What about recirculation pump and pex pipe as a hydronic heater?

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16,404
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Silicon Valley
So if you guys remember I have a loud and oversized furnace for my house and climate (10K BTU for 1500-1700 sqft house in 62F winter) and it is cycling on and off every other 5 minutes, very loud combustion air vent through between 2 bedroom walls, hot and dry air, etc.

So I was thinking about replacing the furnace in the past to something smaller but another idea comes across my head yesterday. What if I install hot water re-circulation pump at the bathroom sink and loop it through a bunch of pex pipe (heat loss = radiator), turn it on at night to blow a small amount of warm air to the room nearby? I do not need it super warm, just enough to keep it warmer than no heat at all is good (need only about 4-5F increase in temperature in about 200 sqft of space). Most importantly I can use very low noise fan at low airflow (i.e. 1400rpm PC fan) and low noise re-circulation pump, or even no airflow and lay a continuous pex pipe under beds.

I don't think the efficiency of the water heater is a problem, it is 60% instead of the 80% of furnace, but I am using just as much as I need instead of being oversize, and it is blowing over a much smaller space instead of warming the whole house.

What do you guys think? Since it is winter only and visible it should be low risk and easy to spot if there is any problem.
 
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9,943
Location
MA
That's why you should do a Manual J calculation to determine how many BTUs you need for the house. I suppose you could use Pex pipes, but why not just get hot water baseboard radiators? Sounds like you don't need much and they come in different sizes starting at 2 feet. Plus you can use those instant hot water heaters as the heater. I do see some units used as both heater and hot water maker.
 
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567
Location
Daytona Beach
Sounds like a THROMBE wall. Are you going to use a storage tank for the hot water?
Anyway, just use some solar pool heat panels for the outside, turned on their side, air vent on top. circulate to the tank if used, the baseboard heaters at night would be better than PEX. You can use the pex to plumb it all together.
If you need more heat, cover the outside in plastic or glass...done.
Probably 200 degree water if in direct sun outside and placed under glass or plastic.
 
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9,943
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MA
This would probably be cheaper and much easier to install.
There are a number of these kinds of products. I just chose this one as a example.

That doesn't sound cheap at all. The slant/fin 2 foot baseboard is about $34.

 

PandaBear

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16,404
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Silicon Valley
Interesting discussion here, now first of all:

1) No boiler, no solar, no storage tank, no permanent installation, no contracting work, no permit. I am not doing any of the permanent work if things don't go well, and have to pay California labor to mess with this.

2) I like the idea of using radiant floor board, that seems like a good idea as it can be DIY, but my loop will likely avoid some of the area instead of evenly apply over the room, and I want one continuous tube instead of connector everywhere. I also am not planning to take out the carpet and redo the floor for this, only to use it to spot heat the room at sleep time by experiment.

3) No manual J or contractor, we are trying to see if we can heat only part of the room that we sleep in, no need to heat where we can't feel it.



Now regarding to water temperature: how do we keep the "loop" at a lower temperature say, 80-100F when the water heater is actually 120F? Do you run 2 pump loops 1 continuous around the room and 1 only on and off to hot water heater in the plumbing? or do you use thermostat like how a car water pump works?
 
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Messages
395
Location
illinois, usa
Do a heat load calculation to find out how much Btu's you need. In some furnaces you can plug or removed a burner or in others the jets can be substituted for a smaller size. You can also get a thermostat that you can control how many times the unite can turn on, mine is set to 3 per hour and get very nice long heating runs.
 
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9,943
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MA
There's also several free heat loss calculators out there. Here's one from Slant/Fin.


As for the water heater, isn't there a thermostat on it that you can turn down?
 

PandaBear

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16,404
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Silicon Valley
There's also several free heat loss calculators out there. Here's one from Slant/Fin.


As for the water heater, isn't there a thermostat on it that you can turn down?

I was using a chart that turns out to be 20 BTU/h/ft, on a 100 sqft room it is 2000 BTU, plus another room together would likely be about 4-5000 BTU. Yes there is a thermostat on water heater but you need to keep it at around 120F to avoid something growing and hot enough for shower.

 
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...
A 1500 watt 110 electric heater with a thermostat would be SO much simpler for spot heating.

But coming up with your own solution is much more fun!

Or a electric blanket, unless California has outlawed those.

This idea seems like a lot of thought and expense just to heat one small area. It is a interesting discussion though. My thought is that floor heating is very nice but where you live puts the return on investment into question.
 
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9,943
Location
MA
I was using a chart that turns out to be 20 BTU/h/ft, on a 100 sqft room it is 2000 BTU, plus another room together would likely be about 4-5000 BTU. Yes there is a thermostat on water heater but you need to keep it at around 120F to avoid something growing and hot enough for shower.
If it doesn't get that cold that often, the easiest thing to do is to just put in some electric baseboard heat. This little 3 foot electric baseboard heater is 2560 btus.


Don't use those portable electric heaters, they're considered a fire hazard, even though they're mostly safe these days. Basically because you can draw a lot more current from the wires which can cause an electric fire. If you have dedicated heaters, they have their own separate wiring so you're not as likely to draw too much current.
 

PandaBear

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16,404
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Silicon Valley
We have electric blanket, it was fine for my children but my wife seems to have a problem with the "air" of the room feeling kind of cold when only using blanket and too hot and dry when the furnace is on. I won't use standing portable electric heater as you said it is a big fire hazard. So in a way I was thinking a few loops of PEX with circulation pump during winter time would be a good work around. Mainly my goal is just enough heat flow without too much noise and capital investment, not really floor heating but just laying them along side the wall (so you won't step on it) and under the bed, spreading the heat gradually to keep the room "not cold" would be sufficient.

750w 240v means if I use 120 it would be 375w, probably around 3-4 KWh a night, not too bad of an investment and without plumbing to deal with.
 
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9,943
Location
MA
We have electric blanket, it was fine for my children but my wife seems to have a problem with the "air" of the room feeling kind of cold when only using blanket and too hot and dry when the furnace is on. I won't use standing portable electric heater as you said it is a big fire hazard. So in a way I was thinking a few loops of PEX with circulation pump during winter time would be a good work around. Mainly my goal is just enough heat flow without too much noise and capital investment, not really floor heating but just laying them along side the wall (so you won't step on it) and under the bed, spreading the heat gradually to keep the room "not cold" would be sufficient.

750w 240v means if I use 120 it would be 375w, probably around 3-4 KWh a night, not too bad of an investment and without plumbing to deal with.

Your math is a little weird. That would be 3-4kwh max. That's based on the coldest night in your area. Other nights probably not even that much, you basically just set the thermostat.
 

PandaBear

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16,404
Location
Silicon Valley
A slight twist to the same idea (my wife shot down recirculating from bathroom faucets):

Our water heater, furnace / air handler, duct work all go through the garage on the same side of the wall. The water heater actually sit right on top of part of the duct before entering the furnace, so you probably know what I am thinking already. I want to T the inlet and outlet of the water heater into a big loop of pex inside the duct, with the recirculating pump, and use a thermostat to control the pump on off, while setting the pump to the lowest flow I can. In theory, there would be minimal work other than drilling 2 holes into the duct and loop about 80 feet of pex inside, two tee to the water heater, a pump, and a thermostat. If there is a leak it would be like a water heater slow leak, into the garage the duct pass through the garage floor onto visible part of the garage. This would let me downsize the furnace from 100K*80% BTU to probably 60K*60% BTU max, but reducing the flow of the pump can probably make it closer to 5-10K, this would be enough to keep the air flow all day and just enough heat for 68-72F all day continuously, while still using natural gas instead of electricity (5x cost). Material cost would still be about $100 for pump, $40 for pex, $40 for tee and $40 for valves. If I can wire out the existing thermostat I do not need a new thermostat.
 
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Pacific Northwest

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19
Location
Phoenix AZ
If you go this route, use a TACO circulation pump, and control it using a smart plug. These pumps are used in in-floor water based heating systems and draw just a few amps.

These pumps are very reliable. And, if you do wear it out, it is a cartridge style pump. The mechanical portion of the pump is in a cartridge, and easily replaced by removing 4 screws. Just isolate the pump with inlet and outlet valves when you install it.

TACO
 
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