heating systems once roughed-in. If this is an older cottage, obtaining the proper permits before beginning should ensure that you do the job properly. The building authority in your area will review the plans and will likely require specific details or an accurate description of the proposals for the heating system.
A schematic diagram may be needed with technical specifications to satisfy local building-code requirements.
Heating the crawl space will absolutely be required for prevention of frozen pipes, condensation and other issues, but the real question is whether your proposed in-floor heating system will be enough to handle the job.
Only a qualified HVAC technician or electrician will be able to answer that question.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past-president of the Canadian Association of Home and Property Inspectors of Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or visit his website at trainedeye.ca.