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Author Topic: Forced air furnace for in floor heat?  (Read 557 times)

RSI

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Forced air furnace for in floor heat?
« on: September 07, 2017, 05:13:06 PM »

I have a customer that has in floor heat in the basement that will only be connected to the outdoor boiler. He want the forced air LP furnace to use the heat exchanger backwards.

It is a brand new really well insulated house so I don't think circulating water through the plenum when the blower is off will work. Also, if it is pulling water through the main loop, that would mean the LP would have to keep the OWB warm enough to heat the floor.

I have thought of a couple ways that it can be done that should work but doesn't seem like it is worth the trouble and expense.
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mlappin

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Re: Forced air furnace for in floor heat?
« Reply #1 on: September 07, 2017, 05:55:58 PM »

Iím not comprehending this, so the wood boiler is only going to heat the basement floor and the LP furnace will be doing what exactly?
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Re: Forced air furnace for in floor heat?
« Reply #2 on: September 07, 2017, 06:29:31 PM »

Rest of house has forced air heat. There will be a heat exchanger in the plenum.
The floor heat will only be heated from the OWB.

What he wants is to be able to heat the floor when the OWB isn't running by backfeeding heat from the LP furnace into the water.
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mlappin

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Re: Forced air furnace for in floor heat?
« Reply #3 on: September 07, 2017, 06:46:53 PM »

Okay, gotcha.

Just about need to set up a mini loop of some kind so the LP furnace is heating a minimum amount of water.

Like you already said, not sure its worth the hassle and expense.

Shoot em a quote for a standard install then list what he wants as an option.
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Re: Forced air furnace for in floor heat?
« Reply #4 on: September 10, 2017, 12:01:58 AM »

I think it would be too hard to make it have any consistency since it would only be heating when the forced air furnace was calling for heat.
I am going to skip it for now and it is needed will use a plate hx on the water heater and a couple pumps.

Another issue I am trying to decide how to hookup is the radiant loops. There are 5 in the basement floor, one in the garage floor and two for snow melt in the sidewalk.
He wants the garage floor to run together with the basement floor which seems like will not work that well.

I am thinking about just going with an 8 loop manifold and putting actuators on all the loops. Then using an ECM pump and letting it deadhead when there is no call for heat. I would probably tie the 5 basement actuators to a single thermostat.

 Is there any problem using the same temp glycol in the snow melt loop as in the basement floor? If the temp has to be different, I would probably use a standard pump for the basement floor that is controlled by the thermostat (no actuators) and do a 3 loop manifold with actuators for the garage and snow melt.
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Re: Forced air furnace for in floor heat?
« Reply #5 on: September 10, 2017, 04:52:13 AM »

Why not simply use 3 seperate secondary loops off the primary wood boiler plate exchanger loop, each using its own properly sized circ, one for the basement, one for the garage and one for the snow melt, the snow melt could be controlled by manually turning it on or by a 60 minute timer or manual bypass and basement / garage each on their own TT. Be sure that the radiant side of the plate exchanger has proper expansion control and pressure relief and it will be fine with all the same anti freeze.
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Re: Forced air furnace for in floor heat?
« Reply #6 on: September 22, 2017, 11:41:52 AM »

Seems a bit unwise to use the same manifold set for snow melt as for in floor loops.  The delta on that would be all whacked.  You would want no mixdown for the snow melt, but you would for the in floor loops, so if you used the same manifold the snow melt would be very inefficient, with the low initial temp.
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Re: Forced air furnace for in floor heat?
« Reply #7 on: October 15, 2017, 01:46:44 PM »

I may be a little late to the party here, but I hope you're planning on piping a plate exchanger into the boiler loop and running the radiant off a pressurized loop. I prefer individual pumps for each zone over a single loop pump and zone valves, but that's just me. 8 zone valves when 5 are on the same zone AND deadheading the pump? Come on man. Run a 1" copper loop through the plate, mixed down to 100ish degrees with 3 tees on both a supply and return header. Each zone would have it's own pump, garage and basement stats would power those 2 zone pumps and the snowmelt on a 12 hour timer or switch or whatever the customer wants to power the third pump. Each zone can run independently or all together with no risk of fighting each other. How small is this garage that it's only 1 loop??
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Re: Forced air furnace for in floor heat?
« Reply #8 on: October 15, 2017, 10:10:04 PM »

The way wreckit87 lays it out is just about the same way my contractor laid out my 3 in-floor radiant systems. When I'm not using my OWB my Geothermal heats a buffer tank (modified 40 gal water heater tank) which feeds my 3 zones each having it's own T-stat controlled pump which is properly sized for each zone. When my OWB is running, my second take off from the indoor primary loop is a 40 plate heat exchanger to heat the buffer tank (faster than the Geo does). Slim Jim recommended using mono-flow tees in my primary loop to feed each of my 3 loads and it has worked out fantastic.   
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RSI

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Re: Forced air furnace for in floor heat?
« Reply #9 on: October 16, 2017, 07:31:25 AM »

I may be a little late to the party here, but I hope you're planning on piping a plate exchanger into the boiler loop and running the radiant off a pressurized loop. I prefer individual pumps for each zone over a single loop pump and zone valves, but that's just me. 8 zone valves when 5 are on the same zone AND deadheading the pump? Come on man. Run a 1" copper loop through the plate, mixed down to 100ish degrees with 3 tees on both a supply and return header. Each zone would have it's own pump, garage and basement stats would power those 2 zone pumps and the snowmelt on a 12 hour timer or switch or whatever the customer wants to power the third pump. Each zone can run independently or all together with no risk of fighting each other. How small is this garage that it's only 1 loop??

This project is currently on hold.
Zone valves are not exactly the same as manifold actuators. It doesn't hurt an ECM pump to deadhead it. They are designed to work that way. It wouldn't be a big deal to shut it off either though. Also, the ECM pump will keep a constant head pressure so not sure what you say would be fighting each other.

I didn't have anything to do with the pipe install so if that is done right or not doesn't matter. It needs to work as good as possible the way it is.
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wreckit87

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Re: Forced air furnace for in floor heat?
« Reply #10 on: October 16, 2017, 11:51:18 AM »

I may be a little late to the party here, but I hope you're planning on piping a plate exchanger into the boiler loop and running the radiant off a pressurized loop. I prefer individual pumps for each zone over a single loop pump and zone valves, but that's just me. 8 zone valves when 5 are on the same zone AND deadheading the pump? Come on man. Run a 1" copper loop through the plate, mixed down to 100ish degrees with 3 tees on both a supply and return header. Each zone would have it's own pump, garage and basement stats would power those 2 zone pumps and the snowmelt on a 12 hour timer or switch or whatever the customer wants to power the third pump. Each zone can run independently or all together with no risk of fighting each other. How small is this garage that it's only 1 loop??

This project is currently on hold.
Zone valves are not exactly the same as manifold actuators. It doesn't hurt an ECM pump to deadhead it. They are designed to work that way. It wouldn't be a big deal to shut it off either though. Also, the ECM pump will keep a constant head pressure so not sure what you say would be fighting each other.

I didn't have anything to do with the pipe install so if that is done right or not doesn't matter. It needs to work as good as possible the way it is.

By fighting each other, I meant fighting for flow and/or temp. Lets say the way you proposed, if the snowmelt was running and sending 0 degree glycol back into the loop while the garage was calling, what temp fluid is the garage going to get? I'm aware of the difference betwixt actuators and zone valves, that was my politically incorrect side speaking- but the fact remains that 3 pumps would be considerably more effective and 1/3 the work of actuators and an ECM. The reason I mentioned the piping is because you proposed building manifolds and the whole deal anyway, so "the way it is" obviously is nothing. I'm not standing there, I can't see it, but the way I have it pictured in my head is a complete dumpster fire. If it works, great, but I prefer doing things correctly over throwing a bunch of crap together and hoping it does things. Merely trying to offer some constructive criticism that I know works as I've done it dozens of times and have 40,000 hours of hydronics under my belt, but I apologize if I got my wires crossed. Good luck!
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RSI

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Re: Forced air furnace for in floor heat?
« Reply #11 on: October 16, 2017, 05:11:18 PM »

I wasn't trying to argue, just make sure we are talking about the same thing. I am still not sure we are.

I am not planning on building manifolds. I am going to use radiant manifolds with flow gauges and balancing valves. The actuators just go on the existing valves.

Won't the cold return glycol go straight back to the heat exchanger? One pump or 3 will all draw from the same place and return to the same place.

I still don't see the point of using 3 pumps. Since head pressure doesn't increase with more loops, the flow won't be that much less with a single pump than with 3 pumps.


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wreckit87

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Re: Forced air furnace for in floor heat?
« Reply #12 on: October 18, 2017, 09:19:47 AM »

Sorry, I had something completely different in my noggin for some reason. You are correct, it would go straight back to the HX. I still stand by using 3 pumps with individual manifolds to keep the loops separated, mostly due to the fact that if the sole pump decides to take a crap, nobody gets any water... I just like to ensure that everything is separated and self sufficient, plus I don't like the idea of the actuators. Cost would be in the same ballpark either way, with a lot less wiring and clutter IMO. My $.02 aren't really important though, if you're content with it by all means do it up!
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