More OWB questions

[nwmo_aggie]

Still working on plans. Think I’ve settled on a Heatmaster SS, but local dealer doesn’t do any installs, so I’m trying to figure out some of this on my own.

Backstory...I have a small house (900 sq ft main level, 900 sq ft basement) currently heated with a freestanding wood stove, burning ~4 cords of wood annually. I’m looking at adding on another 900 sq ft on a slab with radiant heat in the floor. I’d like to use a C150 for this application, it seems like it has adequate capacity for my needs, though I may not get up to the 12 hr burn times some get. I’m not too worried about that, someone is here most all time.

It’s 60’ from where I’d like to place the C150 to where the lines will enter the house near my central air/LP furnace. From there it’s another 16’ across the basement to where the manifold for the radiant heat would be. Can I run the water through the forced air heat exchanger, then to the radiant floor and back to the stove? What additional parts will I need? Dealer did say they set all stoves up with a heat exchanger for the floor heat, I’ve seen some circulate stove water in the floor...I guess his way is OK?

 

[NSMaple1]

I would likely use a HX.

 

[nwmo_aggie]

I would likely use a HX.

Thanks. Will do that for the floor heat.

Is it feasible to route the water through the forced air heat element, then to the floor? If I understood what he was telling me correctly, he thought I’d need another pump. Essentially make a loop to the forced air, and tee off that line ahead of the forced air plenum, add a pump and pump water to the floor heat and back.

 

[rancher2]

I would run two sets of lines to the house one for the forced air element and one for the floor heat. I would use a HX for the floor heat and use antifreeze with a pressure tank on the floor side of the HX. If you wanted to save some money you could use the return water out of the forced air element to heat the HX floor heat. The water running to the floor heat doesn't need to be nearly as hot as for the forced air element. Make sure you put the biggest element in the duct work as you can. If you are handy you could do the install work your self. When I put my Garn in 10 years ago I did all the install other than the spray foam work.

 

[NSMaple1]

Thanks. Will do that for the floor heat.

Is it feasible to route the water through the forced air heat element, then to the floor? If I understood what he was telling me correctly, he thought I’d need another pump. Essentially make a loop to the forced air, and tee off that line ahead of the forced air plenum, add a pump and pump water to the floor heat and back.

There are different ways you can do this.

Is your OWB loop going to run 24/7? If so, I think I would run that to the forced air HX, then through a flat plate HX, then back to the OWB. The other side of the flat plate would be all the infloor stuff, with a mixing valve and a second circulator. The second circ would run on demand via a controller on the floor side. You want the in-floor water to be a constant temperature - and usually not any much more than 100f or so. Which is where/why you need to be careful heating a floor with an OWB.

The OWB side of the flat plate would be unpressurized, the floor side of it would be pressurized. That's how I would do it, I think.

 

[nwmo_aggie]

There are different ways you can do this.

Is your OWB loop going to run 24/7? If so, I think I would run that to the forced air HX, then through a flat plate HX, then back to the OWB. The other side of the flat plate would be all the infloor stuff, with a mixing valve and a second circulator. The second circ would run on demand via a controller on the floor side. You want the in-floor water to be a constant temperature - and usually not any much more than 100f or so. Which is where/why you need to be careful heating a floor with an OWB.

The OWB side of the flat plate would be unpressurized, the floor side of it would be pressurized. That's how I would do it, I think.

That’s sort of what I had in mind. Is having the owb loop run all the time acceptable?

Since there will be 3 rooms in the addition with the floor heat, do I run 3 thermostats and some sort of valves, or just run it as 1 like you’d do with normal forced air?

 

[rancher2]

Its not a lot more work when you pour the floor to set the tubes up so you would have a zone for each room so you can control the temp of each room. I would set it up with three zones and three thermostats. You can let the water coming from the OWB run all the time and turn the pump on and off with the thermostats in each room on the floor heat side of the HX. You will have another thermostat set up to run the blower in the furnace to heat that part.

 

[nwmo_aggie]

Its not a lot more work when you pour the floor to set the tubes up so you would have a zone for each room so you can control the temp of each room. I would set it up with three zones and three thermostats. You can let the water coming from the OWB run all the time and turn the pump on and off with the thermostats in each room on the floor heat side of the HX. You will have another thermostat set up to run the blower in the furnace to heat that part.

Does that require 3 pumps on the floor heat side, or one and some sort of automatic valves to control which section gets heat?

 

[NSMaple1]

I don't have floor heat so no direct experience, but I think you should be able to control each zone with it's own thermostat and zone valve, and use one variable speed circulator for all, with a manifold setup. I have a Grundfos Alpha circulator for my 4 zone baseboard system, it is a great circ. It automatically speeds up as more zones open - maintains a constant dP (pressure differential across inlet/outlet). I am just not sure the effect that a mixing valve would have on a setup like that.

 

[bowtechmadman]

I have zone valves with my circulating pump running those zones doesn't shut off. My pump also runs constant from the stove to the HX. I run strictly hot water so can't speak to the air to air exchanger but I'd guess you can run to that exchanger prior to the water/water exchanger. Agreed put in zones for all rooms that you are adding the in-floor heat.

 

[rancher2]

Does that require 3 pumps on the floor heat side, or one and some sort of automatic valves to control which section gets heat?

One pump should handle the three zones. You will have to install some relays so the thermostats will control that pump. You don't want that pump dead heading when no zones are calling for heat. You will probably be able to get by with one mixing valve ahead your floor heat manifolds.

 

[NSMaple1]

One pump should handle the three zones. You will have to install some relays so the thermostats will control that pump. You don't want that pump dead heading when no zones are calling for heat. You will probably be able to get by with one mixing valve ahead your floor heat manifolds.

That's a good thing about Alphas. When in dP mode, if they get dead headed, they just stop. Then start again when the restriction is removed.