Most Ontario houses switching to a heat pump keep the ducts they have. Most of the time that works. Sometimes it does not, and the owner finds out in January when the back bedroom will not get warm and the air handler sounds like a jet on takeoff.
Here is how to tell which camp your house is in, what it costs to fix, and why the answer starts with a heat loss and a ten-minute pressure test.
A gas furnace heats air hot and pushes a smaller amount of it. A heat pump makes warm air, not hot air. To deliver the same heat into a room, it has to move more air.
That is the whole problem in two sentences. Ducts that were fine for a furnace can be too small for heat pump airflow. When that happens the blower works harder, gets louder, and still does not get enough air to the far rooms.
If your house already has central air that keeps up on a hot day, that is good news. Cooling also needs high airflow, so ducts that handle your AC can usually handle a heat pump of a similar size.
Had central air and it kept up? The ducts are probably close. Never had AC, or the upstairs was always hot in summer? Get the ducts checked before you pick a size.
If the switch needs a permit, the building department may also ask for the ventilation summary (RMVDS).
A CSA F280 heat loss gives you the heat each room needs on the coldest day. From that comes the airflow each room needs. Without it, everyone is guessing.
A technician reads the pressure in the supply and return with a gauge. Ten minutes. High pressure means small or restricted ducts. Do this before you pick a heat pump size, not after.
A lot of older houses have one or two returns for the whole house. Heat pumps need the air to come back as easily as it goes out. Bedrooms with doors closed and no return path are the classic cold rooms.
The rooms at the end of the longest duct runs, over the garage, or in a bonus room are where weak airflow shows up first. Check what is actually coming out of those registers.
Sometimes the honest answer is a slightly smaller heat pump that matches the ducts, with backup heat for the coldest nights.
Often the cheapest fix with the biggest payoff. An extra return upstairs can change how the whole system behaves.
Replacing a restrictive section of the main trunk or the plenum is sometimes all it takes. A duct design shows where.
A hybrid system lets the heat pump work most of the year and the furnace take the coldest nights. See hybrid heat pump design.
One cold room over the garage does not need new ducts in the whole house. A single ductless head can be the right tool.
In a gut renovation, or where the ducts were never right, a new duct design is the real fix. Cheaper now than after the drywall is up.
Matching the old furnace size. The old furnace was probably oversized to begin with. Matching it with a heat pump means a bigger, more expensive unit than you need, pushing more air than your ducts can carry. See why oversizing hurts.
Buying first, checking later. Once the unit is in, your options shrink. The pressure test and the heat loss cost a few hundred dollars. A wrong-sized heat pump costs years of comfort complaints.
Blaming the heat pump for cold air. Heat pump air feels cool on your hand because it is warm, not hot. If the rooms are holding temperature, it is working. If they are not, look at airflow and sizing.
Switching this year? Get the heat loss first. It sets the heat pump size and tells you what your ducts need to carry.
Get Free Quote →Often yes. If your house already has central air that keeps up in July, the ducts can usually move the air a similar size heat pump needs. If you never had AC, or the AC never kept up, the ducts need a closer look before you buy.
A furnace heats air to a high temperature and pushes less of it. A heat pump makes warm air, not hot air, so it has to move more air to deliver the same heat. Small ducts that were fine for a furnace can choke a heat pump.
A technician measures the air pressure the blower is fighting, in the supply and the return. It takes about ten minutes with a gauge. High numbers mean the ducts are too small or restricted, and a heat pump on them will be noisy and short on heat.
It usually is not cold. Heat pump air comes out around body temperature or a little warmer, so on your hand it feels cool compared to a furnace. If rooms are actually cold, the cause is usually airflow or sizing, not the air temperature.
In a lot of Ontario homes, yes. A hybrid setup lets the heat pump do most of the year and the furnace take the coldest nights. It also means the existing ducts only have to carry heat pump airflow part of the time.
To size it properly, yes. And in many municipalities the permit for a heat pump that heats the house will ask for one. A heat loss tells you the size you need, and the duct check tells you whether your ducts can deliver it.
Send us your floor plans or a sketch. We calculate the heat loss room by room and show the airflow each room needs, so you and your installer can check the ducts against real numbers.