Hot water base board to heat pump

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  #1  
Old 11-12-15, 04:40 PM
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Cool Hot water base board to heat pump

My house has direct fired hot water baseboard oil heating and indirect oil fired domestic hot water. When oil got too expensive 10 years ago I put in pellet stoves and turned the baseboard heating part of the system off. Even then I was still spending approx. $150 a month on oil just to heat our hot water (we have a 2 person Jacuzzi tub that gets filled every morning by my wife). 2 Years ago I installed a GE Heat Pump hybrid heat pump hot water tank and shut off my oil furnace for good....yay!!! Not only did I save $150 a month on oil, my power bill never changed when I shut the furnace off and turned the new heat pump tank on.

After having said all that my question is this.... we have 2 small bedrooms at either end of the house, on the same floor as the heat pump hot water tank that stay cool during the winter months. So I'm wondering why I can't hook up my heat pump water tank to the existing heating loop(s) through the two small rooms?

I know that the heat pump is 135 degrees as opposed to the furnace that is 180, but the heat pump is ultra efficient..... alternately if necessary I could even change the baseboards in the 2 rooms to low temperature baseboards. Also, if I can do it I'm trying to figure out the schematic, I know I'd need a pump, and maybe a zone valve coming from the heat pump how water out to the heating loop, but I can't figure out the return portion of the loop (just bring it back to the cold water in on the tank?)

Any help would be appreciated!!!

Thanks in advance!
 
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Old 11-13-15, 06:43 AM
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You would need to change the BB to get any effective heat from them at 135 F.
The bigger problem is this, do you want to run domestic water thru them, that will sit stagnate all summer ? Do you know the heat loss of these rooms as you hybrid DHW tank will only produce a small amount of BTU to serve these rooms.
I would expect that it would lower the life span of your hybrid DHW tank, as I have experienced that heating with a gas fired DHW tank will reduce its life by 50% or more, depending on the load on the tank from the heating load.
It will cause you some issues when the heating loads turn on, it will basically deplete your hot water tanks stored capacity, ie you will end up with no hot water when those zones initially start up.
It may not be a legal solution from building code standpoint in your jurisdiction.

So, do I think it's a bad idea... yep.
 
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Old 11-13-15, 04:58 PM
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Won't the existing baseboards heat the bedrooms adequately with the lower temperature incoming water if the radiators run longer hours?

(The FHW temperature must still be substantially higher than the room target temperature.)_

Then all you need is a heat source, any heat source, with enough BTU to heat the water for the baseboards.
 

Last edited by AllanJ; 11-13-15 at 05:14 PM.
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Old 11-13-15, 05:10 PM
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That's what I thought too, and I'm only talking about raising the temperature 5 - 10 degrees celcius. The existing pellet stoves do provide some heat usually keeping the rooms in question at a temp of 10 - 14 degrees celcius...
 
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Old 11-17-15, 05:17 PM
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I am not sure if you understand that as water temp drops the effective output of the heat emitter is reduced.
If the designer sized a 1000 SqFT room to be heated with 100 feet of baseboard at outdoor design temp with 180 F water, it's quite resonable to assume that at 140 these same rads will NOT heat the room at outdoor design temp... no matter how long it runs, or the size of boiler that is attached to it.

since heat loss is a function of the delta tee between desired indoor temp and a given outdoor temp... if the indoor design temp drops or the given outdoor temp is higher your heat loss will be less. The inverse is true, since your pellet stove is doing the easy work of keeping the building between 10 and 14 C, it will take a high water temp to get those BB's to produce the right BTU to bring the up that extra 5 to 10 C.

See lots of failed hobs, and one to remember was a clown that use a 4 ton geo unit to heat a 60,000 btu load which used CI rads for heating. When that failed he added a electric hot water heater to top it up the rest of the way. When the return water is 120 F as it should be when the CI rads are designed for 140F, the geo heat pump is just not adding anything usable, so the entire load was being handled by a 3000W hot water heater. As you can imagine, it did not work well
 
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