# Hydronic System Heat Exchangers

• posted on January 10, 2010, 3:04 pm

I'm new here but wish I had found this site long ago. I have designed and built an in floor hydronic heating system for a new home I'm building in Ontario cottage country. Because we are located where natural gas is not available one of the aims of the new system is to take advantage of low rate electricity offered by the Smart Meter System soon to launched in Ontario. I am using a Monitron EH25 electric boiler to heat a 1000 gallon tank of water which will be my energy reservior. The boiler, through a closed circuit with a heat exchanger, heats the tank of water up to 180F at night when the power costs about 5.2c/ kWh. For a heat exchanger I'm using a modified automotive radiator situated in the bottom of the tank. This much is completed and works just fine. The heat loss calculation for the house indicates that the maximum heat loss to be around 60,000 BTU/hr. I have built most of the 2 manifold distribution system with 4 zones of 250 feet on each mainfold but am still trying to figure out how large a heat exchanger I will need for the heat distribution side of the system, this will also be a modified automotive radiator. Anyone have a calculation as to how many square inches of a copper water to water heat exchanger will be required to extract 60,000 BTU/hr and deliver an output temperature about 20 degrees cooler than the tank temperature?
------------------------------------- Magicare

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• posted on January 10, 2010, 9:57 pm
On Jan 10, 9:04 am, michaelsalter_at_gmail_dot snipped-for-privacy@foo.com (Magicare) wrote:

You are going to attempt to put 160f in a radiant system designed for 110-115, so its cooked dead pets, ruined floors, hot shoes and feet. www.heatinghelp.com is where there are all boiler pros, post at "The Wall". There is some type of thermostat manifold where you will be able to use the tank water with no exchanger and it will mix in return feed for a 110 floor water temp. I think you should re evaluate it all with a heat pro.

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• posted on January 11, 2010, 7:55 pm
magicare had written this in response to http://www.thestuccocompany.com/maintenance/Re-Hydronic-System-Heat-Exchangers-418013-.htm :
ransley wrote:

------------------------------------- Perhaps a little more information would help. The 160 degreewater , from the distribution heat exchanger, will be tempered using 3 Honeywell mixing valves before being sent to circulating pumps then to throttling manifolds for the hydronic tubing. Three mixing valves are used because of the differing types of floors being heated, garage, slab on grade and engineered flooring on joists. The output temperature from the mixing valves will be adjusted to a temperature appropriate for the type floor being heated. The tank water will not be circulated through either the boiler or floor tubing because I'm using cast iron pumps which do not like oxygenated water and will require an inlet pressure of about 5 p.s.i. to prevent cavitation. By using heat exchangers for both the boiler and distribution circuits I'm able to prevent oxygen entering the water and will be able to pressurize each of those circuits to establish the appropriate pressure at the pump inlets. The only thing I've not been able to get a handle on is the required surface area of the distribution heat exchanger. I will check the www.heatinghelp.com site to see if anyone there can advise. Thanks. Magicare

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• posted on January 12, 2010, 2:12 am

not sure this helps but 60,000 BTU/hr = 360 gallons of water per hour with a 20 deg F delta T.
It's probably easier and more accurate to stick some pipe in tank and test for that.
Mark

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• posted on January 11, 2010, 7:55 pm
magicare had written this in response to http://www.thestuccocompany.com/maintenance/Re-Hydronic-System-Heat-Exchangers-418013-.htm :
ransley wrote:

------------------------------------- Perhaps a little more information would help. The 160 degreewater , from the distribution heat exchanger, will be tempered using 3 Honeywell mixing valves before being sent to circulating pumps then to throttling manifolds for the hydronic tubing. Three mixing valves are used because of the differing types of floors being heated, garage, slab on grade and engineered flooring on joists. The output temperature from the mixing valves will be adjusted to a temperature appropriate for the type floor being heated. The tank water will not be circulated through either the boiler or floor tubing because I'm using cast iron pumps which do not like oxygenated water and will require an inlet pressure of about 5 p.s.i. to prevent cavitation. By using heat exchangers for both the boiler and distribution circuits I'm able to prevent oxygen entering the water and will be able to pressurize each of those circuits to establish the appropriate pressure at the pump inlets. The only thing I've not been able to get a handle on is the required surface area of the distribution heat exchanger. I will check the www.heatinghelp.com site to see if anyone there can advise. Thanks. Magicare

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• posted on January 11, 2010, 9:13 pm
On Jan 11, 1:55 pm, michaelsalter_at_gmail_dot snipped-for-privacy@foo.com (magicare) wrote:

The boiler will cook out the oxygen in short order, if it didnt what do you think would have happened to all the 100+ yr old heating systems, this country was built on HW cast iron radiator heat. As far as pumps I think you are mistaken I use a small version of a boiler pump on domestic HW, a recirculator, as do many in large buildings and they dont rust out, and nor do pumps on HW heat, the motors fail or the pumps wear and loose power, Or you could pay and get Bronze but its unessary, its safer than a car radiator waiting to fail.