Natural gas gets plenty hot. Also its the premier way to cook in my opinion. A natural gas stove is always better then electric cooktop. Electric ovens are another story. People argue that electric ovens are the way to go. Anyway, get a 95% furnace that runs on natural gas. You should probably spend the extra money and get a two-stage natural gas furnace. The high stage of the natural gas furnace would only run when extremely cold (like 15 F or less). It sounds like your in an area that doesn't get super hot. Where are you at? I would recommend getting a heatpump to replace any old air-conditioner while your doing this work. Heatpumps don't cost a fortune (like geo-thermal) does. And they do a great job of heating down to cool temperatures. You'll be able to heat your house with your heatpump down to 30. If your house is loose, you won't be able to heat down to 30 maybe more like 35. If its tight you will be able to heat down to 20. A heat pump shouldn't cost much more than regular AC. Most brands today have good warranty's. I have an off brand made by one of the the majors. Each company has less expensive brands. Trane makes American std. York makes Luxaire. Rheem makes ruud and etc. Hope this helps. I have a 90% gas furnace with 15seer 9.0 hspf heatpump. I control it all with honeywell focus pro kit. This model has an outdoor thermostat so you can automatically switch between the gas and heatpump based on outdoor temp.

thanks everyone for your input....has given me an idea of what I might expect. Would have done this several years ago, but could not find a contractor in the area who was doing remodeling....the new construction was so much more profitable and probably less problematic. Now that construction has slowed, I'm hoping I'll at least get some callbacks! Ron6519-thanks for straightening me out about how the separate structure doesn't save $ and hendricus..sounds like a great job you did - great to have those skills! Thanks all.

"Am I missing something?" In a word, yes. You're missing the knowledge that inferring the cost of a remodeling project based on the cost of new construction is an approach that can and often does lead to large errors. Even estimating the cost of new construction based on the cost/SF of a very similar home can lead to errors if the building site is different or market conditions have changed or the owner changes what they consider to be insignificant things that have a higher than insignificant cost. One cost benchmark is cost data for remodeling projects in the "Cost Vs. Value" Report published each year by Remodeling Magazine. They provide national, regional, and local costs for a variety of remodeling projects along with an estimate of how much the project adds to a home's resale value. The most recent year their report included the cost of a Family Room Addition was 2017. The cost they reported for a 16' x 25' mid-range quality addition with vinyl siding over a crawl space in the north/east Ohio market was $92,075. Here's a link: https://www.remodeling.hw.net/cost-vs-value/2017/east-north-central/cleveland-oh/ Add three years of construction cost inflation at say, 5% and you're at $106,600 +/- then add $8K to $10K +/- for a full basement with slab vs. crawl space foundation and the effort of cutting through the existing foundation and you're at $114,600 to $116,600--not too far removed from the $118,000 estimate you received from your remodeler. I don't think you're lacking for bids. I think you're lacking calibration with respect to real world remodeling costs in your market area.

In the 90’s, portable ceramic heaters were “high tech” and popular at the old cabin. I have two of those, as room heaters... I am planning to buy an Envi this fall for next winter. I have the old ceramics, but want to try something new. I am in CA, electricity is expensive. I want something to “keep the chill off” vs heating. I just wear a sweater.