Radiant heat using water heater or existing tankless water heater?

[Fsm09]

Hello everyone,

I’m hoping someone can help me here. I live in a smaller area where it’s hard to find a plumber that works on hydronic heating systems. I’m trying to heat the garage in order to help keep the bonus room above as well. The garage has r-10 foam under the concrete. There is a 4’ insulated foundation wall around the perimeter. I’m trying to see which option would be best for my situation. The garage is 850 sq ft

option 1 -would be use my tankless water heater which is 199k btu LP with a heat exchanger to heat the garage floor. I’m conflicted on this one because I see diagrams where they have hot and cold water connected together near the hot side of the heat exchanger. Also how would I disable the circ pump if someone was to take a shower or bath. Is disabling the circ pump even needed is the shower is being used. I may possibly need to add a baseboard heat in the bonus room later on as well. Only time will tell

Option 2 - I pick up a new/used 40 gallon hot water heat LP I was going to use to heat the garage. To me the heat exchanger on option one seems simpler. I would have to run another gas line and exhaust outside.

as of now I have 1 circ pump, 1zone relay, expansion tank. I guess I’m wondering do I need to make my connections out of copper or can I use pex? How critical is the size of line going in? Pex in the concrete is 1/2” oxygen barrier. I’m really hoping someone can help answer some of these. I appreciate any input.

 

[WorthFlorida]

I cannot answer most of your concerns on this subject as far a which heat source to use. However, you would want to probably go with three zones. One for the garage, one for the room above and the one for the house. Of course this adds considerable cost. You'll need a TACO controller and two additional circulation pumps. If you go with two zones, it almost be the same except one less circulator and thermostat. If the room above the garage needs a little heat but it's warm enough that the garage doesn't need heat, separate zone gives better flexibility and fuel savings.

One issue with heating a garage is freezing. If there is a failure of one of the heating plants, or you don't have the heat on and you get a quick freeze the water in the hydronic system can cause damage. Having WIFI thermostats is great for this if your away from home and there is a a sudden deep freeze. Many have programmed temperature warnings via e-mail.

What is needed to be known is, is the garage need to be a toasty workshop or keep it above freezing to store a vehicle? It's not mentioned but is there pipe in the concrete? If the garage needs to be used as an occasional workshop or when want to work on the car, electric baseboard may be a better option. Where would you install the 40 gal tank if you went in that direction?


https://www.supplyhouse.com/Taco-SR...QzL2rXDddmlBkY7Gt26fo4iOpJBWbiBQaAp3fEALw_wcB

 

[Sponsor]

 

[Fitter30]

Running DWH through the floor is a bad idea. How many feet of tubing do you have in the slab?

 

[Fsm09]

I cannot answer most of your concerns on this subject as far a which heat source to use. However, you would want to probably go with three zones. One for the garage, one for the room above and the one for the house. Of course this adds considerable cost. You'll need a TACO controller and two additional circulation pumps. If you go with two zones, it almost be the same except one less circulator and thermostat. If the room above the garage needs a little heat but it's warm enough that the garage doesn't need heat, separate zone gives better flexibility and fuel savings.

One issue with heating a garage is freezing. If there is a failure of one of the heating plants, or you don't have the heat on and you get a quick freeze the water in the hydronic system can cause damage. Having WIFI thermostats is great for this if your away from home and there is a a sudden deep freeze. Many have programmed temperature warnings via e-mail.

What is needed to be known is, is the garage need to be a toasty workshop or keep it above freezing to store a vehicle? It's not mentioned but is there pipe in the concrete? If the garage needs to be used as an occasional workshop or when want to work on the car, electric baseboard may be a better option. Where would you install the 40 gal tank if you went in that direction?


https://www.supplyhouse.com/Taco-SR...QzL2rXDddmlBkY7Gt26fo4iOpJBWbiBQaAp3fEALw_wcB

thanks for the reply. We just finished building the house. The main house has forced air with AC. The bonus room above the garage doesn’t stay as warm as it should. The HVAC guys are dragging their feet on adding more airflow in the bonus room. My hope is heating the garage will help keep the room above warmer. The garage will be around 55-60 degrees in the winter time. It is 28x28 with an 8x8 gun room off to the side. I would likely get the water heater in the 8x8 room. The tankless heater is about 15’ from the garage in the laundry. I have a 4’ crawl space so adding more water line isn’t an issue. The reason for added heat upstairs is just another way to help warm it up. In zero degree weather the bonus room currently sits about 15 degrees cooler than the main house. I figured I would use glycol similar to what my shop currently has for heat. The plumbers that did the hydronic heat in my shop retired so I can’t have them do the house for me.

 

[Fsm09]

Running DWH through the floor is a bad idea. How many feet of tubing do you have in the slab?

Just under 800’ 1/2” oxygen barrier pex

 

[Jadnashua]

Is that 800' just one big loop? Most of the time, they suggest the maximum single loop length of around 200', but all of them could be on the same zone, you'd just feed them all with a manifold. At 800', the water by the time it got to the end would not keep things even as it would have cooled down too much. There's also a limit on how hot you can make the water going in.

One thing to keep in mind, it can take a long time to stabilize the temperature of a cement slab, so don't expect to use a setback, and then want the area to get warm like can happen with say forced air or even radiators...it could take literally days to bring it up to temperature, depending on how cold soaked it was and how thick.

 

[Fsm09]

Is that 800' just one big loop? Most of the time, they suggest the maximum single loop length of around 200', but all of them could be on the same zone, you'd just feed them all with a manifold. At 800', the water by the time it got to the end would not keep things even as it would have cooled down too much. There's also a limit on how hot you can make the water going in.

One thing to keep in mind, it can take a long time to stabilize the temperature of a cement slab, so don't expect to use a setback, and then want the area to get warm like can happen with say forced air or even radiators...it could take literally days to bring it up to temperature, depending on how cold soaked it was and how thick.

the longest loop is 300’. So I have 2 300’ coils and around 200’ of the third coil

 

[Fitter30]

800' pex = 27000 btu's 3 gpm @11.4 ' head 30% propylene glycol