New gas furnace for big old house
Greetings, and thank you in advance for your assistance.
We own a pretty big 1901 "Princess Anne" (late Victorian) single family, about 3800 sq ft if you include the very unfinished basement, close to 3000 for the 3 living floors, high ceilings, lots of windows. We currently have a 10 year old, 148,500 BTU, 85% oil furnace. 10 years ago I myself ran a heat loss program, carefully measuring and entering every detail, and came up with 127,000.
We would like to replace our system with natural gas, which is already coming into the house for our water heater and cooktop only. We live in New England and heating with oil has become horrendously expensive. We would like, ideally, a highly efficient (at least 95%) direct vent, two stage, variable speed system.
Cost is NOT the issue. Two problems, for which I am requesting advice:
First of all, efficient gas furnaces simply do not come as big as oil furnaces. We have gotten several estimates, and nobody seems to know what to do about this. The alternatives seem to be either a 133,000 BTU single stage, non-variable-speed system, OR a 120,000 BTU variable speed 2 stage system, which appears to be as big as they come. Those who recommend the latter insist it will be big enough, due to high efficiency. I just don't know. Which would you do? Any alternatives? (I know there is also the possibility of twinning two smaller furnaces, but if I am not mistaken that precludes the variable speed option anyway - so might as well just get the 133,000 single stage - right?)
One reason I really want the variable speed motor is that I think it will heat my house more evenly. The upstairs never gets as warm as the first floor, which is where the thermostat is. The system comes on full speed, warms up the foyer and the thermostat turns off the system. I think variable speed would help.
Second problem, which wasn't mentioned by anyone until the 4th estimate: presently our furnace and water heater vent into the chimney. I am now told that removing the new direct-vent furnace from the chimney will necessitate either a new expensive chimney liner for the water heater, OR a new power-vented water heater (it may be a problem to find a good place to vent it). The water heater is very old and we don't mind replacing it, but I'm not sure what steps we have to take and why the first several contractors failed to mention this. (We have been told lining the chimney for a regular water heater will cost several hundred dollars - or several thousand!)
Thank you again for any guidance on these two issues.