I would suggest looking into a geothermal heat pump, that with only one system provides in-floor radiant heating, forced air heating and air-conditioning with zoning, if needed and at least some of your domestic hot water.

You will have to do your own calculations to determine if this solution is a viable option in your case. I would suggest weighing the cost differential between geothermal and other options considered. First costs are always the lowest when regarding new build verses a retrofit.

Waterfurnace Synergy 3D

IMPO

SR

What would be the source of heat for the first-floor radiant?

armoured, it will be a propane powered water heater

If the house is designed to current IECC energy codes or better, the 1st level radiant could probably handle most of the home's heating loads including 2nd level. If upfront costs and operating costs are important, you may want to reconsider radiant floors and propane as main energy source.

Here is [recent thread on propane[(https://www.houzz.com/discussions/energy-star-most-efficient-2019-boilers-help-reading-the-stats-dsvw-vd~5649781?n=36) boilers. To summarize, propane is the most expensive common fuel. It would cost less to heat your home using electricity, as long as you choose high efficiency heat pump options. Cold climate heat pumps are available for your climate so choose a contractor who is comfortable with them and follow their guidance on any needed backup. Tough to beat woodstove with frequent power outages.

Radiant only provides heating so it's a tougher choice if the upgrade costs are worthwhile in your climate. Cold climate heat pumps can satisfy heating needs with generally less upfront costs. Ductless heat pumps are packaged systems that are easy to install. Providing sweat equity for radiant floors will be needed to compete in upfront costs. Tubing, manifolds, pumps, appliances, controls, pipes, all done in custom snowflake fashion. Giant propane tank, piped fos$il fuels into house, combustion exhaust to expel, hopefully not backdraft.

Most people choosing radiant are going off experience based on inefficient homes. Building to current codes changes the comfort dynamic and some find radiant less comfortable due to thermostat delay response. Radiant floors rarely make economic sense for efficient homes.

Why isn't a proper HVAC engineer planning this out?

The type of heat is immaterial; you need proper load calculations done.

There are new heat pumps that work okay (just okay) in very cold weather, but all heat pumps work better in more moderate temperatures. The problem is that you are planning to use them ONLY in the really cold weather, when you need supplemental heat.

"thick insulation codes" means absolutely nothing. What's the R value (walls and ceilings)?

Radiant floor heat is not going to pump out enough BTUs to warm 2 floors. It's not like radiators or baseboards; it doesn't get that warm and it doesn't provide the convection needed for circulation.

No heating design for a 2-story house plans to have heat on only one floor; it makes no sense.

Agree with proper load calculation. Heat pump analysis not so much. Both Efficiency Maine and Efficiency Vermont point to cold climate heat pumps as main heating source.

A 3 story home could be heated with one radiant floor level. Depends on design. Code and design conditions will warrant other sources, but for majority of time, heat rises and can be kept in place with air sealing, insulation and good windows.

It shouldn't be hard finding HVAC engineers to design for propane radiant. Harder finding engineers to design with best available heat pump equipment but similar to making extra effort finding builders and designers who can comfortably achieve better building envelope performance. Efficiency Maine and Efficiency Vermont are good places to start.

I admit I also don't understand why, in a new build, you wouldn't just extend heating system (be it rads or ducts or whatever) to the second floor. If it's a hydronic system, you can have thermostatic valves to keep them off when not needed for heat. Whatever you do, makes more sense to have proper calculations done and install at time of build rather than taking a risk and not installing a complete system to begin.

Springtime Builders: Radiant floor heat uses water temperature of only 80 to 85 degrees. Radiators and baseboards use water at 150 to 170 degrees. Radiant floor heat does not carry enough heat to heat additional floors; there's just not enough BTUs of energy stored in it.

Plus, at 80 to 85 degrees, the floor is barely warmer than room temperature and cannot establish convention currents that carry the heat to the upper floors. In fact, in a room with a cathedral ceiling, the living zone at floor level is warmer than the air in the upper part of the room.

Efficiency Vermont is comparing heat using resistance electric baseboards and oil heat to the cold-air heat pumps. Of course they will be better. But: that's for supplying all the heat--averaging both when the temperatures are in the 40s, 50s, and 60s (when it's efficient) as well as in the single-digit and minus 0 temps, when they are not as efficient. The problem here (in the OP's scenario) is that they will run ONLY in the lowest temperatures (as make-up heat), so they'd be running only in the temperatures where they are least efficient.

However--given the impossible scenario that he's given (and without any sense of what the R-values are), in reality, those units will run a LOT more than he expects, and in much higher temperatures.

If this were a good idea (or a workable one), you might find people doing it. But you don't.

If properly designed to the heat load... it makes no difference if it is a radiant or resistive or ng. ( cost of course will be different)

BT: Right. But that wasn't the issue. The issue I was addressing is that Efficiency Vermont is comparing heat pumps in their normal mode of use to the other energy sources (but not natural gas). But the OP isn't planning to use heat pumps as a full replacement--only as a backup in the coldest temps, where they are least efficient (and more expensive to operate).

But, as I also pointed out, his plan is destined to fail because the in-floor heat can't pump out enough heat at 80 top 85 degrees to heat the whole house. You can't boil a pot of water with a candle.

There's no way heat from the ground floor will heat a second floor evenly and thoroughly, unless the second floor is a loft with an open floor plan.

I don't know. I am surprised but our second floor system never runs. We are in a milder climate of course but also with lower insulation levels. Our second floor has less windows which I think is our biggest source of loss. We have a U shaped staircase and the heat makes it up just fine.

The R-76 in the attic might be why....

OP - heat load is an amazingly variable thing. If the walls are thick enough, body heat can warm a house (I exaggerate of course). There was a house I heard about that used double walls and just used electric resistance baseboard heat - was like $30 a month. In Montana. With new construction, insulate and air seal well. It makes for a very comfortable house that also is cheap to heat.

(Back to the body heat issue - we have a master that is zoned separately - we were comfortable with no heat at 15 degrees - room got down to 62 though - from 66 in the day).

Not unheard of by any means, just as with experience of first poster. It's mainly a question of air-sealing and insulation. Some Passivhaus are known to be heated with little more than body heat, lighting and appliances. In net-zero designs by South Mountain Company, homes lower than passive house standards, have space heating loads less than water heating.

It doesn't take passive house or net-zero for heat pumps to be more affordable than gas heating.

Recently plugged all 50 states into Efficiency Maine's home heating calculator, only 11 saved on simple energy costs with natural gas furnace instead of ductless heat pump. Discounting CA and AK, the gas minority had only a 7% advantage. Accounting for monthly, minimum gas fees or additional gas infrastructure can cut into that small advantage and make heat pumps more affordable in all markets which is more likely for efficient homes. No notable utility markets with propane furnace/boiler energy costs less than those of ductless heat pump.

If working with professionals that claim heat pumps don't work in cold weather, find someone else who is familiar with current market. Many are rated at 100% capacity down to temperatures of 5F, some have capacities over 80% at -15F. NEEP has ratings of cold climate heat pumps and use 5F as a design temperature.

As noted by Efficiency Maine: "More than 30,000 high efficiency ductless heat pumps have been installed in Maine homes and businesses over the past five years. Long used for cooling in warm climates, heat pumps are now one of the most popular technologies for heating in cold climates."