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[Propster]

Hi all, I'm new to this forum. Let's just say I wish I had found you all awhile ago. I have a '96 Aqua-therm model 145 (the smaller one). Came with the place when I bought it a few years later. I have several issues that I have basically been overcoming over the years, and have learned anything I know on my own. But I'll address them all separately, assuming I can/am able. Please bear with me while I explain.

So the older gentleman that added this unit to his existing propane forced air furnace seemed to have taken a bit of an unconventional route. Instead of running water pipe underground into the house and thru a heat exchanger inside, he built a shed to house the boiler not far from the house. He then did just a short run of water pipe inside the shed and thru a heat exchanger out there, then buried a 10 or 12" PVC pipe underground and into the basement furnace room and into the plenum of the propane furnace. So basically it's a forced air system with a very short run of pipe.

When the room thermostat calls for heat it kicks on the motor that drives the heat exchanger. The problem is that the heat exch runs for quite a while but the furnace fan only kicks on a few times during that time and blows warm air into the house for maybe ten seconds per time. So it's drawing heat off the water pipe continuously but not putting all that heat into the house. We'll address that a bit down the road.

My immediate question is what is generally recommended for the aqua stat setting between 160-180 that will allow the stove to keep up the heat without going thru the wood as fast? Am I better lower, say 170, where the stove can rebuild the heat quicker but I assume the air blown into the house is less warm, or 180 where it may take longer to get it back up to temp?

I'll follow up on the other questions, unless the answer to this one is related to fixing those first. I appreciate anyone who has stayed with me this far and is willing to offer some advice. Thanks!

[Wood Nutt]

Aquastat temps are discussed on here all of the time and opinions and time of year settings will vary but you are probably going to be closer to the 180 mark.

So if I understand correctly, you basically have a unit heater in the small shed where your OWB is and it has a forced air fan motor blowing across a water to air HX and into the 10-12" pvc which is acting as an air duct, correct?  Then your furnace fan inside the house is then only an air booster fan if I understand correctly?  Is there only one of these large PVC pipes or two and is/are they insulated?  For that kind of system to have a chance at working, it would need 2 big pipes, a warm air from the HX into your house plenum for heated air and a return on the upstream side of the outside HX for the cooler supply air into the outside HX.

If there is only one big pvc pipe, can you use it as a conduit and pull a boiler water pipe set into the house and move the HX into your house furnace plenum?

[slimjim]

Good answer wood nut, hot air loses it's energy very fast where hot water can be used to transfer it's heat over great distances in much smaller lines, put the air handler in the house and run hot water to it, yes you will burn more wood with higher temps on the Heatmor

[Propster]

Sorry for not being a little more clear and complete with my explanation. I will stick with the 180 by the way, that's how I was leaning. The boiler is outside in the shed. There is no fan outside in the shed, only in the propane furnace in the house.  There are two large pipes, one for the warm air blowing into the house (into the plenum), the other is a cold air return from the house that feeds the HX out in the shed.

I realize this is not the most efficient system (forced air outside vs bring a longer run of water pipe into the house and then drawing the heat off via a HX), but until I can afford to run the pipes inside and add a HX or radiators it will have to do.  However, it works surprisingly well especially if we can get into the teens or higher for temps. It's when the highs during the day are 0 or below and it gets down well below zero at night that is a problem.

So here's my next challenge: fixing it so the HX doesn't run so often without the furnace fan blowing hot air into the rest of the house. Said another way, whenever the room calls for heat and the HX kicks on, that the fan kicks in very shortly after and continues to heat the house so that it gets to temp faster and the fan kicks off, so does the HX. This should allow the wood to last longer by not losing as much heat from the water pipe.

One guy suggested I add a relay to sync the furnace fan with the HX so they're on at the same time. But he said I'd also have to run the 'warm air in' pipe thru the cold air return of the propane furnace instead of the plenum. This may be beyond me, plus that 10-12" PVC pipe I don't see how I could reroute that thru the return of the furnace.

So I'm wondering if something else is causing the problem. Are there limit switches or something in the furnace that may not be working, and that what is preventing the furnace fan from staying on longer?
Thanks guys!

[slimjim]

I'm still not sure I understand your dilemma, try to understand that your installation is not typical at all! You have a fan rad combo outside in the shed blowing hot air through ductwork to the plenum of your hot air furnace, am I right so far.

[ITO]

 If I'm understanding your setup, there may be a high heat sensing switch in the plenum that shuts down the furnace fan, if you follow the wiring from the fan the sensor (if there is one) will be in series with it, many times they are just a flat disc screwed onto the duct. The problem with bypassing that sensor is when you are using the propane furnace you need that sensor wired in.

[RSI]

Is the propane furnace older? If it is, is there a  silver box on the plenum about 4" wide and 6" high with a wire going to it?

If you have it, pop the cover off and lower the set temperature as low as you can without it running continuous.

I would get the heat exchanger moved to the plenum as soon as possible. It shouldn't cost very much.

[Propster]

Slim,
You are correct except there is no fan outside in the shed, just the HX.
RSI,
I'll look for the silver box you describe. Are there any controls or anything on the outside of that box? Is the temp setting you're suggesting I adjust, the high heat sensor that ITO refers to?
And as far as getting the HX moved to the plenum, that will only work if I also extend the water pipe inside as well correct? Otherwise how would moving it in to the plenum allow it to draw any heat off the pipe if the pipe remains outside?