In the last post on the geothermal heating system home project, we found an installer and financing.  Ever forward to.....duct decisions!  Trust me, since it affects interior aesthetics, you're going to want to get this right...or your spouse will want you to get it right. 

Duct Alignment, June

In June, I have discussions with the engineer, Damien, about how and where to run the heating ducts. Because currently we have no central heating, we have no way to circulate warm (or cold) air. Forced air is the most practical option with a geothermal heat pump; baseboard heat with a water circulation system would need much hotter water than a normal heat pump generates. If you designed a heat pump to deliver that temperature, its efficiency -- the advantage it offers over plain electric heat -- would drop substantially. (Heat pump efficiency for heating is called "coefficient of performance", or COP.) Radiant heat from tubing in the floor is possible.

If you already have central air conditioning, your existing ductwork should be okay; if you have only forced-air heat, your ductwork may be too small and at least parts of it will need replacing. It is not uncommon, however, to find conventionally heated, forced-air systems that are overdesigned (able to deliver more air than necessary), so you may be OK. Your engineer must examine what you have and do the calculations. If you have baseboard steam or hot water, you must get ductwork installed. Duct size is important, as the heat flow carried by the air must match the heat flow the heat pump maintains to or from the external loop. Undersized ducts can result in air conditioning freezeup on hot days or simply inadequate heating or cooling.

On a new construction job, you can easily build in the ducts, but we have to give some thought to the route they will take. The first floor will be served from ducts in the basement. The second floor from ducts in the attic. But how do we get the conditioned air to the attic from the basement, without having that duct take up valuable floor space or look weird? We consider a tortuous route through our bedroom walk-in closet, which has the benefit of being hidden from general view, but which seriously cuts up the closet space and adds complex angles. Ultimately, we find a corner of the dining room and my upstairs office that's not in the way, so the two main ducts (one for air out, one for air return) to the attic can be run side-by-side all the way.

Permits and setbacks and well sites... July!

Before any work really began, we had to ensure that any permits were in hand. We had a permit from the state Department of Environmental Protection, to begin with.  Work near or in wetlands in our state has to get permission from the town's Conservation Commission, but we were far from any wetlands, being basically on a high, dry cliff. Finally, we had to run the plan past the Board of Health; not that there was really much reason for them to be involved, apart from distance from the drinking well and septic system. We're not pumping any water out, except during drilling, and the external loop of pipe running through the wells contains only food-quality propylene glycol and water so there is no risk of contamination in some catastrophic event.  (The pipe is also separated from the earth by a fairly impervious grout, packed into the hole, around the pipe.)

It was good that we did check with the local authorities, though, because they told us that a 25' setback was required from the property line. Our engineer had initially assumed a 10' setback, and we had planned to have them close to that limit in order to allow any future expansion of the house in that direction.

After many tape measurements by me and the contractor, we established the locations for the two 320' deep wells, more than 50' from the drinking well, more than 25' from the property line, and more than 20' apart from each other.

An initial inspection by the well driller showed that the drilling rig would need a short temporary road lightly bulldozed through a rise at the side of the driveway and some leveling down nearer the drill sites. The rig is about 30' long, with maybe 8-10" of clearance underneath, so crossing any little hill ran the risk of hanging up the undercarriage. We determined that passing under the utility lines would be OK if someone held up the wires. The road was not in the original plans, but... hey, we're on a fixed price contract.

To be continued...