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[Sconnieman]

First I want to say thanks to all of you here at this site. I've been reading for a couple months now while I have been doing my research on owb's.

I have a 10 plate heat exchanger for my dhw and a 40 gallon hot water tank. I know most here recommend 20 plates, but that's what my dealer sold me before I knew I should get a 20. First question is, should I put the 10 plate first in the series before the water to air exchanger for my forced air furnace, or second after the water to air? I've seen it talked about both ways. Second, should I put the plate exchanger on the cold or hot side of the water heater? I know it's more popular to put it on the cold side, but I've read a couple of threads here where people have them on the hot side and it sounds like it creates an on demand hot water system, which sounds good. My plan is to install a mixing valve either way. I've got little kids, so I don't want 160 degree water at the tap.

[Ridgekid]

First of all WELCOME! 

Since your putting in a mixing valve anyway, I would recommend installing it Before the HWH. Depending on your mixing valve it will add cold only if needed. Then you can kill the power switch to your HWH. How hot the water gets depends on how much you use. We average 145F with no mixing valve. But it is just two of us.

How should you route it on your OWB? Another decision by you. The preferred route is DHWX first. I went HX first, then DHWX. I wanted to get the most of the heat provided by the OWB to keep the house warm. My route will also temper the water a little before it gets to the DHWX.

I not telling you what to do. It's your decision. You will be getting other opinions, you just have to decide what will work best for you.

[RSI]

I would suggest putting it before the furnace heat exchanger and before the water heater.
Also, I would put the plate heat exchangers on unions. Especially if you have hard water. If you have to clean it you don't want to start chopping everything apart.
Dielectric unions work really well and are cheap if you are connecting to copper.

[Bull]

Welcome to the site friend, both good answers.

[Sconnieman]

Thank you for the responses. I do have a question about putting the plate hx before the hwh though. Isn't the hot water only going to enter the tank when hot water is being called for, or does the water somehow always cycle through from the tank through the plate hx even when hw isn't being called for?

Here's how I'm envisioning it. Water heater is turned off, no one has used hot water for hours, tank is full of 40 gallons of warm water, shower is turned on, cold water is pulled through the plate hx and dumped into the hwh tank which mixes with the warm water that's in there which then eventually heats up to a hot temperature. Is that right, or am I way off. I just don't see how the water from the tank would be moving through the plate hx without water being called for, or a pump being installed to constantly circulate water from the tank through the plate hx.

[muffin]

I have my plate exchanger after the tank for this reason.  Seems to work great for me.  Hot water tank is powered off.  I think if you put it before the tank you have to leave it powered on to keep the water hot.  This still should save a lot of moeny as most of the energy is in the heating not the maintaining.  So feel this provides more constant temperatures on the output.  I have not had much trouble with mine.

[Sconnieman]

muffin, I've been talking to dirtryder about his setup and I'm pretty sure that's the way I'm going to go too. I just don't see any advantage to putting the plate hx before the dhwh.

[RSI]

Thank you for the responses. I do have a question about putting the plate hx before the hwh though. Isn't the hot water only going to enter the tank when hot water is being called for, or does the water somehow always cycle through from the tank through the plate hx even when hw isn't being called for?

Here's how I'm envisioning it. Water heater is turned off, no one has used hot water for hours, tank is full of 40 gallons of warm water, shower is turned on, cold water is pulled through the plate hx and dumped into the hwh tank which mixes with the warm water that's in there which then eventually heats up to a hot temperature. Is that right, or am I way off. I just don't see how the water from the tank would be moving through the plate hx without water being called for, or a pump being installed to constantly circulate water from the tank through the plate hx.

The water leaving the heat exchanger will be hotter than what is in the tank. Every time you turn on a faucet you re-heat the tank a little. If you go a long time without running any hot water then the tank will cool and the water won't be hot enough but that usually isn't a problem.
You can add a recirculation pump to keep it hot if that happens.

[Sconnieman]

Here is a drawing of Dirtryder's setup that he sent me. Thought it would be helpful for people that might want to setup their systems this way in the future. Posted with permission from Dirtryder.