Tell me about York furnace!

[trbomax]

This is my first post here.my son picked up 2 york 80k btu down flow furnaces at work for free. They worked fine,but they wanted an upgrade to 93% units. They were mfg in 1993. All the original books and paperwork are with them. My proposed use is in my newly built machine shop (on the farm).It is 1300 sq ft, insulated r-40 in cieling/r30 in walls. I will want to hold 40 degrees in there at all times during the winter because of electronics that are attached to the machinery. Humidity also cannot be an issue. The question is,are these "free" units worth bringing home for a look at them (they are 280 miles away,but I'm going there this w/e anyway) Or not? I had originally planned to install a 93% unit but figure I can by a lot of propane for the 2 grand it would cost to buy a new 93%.

[Dana]

Hot air furnaces are cheap enough and your heat load low enough at 40F interior temp that it's simply not worth the drive to pick up some oversized 17 year old "maybe". Your insulation levels are such that if it's reasonbly air-tight and glazed area minimal your mid-winter heat load at 40F interior temp probably won't break 25KBTU/hr even when it's -10F out. A brand new smallest-of-the line ~80-83% AFUE gas or propane hot air furnace is probably under a grand if you shop around, and even a small 30KBTU wall-furnace or radiant heater is probably enough to get you there.

Do a heat-loss calc on the place, figure out how much burner you need, and buy it. By the time a furnace is 20-25 years old you're looking at replacing contactors or motors in short years, possible corrosion issues with the heat exchangers, etc. They may or may not be worth repairing if they're already installed, it's freezing out, and you're desperate, but probably not worth re-commissioning in a new location.

If you like being actually comfortable in a 40F-50F shop room you might look for propane-fired radiant heaters mounted below the ceiling directed downward. Hot air furnaces suck from a creature comfort point of view, but ceiling mounted infrared is pretty decent. Gas models look like this:



Space-Ray (depicted above) and most other vendors make propane fired versions of their standard gas units. It's the right way to go in apps like this, IMHO.

[trbomax]

The 40-50 degrees is when we are not there. when we are working ,70 is about right.The shop is an insulated room inside the already insulated large shop. It is heated with forced air wood.The machine shop hes one wall that is "interior" ,it goes out to the large shop,but is still r-30.

[jimbo]

A furnace that old does not have that many years left. Is your install site such that downflow will be appropriate?

You have to look around for a thermostat that will give you a setting below the low 50's, but they are available.

The ultra high efficiency furnaces are more maintenance headache potentially, and they provide comfort features not important for your application. There is the fuel savings, though.

[Dana]

The 40-50 degrees is when we are not there. when we are working ,70 is about right.The shop is an insulated room inside the already insulated large shop. It is heated with forced air wood.The machine shop hes one wall that is "interior" ,it goes out to the large shop,but is still r-30.

With R30 walls you'd easily be able to heat the place to human-comfort temps with radiant heaters, and running them while the wood is bringing the place up to temp would also add to the overall comfort level. Design-temp for heating systems in your area is about -8F, which is only a ~50F delta-T from 40F. With R30 walls it doesn't take much of a burner to keep up- a standard 40 gallon hot water heater's output would likely be enough. If there's one in the building, a heat exchanger and sufficient baseboard that to deliver support a 50F delta-T on the building with 140F water would be enough for a freeze-control hydronic circuit.

Do a heat loss analysis on the building at both 50F delta-T & 80F delta. Any number in the middle is the amount of burner output you need. An 80K furnace is probably good down to -70F outdoor temps in a building like that.

[Lightwave]

Single stage equipment that can cope with -70 will have a big problem with short cycling in actual (i.e. down to -40) weather. That won't be good for efficiency, good for the remaining life of the furnaces, or good for comfort when the shop is occupied.

You'll need something with a low stage low enough that it that won't short cycle when holding an interior temperature of 40. A heat loss analysis is definitely in order.

Also, check your propane and electric costs on a per BTU basis. Propane has gone up so much in price over the past few years that it might be cheaper to heat with electricity.