More efficient water to air HX set up

[hondaracer2oo4]

I have a Hardy H4 outdoor boiler, we all know that it is not the most efficient design but I have a buddy who has a Shaver and that thing isn't very efficient either! Well he has a water to water exchanger and I have a water to air exchanger. This time of year he can go for 36 hours easily between loadings(doesn't load it up very much either). I can usually not do more than about 24 hours if I fill my Hardy up. My thought is that he isn't losing the heat in the heat exchanger like I am, we both run the pumps 24/7. My Hardy is also been spray foamed so I know that I am losing less heat at the boiler itself most likely than he is with just regular insulation. So my question is what are my options to keep from losing alot of heat at the HX? I have thought about only running the pump when calling for heat(worried about possibly pipe freezing in the winter, dont know if that is a legitimate worry though) also thought about a bypass valve inside that diverts the water around the hx when the thermostat isn't calling for heat. What is your experience with losing heat at the water to air hx? Also what are your ideas?

 

[wrightk20]

I have a air to water heat exchanger in my house and i pump 24/7. In my house i can feel water air at the forced air vents all the time with the fan not running so i'm assuming in your case that your always losing heat because of the heat naturally rising. If your lines are buried far enough and insulated i wouldn't think the lines would freeze. You could try and switch your pump on when your house calls for heat although with a fire going all the time in the stove i don't know if one would have to worry about hot spots in the stove. i know with my setup that my fan doesn't run near as much as if i would just let the furnace heat the house because it is always adding heat in a little bit all the time. Obviously you guys aren't heating the same house so you would have different heat loads from each other. Switching the pump might work but then you would cycle your pump and your fan would run more and longer i would think. Kevin

 

[Encore]

I have the same setup you do and I can go around 36hrs between loading times when the temp is around 45-60 degrees during the day.

My pump only runs when heat is called for and I think that's probably where you're losing a lot of heat.

Most of the guys I know don't run their pumps 24/7 unless its really really cold. But even then it's just a precaution. If your water temp is high enough I would imagine it'd be pretty extreme for it to freeze.

 

[wrightk20]

I guess the way i'm thinking is if you run the pump continuous your really only loosing the heat through your lines because the exchanger in the house would pull heat off but it wouldn't technically be wasted because the heat is going into your house. i have thought about having my pump only run with demand but with my sidearm water heater and on these mild days my water would probably cool off to much. Kevin

 

[12vdzl]

Are either of you heating your DHW? Could there be differences here?

I don't recall seeing what type of insulated pipe both of you are using. Again, could this be the difference?

I have a hawken, I can go 36-48 hours on just 6 pieces of smallish, warm weather wood (pine, etc.) I also have an air to air exchanger, no DHW tap, and am using 110' of thermopex buried 2 feet.

 

[applefarmer]

Yep my hawken can also easily go 36 hours with these type of temps. My pump runs 24/7 and I also have thermopex for underground pipe. Not knowing anything else I would guess differences between underground pipe, heat load, and size of firebox would make a lot more difference between fill times than a pump running 24/7. I personaly would never have a pump that cycles, as the heat that radiates off the exchanger from constant water movement is keeping everything much more consistant in the house, and as long as it is going into the house I don't consider it being wasted.

The exception would be if your losing heat to the ground, through your pipes. In that case a on demand pump could save you some wood, and just because your pipes are buried deep doesn't mean they are not losing heat.

 

[Butch(OH)]

You are barking up the wrong tree in blaming the exchanger. For all practical purposes there is nothing to lose in the exchanger itself. With the fan off the water is more or less just circulating, when the fan is running it takes BTUs from the water and puts them in the ductwork, the exchanger can't make BTUs or lose them, it simply transferrs then from one form to another. Either your demands are higher than your neighbor or your stove is less efficient or your losing heat in the ground.