# "Hybrid" Hydronic heat system...



## keyman512us (Jul 12, 2007)

Hey all...
Well the title might be somewhat of a 'misnomer' but don't know what else you would call it.

Talking with a 'heating guy' originally from the "middle part of the country" (think like southern NJ or northern MD) I heard of a rather interesting idea.

He told me that in that region (cold in the winter but not all that cold) that some folks had forced hot water (hydronic baseboard) style heat...powered by a conventional hot water heater.

Anyone out there have 'this style of heat'???

What got my curiousity going was the potential application...here in the 'Northeast' for heating in the "spring and fall months" when you need to "take the chill off".

When I bought my house (which has FHW hydronic heat...primarilly off the oil burner) and heating oil was $.68 a gallon...I probably wouldn't have given it a second glance...but roll forward to $2.50+ a gallon and thought "becomes cheap".

Think there might be some potential $$$ savings here to cut back on oil consumption???

Not that far fetched when you consider the majority of "heat pump" systems have electric resistance heaters built in as "backup".


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## Highbeam (Jul 12, 2007)

You still have to heat the water so where are the savings? A dedicated water heater for the FHW system is getting more common here in the NW where they usually use the tankless gas water heaters and recirc the FHW fluid.


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## Eric Johnson (Jul 12, 2007)

I think Webmaster Craig has such a thing hooked up to a gas hot water heater in his office.

It's not all that uncommon, but generally the pros warn against trying to use heating fluid for domestic hot water, unless you've got some kind of heat exchanger. So basically, what you're talking about is using a gas- or oil-fired hot water heater as a cheaper, lower-capacity boiler. Other than the lower cost of equipment, I have no idea if it makes economic sense from a fuel-cost point of view.

If, like me, you have an electric hot water heater being augmented through a coil in a conventional boiler, you might find yourself trying to heat your house with your electric water heater. That's can happen if you turn the hot water heater back on at the end of the heating season and forget to close the valves to the coil. The water heater elements will stay on full-time as the hot water heater convects through the coil and heats up the boiler.

That's one electric bill you won't forget!


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## Reggie Dunlap (Jul 12, 2007)

I have a propane power vented hot water heater that heats a radiant slab in my shop. A circulator pump pushes the hot water through 1000' of PEX tubing and back into the water heater. I leave the water heater at it's lowest setting, around 110-120 degrees.

It's probably not the most efficient set-up, but I got the water heater for free. 

Reggie


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## titan (Jul 12, 2007)

I've seen this done many times in this neck of the woods.....and it doesn't work well.While there does appear to be some good logic for doing it,a domestic hot water heater isn't designed to be a "house heater".........it's recovery time is very slow when compared to a dedicated "boiler"-be it oil,gas,or wood-fired and its' btu output insufficient.The other fault is that folks don't think about the temperature/pressure-relief valve;on a hot water tank it's rated (set) for 125psi while a boiler uses a valve set for 30 psi.That could make a hot-water tank used as a boiler turn into a ticking steam-bomb.


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## Eric Johnson (Jul 13, 2007)

I guess I don't see where a tank full of 160-degree water at 125 psi used for domestic hot water is any less dangerous than the same tank of 160-degree hot water at 125 psi used for hydronic heat. I would just put a conventional 30 psi boiler relief valve on it if it was being used as a dedicated hydronic heating unit, secure in the knowledge that it could handle at least four times that much pressure with no problem. Maybe a pressure tank and domestic water feed, too. Am I missing something? Does the pressure in the domestic water line somehow serve as an auxiliary source of pressure relief?


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## begreen (Jul 13, 2007)

A friend up in Alaska heats his shop this way. He has it connected to an insulated slab with hydronic heat piping. Seems to work just fine.


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## mayhem (Jul 13, 2007)

How about just using an oversized solar hot water system to heat an oil tank-sized resovoir and use small electric pumps to move the hot fluid through your baseboards?  Its proven technology thats been around for decades, just use it on a larger scale to heat your home instead of just 40 gallons of water.

I'm obviously oversimplifying, but does anyone do this already instead of using an oil burner, gas or electric heat?  In conjunction with a wood stove you could reduce your winter heating bills to about $40/month in electricity.


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## cbrodsky (Jul 18, 2007)

mayhem said:
			
		

> How about just using an oversized solar hot water system to heat an oil tank-sized resovoir and use small electric pumps to move the hot fluid through your baseboards?  Its proven technology thats been around for decades, just use it on a larger scale to heat your home instead of just 40 gallons of water.
> 
> I'm obviously oversimplifying, but does anyone do this already instead of using an oil burner, gas or electric heat?  In conjunction with a wood stove you could reduce your winter heating bills to about $40/month in electricity.



I thought about doing this but it's hard enough to supply your domestic hot water, much less have excess for heat in a New York climate.  You'd be looking at a very large number of $1000 solar thermal panels just to make a dent in the heating requirements.

We do use our solar all winter to preheat going into a tankless coil to finish getting to temperature and it definitely helps, but it is not often that you hit 100+ degrees in the solar storage tank during the coldest 3-4 months of the year.  The domestic hot water application is easier because rather than heating 75 degree water returning from the house back up to 100+, you're heating 50-55 degree ice cold groundwater up to 70-90, which is a much easier task.

-Colin


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## Rhone (Jul 18, 2007)

My new energy books recommend doing just that.  Todays houses are built tight and with so much insulation often a hot water tank will have enough btu's to heat a house and provide you with hot water.  Tanks are not rated as efficient as a full boiler but used for dual purpose like heating your house and heating hot water one of the standby losses is cancelled making the hot water tank more efficient than rated.  The most efficient heating system would be one that runs constantly preventing the cycling on/off so, keeping your hot water tank burner running for hours & hours is a good thing (as long as it keeps up).  They recommended a programmable thermostat, so an hour before people start taking showers the heat won't go on giving the tank enough time (if it's been heating during the night) to warm back up fully so others aren't left with cold showers.   You also have the setpoints for the heating system, so you can configure the heating system pumps so they don't turn on if the water in the tank is below 110F which, should prevent the heating system from turning on while people are showering.


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