OT, small gas furnaces

surplusjohn · Dec 30, 2019

my Girlfriend owns a small art gallery and frame shop [Edgewood Gallery in Syracuse] and we need to start thinking about replacing the furnace. [a few years ago she installed a split phase AC and is super happy with it]. Currently there is a 60K BTU, 40 year old, conventional gas furnace, which is probably oversized. the space is made up of two adjoining rooms, a 20 x 20 gallery space and a similar work space where she spends most of her time. The furnace is in the work space with a single duct to the gallery space. Space is at a premium so I am thinking that the 4 x 6 foot space that the current furnace is currently occupying can be freed up by going to a compact wall or ceiling mounted unit, but we would still need to be able to connect to the duct for the front room.
so, natural gas, roof stack, 60k BTU, super compact, both direct and ducted, any ideas on what to look at? I am pretty sure the town does not allow un-vented units.

gustafson · Dec 30, 2019

HOw many square feet is the space?

Mini split heat pumps take up but a little wall space and best one work for heat well into the negative numbers

If you stay with gas, efficient gas furnaces do take up space, I have a pair of 90 percent efficient ~20 year old jobs hanging on the wall here at work. The are around 2x3x5

Bill D · Dec 30, 2019

California and other states have outlawed ventless furnaces. So good choice there. California also requires a CO monitor be installed NOW in all dwellings not just when the property is sold.
But gas stoves have no cooking oven chimney connections of any kind unlike decades ago.
People say do not buy the super efficient furnace but stay one step down for more reliabilty. That old furnace is probably about 50% efficient replace it with a 85% efficient unit. The new unit will also not have open chimney venting heat all the time.
Bil lD

deltap · Dec 30, 2019

Furnace size depends on insulation levels and building tightness. 800 sq ft with good insulation should be ok for 40mbh 90+ furnace. Horizontal hanging models are available if space is at a premium. Ok to get ideas here but you really need a professional to do it right.

DDoug · Dec 30, 2019

Look at the intended furnace and see if it can be configured "attic horizontal"

Instead of trying to find a Hi-efficiency reznor type hanging furnace.

surplusjohn · Dec 30, 2019

thanks for info, I am just looking for ideas, I wont be installing myself.

surplusjohn · Dec 30, 2019

I was thinking that a Reznor type could not be ducted, also noisy?

neilho · Dec 30, 2019

A minisplit takes up no floor space atall...

But, they work only wit' juice and at the very best, into the negative numbers. About as efficient as straight resistance electric below 10degF. Yuk. Mitsubishi makes some of the better units.

Back it up with a small woodstove or pellet stove for really cold spells and power outages. Some sheetmetal and a fan can mate up with the existing ductwork to the gallery. 4x6 floorspace is plenty big for that.

My $.02.

DDoug · Dec 30, 2019

surplusjohn said:
I was thinking that a Reznor type could not be ducted, also noisy?

IIRC they now make them in the PVC in/out piping hi eff models.

But they are much more money than just buying a standard house model hi eff furnace, and setting it up for attic/crawlspace usage (horizontal)

gustafson · Dec 31, 2019

neilho said:
A minisplit takes up no floor space atall...

But, they work only wit' juice and at the very best, into the negative numbers. About as efficient as straight resistance electric below 10degF. Yuk. Mitsubishi makes some of the better units.

Back it up with a small woodstove or pellet stove for really cold spells and power outages. Some sheetmetal and a fan can mate up with the existing ductwork to the gallery. 4x6 floorspace is plenty big for that.

My $.02.

This is not true. Newer types, 'hyper heat' being one, will work to 15 below and beyond, and at decent efficiency

Most furnaces won't work in a power outage anyway, but you would need a big generator to run a heat pump

gustafson · Dec 31, 2019

Bill D;3466255 People say do not buy the super efficient furnace but stay one step down for more reliabilty. [/QUOTE said:
My shop has 2 Honeywell condensing hot air furnaces, PVC in and out, installed, probably late 90's

I have been there since 2003.

Replaced one glow element, and one pressure switch between the two

I will take 17 years of lower gas bills for 100 bucks in parts all day

There is, as I understand it, a difference between the ~92 percent and the ~96 percent, in that in order to get that last bit of efficiency the stainless steel is actually thinner. that may affect longevity, but I have no personal experience with that

snowman · Dec 31, 2019

Find your local independently owned HVAC supply warehouse. Ask them.

They'll be able to give you the most informed viewpoint of what holds up, what continues to have parts available, and generally have a better opinion than the local install guy who likely has gotten comfortable with one brand.

One thing they stressed to me is that I shouldn't buy it online...they didn't care if I bought it from them, but online sellers may not qualify for warranty, no matter what they say.

And if you go to 90%, just make sure you have a way to deal with the water. I've got a 90% in my garage, works great...but the damn thing gives off 5 gallons of water a day when it's really cold out, and not having a drain nearby means I have to remember to dump a 5 gallon bucket.

surplusjohn · Dec 31, 2019

this is a commercial building, no attic or crawl space, block building with concrete floor and flat roof. it gets cold around here, sometimes 3 weeks of below zero. heating season from October to May not as cold as it used to be. she already has a slit phase for ac and heat until November early December. figure 20 x 40 overall size with minimal ceiling insulation. drop ceilings at 8 foot.
present furnace is adequate and still functioning at maybe 40 years old. When she started there 30 years ago, it was existing, just thinking ahead. the recovered floor space is a bonus as well as lower gas consumption.

neilho · Jan 1, 2020

gustafson said:
This is not true. Newer types, 'hyper heat' being one, will work to 15 below and beyond, and at decent efficiency...

You're right, they're better than I thought. See https://www.nrel.gov/docs/fy11osti/52175.pdf if interested. Tests didn't go below -10F, COP at 2.

Since she already has one, prob a moot point.

Sounds like more insulation could be helpful, though that's not really the focus of the thread.

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