First time posting here and I have searched a little for ideas. Currently I have a 30' x 70' shop that is heated with floor radiant (hot water/PEX in the concrete floor slab). Hot water is provided by an outdoor wood furnace that also heats my home and domestic hot water. My need to use the shop are now minimal and it takes a good bit of wood just to knock the chill off the entire shop. I will be draining the system in the floor to prevent freezing but wish to use the shop on occasion. I was thinking of utilizing an old HVAC unit that I have on hand as a water to air heat exchanger so that I can quickly heat with forced air on demand. I would simply hang a double row of tarp from the ceiling across the width of the shop, isolating area of about 30' x 20' to heat. This should work fine and heat the area quickly when needed. My concern is freezing of the HVAC unit when not in use. I was thinking of well insulating the unit and placing a small electric heat source within the enclosure to keep it above freezing. Any ideas about what components of the old HVAC unit to use and setting up controls would be appreciated.
Using an old HVAC unit for heat exchanger
- Thread starter slmiii
- Start date
Jim greengo
Well-known member
What are you going to use for a coil?
nsula_country
Well-known member
What type of "HVAC unit" are we working with?
CT
CT
I planned on repurposing the unit and sweating some PEX fittings on to circulate the 180-degree water from my wood furnace instead of refrigerant through it. It may only be an A/C unit, but I think it has the air-handling stuff in the enclosure. The unit was given to me a long time ago and I haven't looked at it in several years. I really need to see what I have to ask more intelligent questions I guess.
Milton Shaw
Well-known member
- Joined
- Feb 11, 2011
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Normally the diameter of the lines is going to be too small to get much water circulation and heat exchange. Most lines would be 3/8 or smaller and would require quite a bit of work to re-plumb the fittings to the same size instead of the smaller cap tubes you probably have now. An old heater/core from a bus or RV would be a better choice than an A/C coil would ever be. Even a small radiator with fan from a small car would do a better job.
Jim greengo
Well-known member
If you could find an old coil from a pump/dump system that wasn't rotted out that would probably be your best beat.
PWC Repair
Well-known member
Hey.....there's a Youtube vid for that!
Fill it with propylene Glycol and it won't freeze, problem solved.
LS6 Tommy
Well-known member
A Direct Expansion cooling coil repurposed for hot water heat won't work well at all. The tubing is too small. You can have a proper hot water coil made, but you won't like the price...
Tommy
Tommy
75gmck25
Well-known member
If your work in the shop is very infrequent, I think I would look around for a used gas or propane radiant heater that mounts in the shop, and just use it when needed. The gas/propane heater will take the chill off much faster than trying to bring up the room temperature using hydonic heat in the slab.
Even if you don't have propane in the house, and have to run it off small propane tanks, it probably won't use that much fuel if you don't use the shop often.
Hyrdonic in the slab is great for heat, but not the best choice for infrequent use in a freezing climate.
Bruce
Even if you don't have propane in the house, and have to run it off small propane tanks, it probably won't use that much fuel if you don't use the shop often.
Hyrdonic in the slab is great for heat, but not the best choice for infrequent use in a freezing climate.
Bruce
nsula_country
Well-known member
Are you are describing an air handler (cabinet with a blower) with an A/C coil in it?
If this is correct, are you describing that you would like to flow heated water through the coil and use the blower to create a hot water forced air furnace?
CT
The "coil" in the OP's unit sounds like a typical AC evaporator -- not going to work. He needs a hydronic coil ...maybe able to finds a used one. Better luck finding a used commercial hydronic fan coil heater -- they look like a hanging garage heater except have a coil for hot water vs a gas burner.
nsula_country
Well-known member
I was not thinking that the evap coil was going to work well either. Capillary tubes, TXV, Piston, ect. And a lot of 3/8" tubing, pretty restrictive for liquid flow. I have zero experience with hydronic heating. Only industrial steam coils used in wood presses and industrial parts washers.
Though I give a pass for the creative thinking!
CT
TractorJeff
Well-known member
A guy I know in Illinois has an old 1920's(?) Mack radiator with a box fan in his shop for hot water from his outdoor woodstove. Heats the whole 30 by 50 semi insulated shop with ease!
Its the "Cool" factor!
Its the "Cool" factor!
PWC Repair
Well-known member
There's actually a Youtube vid for that too! Guy shows how to cut off the ends and repipe small tubes to a larger common tube for flow.
bobbyjean
Well-known member
wow-electric to keep it from freezing...you guy's must have low kw costs down there
whatever setup you go with i would add glycol...maybe 40% by volume
whatever setup you go with i would add glycol...maybe 40% by volume
nsula_country
Well-known member
For some of us, electric is the only choice. Unless we set up LPG service. And depending on providers, that can be a pain in the **** too.
CT