Best Of

with a slab on grade you will want to insulate it regardless if the heating type

At that point the cost if the pex is all you need to have clean, quiet , comfortable radiant system options

If you use pex you have many heat source options electric boiler , heat pump, wood, lp, solar

Find a knowledgeable local contractor to run some load numbers and give you options

I met a handful of knowledgeable hydronic contractors in your area on a recent training visit up there.

Hannah, at macleodandgrant.com could probably get you some names

it doesn’t have to be all or nothing. If going with a ducted heat pump, electric resistance radiant in the bathrooms would be a nice feature.

slab on grade is a cold floor no mater air or water heat.
insulating that slab helps but doesn’t elements cold spots.

I would argue that deliberately putting a concrete floor into your house is a major hit to comfort. I'd much rather have a wood floor and ducted heat. Concrete is just a really lousy residential flooring.

When considering air to water HP in cold climates a units peak capacity must be ignored. Capacity drops substantially in the deep cold. A heated slab offers great thermal stability and comfort as well as low system return water temperatures. If the radiant design shoots for the lowest return water temperature possible the COP can be in the 2 range at -8C OAT. For OAT's near 0C closer to 3 is possible. HP really wins in the shoulder temperatures above 0C. The more hours operated in that range the better a heat pump looks.

As said above the comfort from heat radiating from a slab to heat a space is great but the floor, by touch, won't be the idealized toasty warm surface most people think of. The floor won't suck the heat from you either. The desired flooring plays a roll in this choice. The blower equipment space, noise, ducting, vents, grill noise and air currents must be considered while looking at air to air if not going duct-less. If you are thinking ductless the fan units must be in your design atheistic. These are the costs of cooling. The need or desire for cooling is a prime factor in design choice. Ductless air to air HP can't be beat for investment dollar for both heating and cooling. Is it the best heat? Many argue it's not. How important is that to you? If heating mode is the the vast majority of the season, weighing the quality of heating vs the ability to cool for a tiny % of the time is a hard call. A HP radiant slab with good cooling is possible with chilled water mini split style ductless units or with a duct system for added money and complexity. Budget, aesthetics, simplicity, comfort, deep cold performance, cooling, there's a lot to consider.

”if” is looking pretty optimistic here 😅

people are understating the operational cost savings of a heat pump in this thread, especially given the author’s stated temperature range. This happens a lot here. Note the OP is using Celsius.

I agree with @Hot_water_fan, the included AC capability of a ducted heat pump combined with its 75% lower operating cost seems like the obvious choice here. Your area may have incentives as well to consider.

Ducted air to air is the way. If you ever need AC, it can do that too. No compelling reason to mess with hydronics on a low load new build.