Gregory in Québec asked:
I recently replaced my oil furnace with a heat pump/electric furnace system. I live in the region of Montreal. The heat pump can heat/operate in temperatures as low as -30c. The oil furnace had an air intake duck supplying the furnace with outside (cold) air. I understand this was necessary for an oil furnace. This component is still in place and presently supplies the electric furnace with outside air. One very qualified engineer told me that this component MUST be removed since it is no longer required with the new system and only adds unnecessary cold air and thus, increases my heating bill. Another (maybe less) qualified individual claims that it could be removed but rather suggests to leave it in place since it provides fresh air to the system and the entire house. Who is right ? What should I do ?
Hello Gregory,
They are both right and both incomplete, hence the reason for the contradiction.
THE NEED FOR FRESH AIR
All electric heating systems can filter your household air and get it to the right temperature, but in and of themselves they don’t get rid of stale air, nor bring in fresh air. In new construction, all electric houses are code required to have an air changer system that exhausts stale air and introduces fresh air to the house. If you pay a bit more, you can have a model that captures the heat in the stale air and warms up the incoming fresh air. The generic term for all of them are “air change” units, and the heat recovery models are commonly called HRV or Heat Recovery Ventilators. https://joneakes.com/jons-fixit-database/887-WHAT-IS-AN-AIR-TO-AIR-HEAT-EXCHANGER-HRV-and-ERV
When you downgrade your system to all electric, one of the hidden costs that is never mentioned by the electrician is the need for fresh air.
AIR SUPPLIES WITH A FUEL FIRED FURNACE
Traditionally with a fuel fired furnace there are two types of intake ducts: one that supplies outdoor air to the burner of the furnace, called a combustion air supply https://joneakes.com/jons-fixit-database/884-WHAT-IS-A-COMBUSTION-FRESH-AIR-SUPPLY; the other supplies outdoor air to the ductwork itself to introduce fresh air to the house https://joneakes.com/jons-fixit-database/1532-Can-I-close-off-the-fresh-air-to-the-furnace-return-duct.
Even with your fresh air supply dampened down to reduce its flow, it will significantly increase your heating demand, you are heating all that very cold air.
DRAWING FRESH AIR IS MARRIED TO EXHAUSTING STALE AIR
Jump for a minute to thinking about getting rid of stale air. Until you went all-electric, your chimney was probably the primary exhaust of stale air from the house, supplemented occasionally by bathroom and kitchen fans and the clothes dryer. When you go all electric, you have no continuous exhaust of stale air, hence a more polluted house.
In older homes cold air drafts came in through leaks in the walls, and stale warm air went out through leaks as well. In modern homes we block most of that air leakage. Enter the air changer – which both exhausts out stale air and in a balanced fashion brings in fresh air. Add in an efficient heat exchanger and you can recuperate around 80% of the heat going out, to pre-heat the air coming in. In my home, when it is -20C outdoors, the fresh air coming out of the heat exchanger into the house is about +10C, which is ejected near the ceiling where there is excess room heat and all we feel is fresh, not cold air. https://joneakes.com/jons-fixit-database/631-Overview-To-HRV-ERV-or-not-to-HRV-ERV Where you have an electric furnace with whole house ductwork, the incoming air injected into the return side of the duct system, comes quickly to room temperature before even getting to the rooms.
For the health of your family, you do not want to close off that fresh air duct, but if you want to consider both the health of your family and your pocket book, you will insert an HRV between the furnace ducting and the outdoor intake hood, hence your two experts can both be happy.
Lots more details via the links found in each of the above articles.
I hope this helps,
Jon