Converting Closed Radiant BBoard to Potable HW

tc60045

Gang,



I currently have a small, supplemental baseboard radiant system in our basement. House is heated by forced air; this system makes basement usable for the kids. System runs at 140 degrees, but I can goose it to 180 if need be.



Debating going to a condensing water storage heater that will handle duties of DHW and this small, radiant system. That is another thread...



If and when I do move to such a heat source, I'll be getting rid of a closed system and using potable hot water in this loop.



Can anyone point me to the steps I should follow to clean out the radiant pipes and make this transition? Example: drain, re-fill and run at 180 for a week, then turn off heat, add x gallons of bleach per y feet of tube. recirc an hour a day for a week. (I'm just making this up..... What are the REAL steps, please ! )



This system was well-designed, with anti-backflow valve, air purge valve, pressure gauges, pressure bladder, etc. Haven't drained it ever, on plumber's advice to "leave it be."



Many thanks,



TC

Gordy

Separate DHW

With a heat exchanger keeping the BB loop a closed system. Then the circulator, and any other ferrous components will not have to be changed to bronze, or SS.

Charlie from wmass

You will rot out the baseboard

or cross contaminate the DHW. use a Heat exchanger, you families life is worth more then it costs I can promise you that.

Gordy

One other thing

If you need 180 for the baseboards I doubt a condensing WH will get it done maybe 160 plus losses from the heat exchanger you should use.

tc60045

Thanks

Gordy and Charlie -- thank you both for your replies.



Can you guys point me to a heat exchanger suitable for this application? I'm a little confused as to what one looks like as my googling of "heat exchanger hydronic" has brought back everything from brazed plate heat exchangers (how the heck does that attach, and where) to solar heat exchangers, etc. Thanks.



Since we keep our DHW at 125, I'm not sure how I'll be able to step the heat up from 125 to the 140 we've been using for our BB system, but perhaps that will be more clear after I research what you send.



I've found two condensing WHs that could handle both DHW and a close hydronic system. The HTP Versa something with a solar option, which keeps a separate coil at the bottom that could be used by a closed BB system, and the Triangle Challenger, which is more akin to a tankless, but can handle both, too. Any others I should be considering (again, this may rely on me reading up on heat exchangers, first).

Ironman

Taco X Pump Block

It has everything as far as heat ex. pumps, outdoor reset. Not cheap, though, and limited to about 50k btu's. You'll still need all the ancillary components: fill/backflow, relief valve, expansion tank, gauge, air separator, etc. See attachment.



A combi boiler is your other low end option: Bosch, Navien, Cadet and the T.T. Challenger which you mentioned are a few.



As pointed out, please do Not try to connect the hydronic directly to your potable system: it's strictly forbidden by code and a serious health risk to your family. Open hydronic system are also a bad idea that can develop serious issues with time, not to mention the risk of Legionella.



Depending on the load, you may have to run the water heater at 160*+ to get the btu's you need if you use the X pump block and a water heater (see the chart in the instructions). Then you'll need a tempering valve on the domestic side. You may have to use something other than pvc for venting at those temps, too.



Do you know the hydronic load? How many lineal feet of baseboard element?

tc60045

Great - thank you

Great stuff, Ironman -- thank you.



Excellent documentation on that product -- doing the math, looks like at the 7.5GPM limit of the product you mention, I can get 30,000 BTUs from an 8 degree temperature delta, which is great. May have to step up the DHW temperature, as you mention, but I'll do some testing with BB performance at lower HW temps in these few days of winter left and see.



To all who replied, you saved me from considering doing something illegal and dumb, you pointed me in the right direction, and gave me homework to do so that I better understand what I need when I do get new equipment. Thank you very, very much.



TC

Ironman

Glad to Help

A 20* Delta T is the normal design for B.B. Lower won't hurt anything and may give a little more even output from first to last rad.