Posted By ilgeo on 19 Aug 2010 02:43 PM
Some thoughts..
5" will take awhile to warm up but I understand why u want to do it. I would recommend that you set the space with floor heat around 5* warmer than the rest of the house when unoccupied as that will cause it to run as it takes on part of the load for rest of house. During construction I have seen 65* basement keep a tight ranch at 58 to 60* also the rest of the house will warm up quickly on FA and you also store more heat in the event of a power outage. So maybe try 50 up and 55 to58 down and see how it goes. Then start with load calc and design from there. You will need a heat exchanger, 1 bronze pump, 1 CI pump, expansion tank, PRV and dual check, strainers, air eliminator, pump relay, manifold , and zone valves. What do you mean your electric water can bring the water temp to 125*? Are the elements hooked up? They should not be wired to line voltage.

The electric hot water heater is after the navien the electric was there already and newer so I decided to keep it as an option in case I run out of propane sometimes when rented will turn on only the electric to prevent over usage of hot water.  There are three showers one with two heads minus all restrictors and 2 laundries in the summer its not uncommon to have several things running.  There are several ball valves that allow me to bypass navien completely with the domestic or bypass the electric completely power outages and so forth the system may be complicated but I like options.  I have tees on in and out supply on the navien ready for the heat exchanger loop.  Probably should have done a load calc but didnt know how i figured the 175000 max btu was probably overkill and also had the fan forced heaters for supplementary heat and also to take the basement up to temp initially. On the midfloor I have a propane wall heater 80000 btu two 2000 watt wall heaters a woodstove and firplace top floor just baseboards in the bedrooms.  It seems to heat up quickly in the winter.  The radiant downstairs is to add comfort since it is a colored concrete floor it is pretty cold even when the air is warmed initially.  I have two runs at 265 in the main room zone One run of 100 for bathroom zone One run of 300 for the sunroom.  The sunroom is all windows with water proof deck above and french doors from the basement this room has only radiant to heat but may not be on all of the time I imagine there would be alot of heat loss in the sunroom.  The bronze pump that was recomended in the heat exchanger loop will it be turned on by the controls when radiant call for heat and will it shut off and give priority to the domestic if the controller has priority built in?  How many gallons per min should the bronze pump push through the loop? Does an alpha seem like a good fit for the zone circulator pump I know its more money but I saved alot doing all this myself so far.  One more question I have heard of a thermostat that can be adjusted over the phone lines good for vacation homes is this true? Probably expensive though.  This website has been a great help and so have all of the professionals your advice is greatly appreciated Thanks Oh zip is 98370 Ive never seen basement go below 53 degrees on the coldest days of winter with no heat on.  

Should I go with a 20  plate or 30 plate heat exchanger?

Posted By BadgerBoilerMN on 23 Aug 2010 04:01 PM
If you have a set of plans, a heat load can be done. If you know available fuels and their cost, a heat source can be specified. If you have the heat load AND the heat source, then a plate heat exchanger can be sized using factory design software.

I design radiant floor systems and find competent installers all over North America, but rarely find a good excuse for using a tank-less water heater for space heating.

Of course, I do sell them for their intended purpose, but without outdoor reset and with 25%+ more fuel usage, the cheap solution is rarely the right solution.