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[Vincent Paul]

Finally we are ready to start the inside portion of our install.  Our pump will be inside our basement in the mechanical room.  Two questions - first, everything I've read indicates the "hot" water line from the OWB should go to the DHW first then to the furnace.  I want to do the opposite, is there a  reason I can't?  Second question, it is approximately 7' from the wall where the lines come through the wall to either the hot water heater or the furnace, any recommendations on the distance  from where the lines come through the basement wall to where I should put the pump?  Electric hook up is a non issue.  As always, any help is much appreciated.

[AirForcePOL]

I installed my DHW before my furnace because if the house is calling for heat at the same time I'm taking a shower, I don't want my water to get cold.  I could be wrong but I'm going to assume that is the reason for hooking the DHW up first.

As far as the pump goes I'm not sure.  I would think you should put it at the lowest point to prevent any issues with air getting trapped. 

[JTS717]

I ran mine to the DHW (sidearm) first then the furnace.  I just figured most of the time there won't be very much of a loss in the sidearm.  Are you using a plate exchanger for DHW or a sidearm.  A sidearm should pull less heat out of water than the furnace I have about a 15 degree differential across the furnace when it is running so I guess it wouldn't be a big deal if the water in my water heater was only 165.  I guess I can't see why there would be any major issue.  Make sure the pump is low and has head pressure on the suction side and you will be fine.

[CountryBoyJohn]

I think as long a your plate exchanger is plumbed before your water heater tank, you'll be fine hitting your furnace first. I assume it just works out better spacially for you to plumb it this way. Otherwise, yes, it would be better to do the plate before your furnace, based the accurate previous statements. There should be plenty of hot water in the tank to prevent any "shock" from the furnace pulling heat out first.

All that maters with your pump is to try to keep it at a low point in your system. Follow the mooring instructions on your pump and that the motor axis is horizontal.

[Vincent Paul]

We are using a side-arm DHW unit.  I am starting this part of the setup tomorrow after taking an inventory of what is needed and making a trip to Bloomington(IN) Menard's for brass fixtures.  Thank you for your input.  It is much appreciated.  Stay warm, 10 degrees here tonight.  Can't wait to get this unit going, tired of packing firewood to the 2 fireplaces...............vpm

[Maxnchej]

I have a tee off the main line that runs to the furnace and water heater at the same time and seems to be working for me. Instead of a side arm a Used a 20 plate exchanger like a side arm and it is working great. I had had two showers going the sink running hot water and the furnace on without issue. My issue now is my hot water is two hot and need to look at putting in a mixing valve to reduce the temp and this will mean even more hot water to use 

[LittleJohn]

I installed my DHW before my furnace because if the house is calling for heat at the same time I'm taking a shower, I don't want my water to get cold.  I could be wrong but I'm going to assume that is the reason for hooking the DHW up first.

As far as the pump goes I'm not sure.  I would think you should put it at the lowest point to prevent any issues with air getting trapped.

Just think, does your furnace really care if it gets slight cooler water than expected?? Now think, do you care when you get in the shower and the water temperature is slight cooler than you expected 
I always plumb DHW first, cause even with a few faucets/showers running DHW will quickly catch up then send hot water down the pipe to the furnace.

By the way, I have a sidearm plumbed in (with closely spaced tees) immediately following termostatic bypass, and before FPHE for inslab and underfloor application.  I also use a mixing valve on hot side of DHW, as I feel 180f water is a bit warm for my liking when I shower.

[Vincent Paul]

Thank you LittleJohn.  It makes sense to me, I had a friend who recommended hooking up the furnace first.  Since I had no preference one way or the other, I thought I would ask some experts.  Your help is appreciated.

[GCTerpfan]

I have my furnace first followed by my DHW and I have had no issues.  I have a mixing valve installed that reduces the hot water temp to about 140, and my return line is usually never below 150 so I never see a temperature swing in my DHW.

[free heat]

DHW first is recommended, and I have had good luck with my Honeywell mixing valve a must if you have children.

[Maxnchej]

DHW first is recommended, and I have had good luck with my Honeywell mixing valve a must if you have children.

Do you have any picutres how you hooked up the mixing valve, this is something I need to do. My hot water is to hot and I have little kids