OT: steam and hot water heat

[stovepipe?]

sorry for the non-wood-burning nature of this question (sort of wood burning related since it is about back-up heat to a wood stove) but can't help but avail myself of the collective knowledge of this forum.

I want to heat a part of the house that wasn't previously heated. I have a steam boiler and steam heat in the house. I was thinking I would simply set up hot water heat for this room-- a circulator controlled by a thermostat in the room. my boiler produces domestic hot water, so I'd simple run off of that to a circulator, through radiator and back. Is there any problem with this-- i.e. with returning domestic water that's run through a circulator/radiator back to the domestic water supply?

 

[elkimmeg]

why not add a zone of steam heat. keep it simple

 

[stovepipe?]

that would actually be much more complicated since it would be very difficult to balance it/ set up the return. Hot water would mean the gravity issue would not enter the picture-- piping can go up, down and around no problem. also, I want to be able to control it as a separate zone on a separate thermostat.

 

[Sundeep Arole]

The one issue with your idea is that you would have to use a circulator suitaible for potable water - a bronze instead of cast iron one. Adds a little more expense, but AFAIK, it is doable. Mind you, I'm no expert in this matter, just a homeowner who just got interested in this recently and read up a text on hydronic hot water heating systems so I could muck with my own.

 

[elkimmeg]

With anti scald codes hot water is about 119 degrees, baseboard heat requires160 but even better 180. modern hot water heaters max out 140 and will not recover or deliver the vollume or heat range required to be effective even if they did what happens when the demand from the termo and hot water fawset is at the same time?? Craig knows of one Hotwater heater designed to handle the job but your common one will not

 

[zogboy]

Have you thought about tapping into domestic coil? You will need to zone it separate from the HW tank as running that will over heat the tank.
A couple of motor valves and a t-state and 8’ of fin tube for the room and your in business.

 

[stovepipe?]

hot water comes off of the boiler-- tankless coil. the boiler keeps it at 180. a mixer keeps the water in the pipes at 120. for heating purposes I would cut in between the coil and mixer, hot going out, return to cold in. so the water to the radiator would be 180- hot enough to heat no problem. the ONLY question I have, partially answered above, is whether water that passes through the circulator and radiator remains potable since it will be returned to the general domestic supply. do I need some particular type of radiator? cast iron ok or no?

 

[Sundeep Arole]

hot water comes off of the boiler-- tankless coil. the boiler keeps it at 180. a mixer keeps the water in the pipes at 120. for heating purposes I would cut in between the coil and mixer, hot going out, return to cold in. so the water to the radiator would be 180- hot enough to heat no problem. the ONLY question I have, partially answered above, is whether water that passes through the circulator and radiator remains potable since it will be returned to the general domestic supply. do I need some particular type of radiator? cast iron ok or no?

From what I understand cast iron is NOT ok for this kind of application. Copper or Brass/Bronze.

 

[Eric Johnson]

Normally, a cast iron radiator would work fine. But since this is domestic water, it contains oxygen and will corrode the radiator. I don't know if household water pressure is too high for the fin & tube baseboard and the circulator. Might be an issue. Personally, I would try to rig up a heat exchanger and run a closed loop, pressurized zone for that room, but then you're getting into pressure tanks and PRVs and a bunch of other hardware that's going to run the bill up. I'd do that because I think it would be fun and because I would want to use a cast iron rad.

Assuming pressure is not a problem, then why not run the water through the coil in the boiler, then through the baseboard, and then into the hot water heater? I think that would work just fine. HotFlame is right about cast iron vs. bronze circulator construction, although I ran a Taco 007 cast iron circulator for about 10 years between my water heater and a coil in my boiler, and it ran fine the whole time. Either way, you'll pay about half of retail for a new circulator if you buy it on Ebay.

 

[elkimmeg]

You did not say what GPM your hot water coil is rated at. Other things to consider now a thermo is controling your hot water demand
Don'r get me wrong it is do able. Eric brought aout a good point about pressure you will have to reduce it to 15 lbs +- That could be as simple as partically opening a ball valve on the feed side Part of the ppressure issue is allowing the heated water to pass threw the radiators to discharge also to allow heating up the water too you would push threw less heated water it it does not remain in the coil long enough

 

[stovepipe?]

5 gpm. this would be for a single radiator heating a 150 sq ft room in which a wood stove would do most of the heating anyway. so I think supply would be ok. how does a setup w/ a water heater circulating to a coil in the boiler work? to give a free boost to the water heater during the winter?

 

[Eric Johnson]

I have a different arrangement now (still heat my hot water with wood, though), but at the time I had a coil in my wood-fired boiler and I circulated water between the water heater and the coil. That gave us an unlimited amount of free hot water (for the cost of running a Taco 007 circulator) and served as a heat sink for the boiler as well. It worked great. I had it set up so that an aquastat in the boiler would turn the circulator on when the boiler temp hit 140. Therefore even on cold mornings when the boiler had burned down overnight, we still had a tank full of at least 140 degree water. I'd flip the breaker for the electric elements in the fall and turn it back on in the spring.