We had a WaterFurnace NDZ038B14AC installed last November, using the existing gas furnace for backup. I'm happy with it -- it keeps the house warm, mostly runs on stage 1, and has not once gone to the gas backup. I got geo to get off of fossil fuels: mission accomplished.
However... I did not expect that our heating costs would go up. Of course gas prices are ridiculously low. So I went back to the GeoLink Design Studio report from our contractor. It predicted a cost of $944 for heating with gas, $739 with geo. At prices of $1.2/ccf and and $.13/kwh, that says we would be using 7.3 kWh/ccf.
Taking out non-geo electric use, our 3 bills since install show us using .95 kWh per degree day. Last year on gas we used .085 ccf/degree day. This gives a pre/post install ratio of about 11 kWh/ ccf.
It seems we're using 50% more electricity than GeoLink predicted. Is this normal? Anyone else have experience converting from natural gas to geo?
Some more info... We live near Milwaukee WI (53213) in a 1500sf Cape Cod, well sealed and insulated. GeoLink design was for a 40,000 Bthu heating load. It's a Waterfurnace NDZ038B14AC split system with desuperheater, buffer tank to electric water heater (old gas heater used as the buffer tank). Gas blower/ backup furnace is a 96% efficient York Affinity. 3 vertical loops, each 180', about 12' apart. Installer added a large return grate in the basement return air manifold, but no other duct changes.
The first full month on geo (November) we used 883 kWh, of which I attribute 743 to geo + hot water. The prior year on gas we used 70ccf gas, but it was a bit colder. Next 2 months were colder but similar ratios. We use very little hot water (last summer we used about 4 ccf/ month, cooking and hot water). Our installer's worksheet shows 53.2 degree EWT, 47.2 LWT, 60 degree EAT, 92 degree LAT. Just now on stage 1 I measured 66 degree EAT, 81 LAT (I assume it was stage 2 when installer measured). Last year on gas we set back the thermostat during the days and overnight. This year we leave it constant (69).
Our installer (Mark Doll, Professional Geothermal) was careful and attentive. He re-did the initial GeoLink analysis with more current gas prices, but it's the ratio of geo kWh to pre-geo ccf I'm interested in, and that did not change.