AIR-TO-WATER (A2W) HEAT PUMPS DETAILS

Distribution System - Getting heat (or cooling)

Distribution systems are not specific or unique to heat pump systems; in fact they are similar to those used with the most efficient gas boilers. .

One important requirement they need to meet for heating: they must work well when the buffer tank temperature between 100F-130F, and thus compatible with output temps of the heat pumps.

We use one three types of hydronic (liquid-based) distribution systems for heating and cooling:

1. Radiant (floor heating/cooling)

2. Wall-mounted “Panel” Radiators (heating/cooling)

3. Hydronic Air Handler ("modern" forced air)(heating/cooling)

Choosing between these depends on factors such as:

  • new vs. existing (retrofit) house;

  • budget;

  • floor surface types (wood, concrete, marmoleum, vinyl, cork, carpet, etc);

  • square footage and air volume (cathedral ceiling or not)

  • basement vs main floor rooms vs upstairs bedrooms; and

  • cooling requirements (if any).

First, we are using the buffer tank as a reservoir of warm or cool energy that is pumped to manifold when a thermostat makes a “call”

Diagram illustrating a heat pump system, labeled "A2W HP," connected to a buffer tank and a distribution system (emitter), such as a radiant floor or radiator. Arrows show the flow of heat or cool air between the components, with energy storage indicated in the buffer tank.

Below is a pic (left) of a manifold with supply and return loops for a radiant floor  and (right) mechanical room with a buffer tank and two separate manifolds (lower one for radiant floor basement and upper one for main floor underfloor heat ):

Plumbing system with copper pipes and valves
Heater system with pipes and control panels in a basement.

RADIANT

Three images show the process of installing a radiant floor heating system. The first image displays orange tubing laid out on the floor. The second image depicts someone pouring concrete over the tubing. The third diagram illustrates the staple-down thin-pour method, highlighting heat flow directions.

1a. Staple-down PEX tubing (above) on top of sub-floor then covered with a <2 inch layer of gypcrete or lightweight concrete. Very efficient, responsive comfortable. >$10/SF.

1b. Aluminum heat plates on subfloor (above) and covered with 1/4" plywood then wood, vinyl, marmoleum or other thin flooring material with good heat transfer properties.Very efficient, responsive comfortable. D-I-Y friendly and $5 to >$10 per SF.

Radiant floor heating installation with diagram showing heat plates on a subfloor.
Radiant floor heating installation with heat plates and diagram

1c. Slab-on-grade 9

  • Pex tubing covered with 4-6 inches of concrete.

  • Works well but not as responsive as other radiant types due to the mass of all the thick concrete.

  • This is the most common in basements.

1d. Underfloor radiant. Not recommended unless aluminum heat plates are used. Install can be tedious but works well if done properly.

Images of radiant floor heating installation with tubing on insulated panels, and a diagram showing a slab-on-grade configuration.

2b. Wall-mounted Panel fan radiators

  • These are hydronic (liquid-based) radiators that transfer heat passively via convection.

  • No fan so heating-only

  • Very simple

  • Must be sized based on delivery temp of average 120F

  • $500 to $1,000

Two white wall-mounted electric heaters in a room with wood flooring.

2a. Hydronic fan coils

  • Quiet and responsive for heating and cooling.

  • Requires 120v power for the internal variable speed fan.

  • Can be mounted higher on wall or even ceiling.

  • Temperature control is via buttons on the emitters or hand-held thermostats.

  • $800 to $1200 (several sizes)

Two wall-mounted white radiators, one on a mint green wall and the other on a wood-paneled wall.

3. Air Handler (ducted)

A2W heat pumps can also be tied into ducted forced air systems using a hydronic (liquid-based) air handler for heating and cooling.  These systems use efficient variable speed fans (blowers) and can be fitted with air filtration systems and backup heating elements.

Arctic heat pump with insulated pipes in a utility room