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[mtoll]

I read on someones post that DHW draws a huge amount of BTUs, if so is there a way to measure the BTU loss before entering the heat exchanger. If that's a fact why would you not run to the  heat exchanger first.

[RSI]

If you know your flow rate and measure the temperature drop it is easy to calculate btu's.

It isn't a BTU loss, it is just a transfer. You will need to get the same BTU into the water no matter how you do it or what heat source you use.
The DHW is intermittent use so really doesn't affect heating forced air that much. The blower might just run a couple extra minutes. If is having trouble keeping up to heating the house, either the water flow rate is insufficient or the heat exchanger is too small.

If you have the DHW hx after the forced air HX you will get lower temperature to the DHW (when the blower is running) which may or may not be a problem. If you are just using a plate as a pre-heater the higher temperature helps replace lost btu's from the tank between use.

[Uponthehill]

When I finish mine, I am going to my DWH last. We only need ~120 degree DW anyway, so my thinking is why heat it first and rob heat from the house?  Maybe this isn't a common install, but it makes more sense to me. Stay warm...

[mlappin]

Yes and no, unless your running very large lines to your shower and have one of those showers with multiple shower heads, DHW use is relatively low volume compared to the amount of water being pumped thru your OWB lines.

I do have my snow melt system hooked up last, but DHW is first, but it's also a sidearm. You want to pull some serious BTU's off your OWB and make it really work, start up a snowmelt system when it's zero out.

[walkerdogman85]

I would like to have a snow melt system for my driveway some day. How do you control that? Does it run a lot?

[tawilson1152]

My dhw runs off my oil fired boiler and is set up so my heating zones have priority. Is there a reason I don't see owb's set up that way?

[kommandokenny]

I read on someones post that DHW draws a huge amount of BTUs, if so is there a way to measure the BTU loss before entering the heat exchanger. If that's a fact why would you not run to the  heat exchanger first.

My system has a separate loop of 3/4 pex to the DHW .
It's looped off the main 1 inch boiler / FFF loop.
It did not work with a plate exh. on the dhw.
We think it had to do with boiler flow.
Or plate too small,,, [no it wasn't plugged ]

We put in a side arm on the dhw,,,, and xmas.
If your saying that your DHW is stealing from your main loop and loosing potential heat to your house.....?
This works for us.
You can read all about it here]
 
http://outdoorwoodfurnaceinfo.com/forum/index.php?topic=6915.0


kk

[mlappin]

I would like to have a snow melt system for my driveway some day. How do you control that? Does it run a lot?

I have a 7 gallon air tank for a reservoir, came out of that with a piece of one inch pipe, pump connects to that, from out of the pump is a tee, from there one side goes into the "cold" side of a thermostatic mixing valve, the other side of the tee goes to a 30 flat plate heat exchanger, it then comes out of that to the hot side of the mixing valve. Have a strap on temp gauge on the out side of the valve, normally if you start it ahead of a snow you can run 70-80 degrees and stay ahead of the snow. If your surprised by a snow or are getting a lot of wet heavy stuff the temp may have to be turned up to 120 or so. I'm heating roughly 117 feet of sidewalk, takes a lot of wood if the outside temp is getting into the single digits but eventually wood usage tapers off some as the return temp starts to get closer to the temp you're running at.