tankless heater to temper boiler
Hello to all. Please save the wit and sarcasm for another post. I have an oil fired hydronic heating system using heat pumps as the primary heat source. I enjoy a whole house electric heat rate discount of aprox. 50% during the heating season, from Oct- March. I would like to take advantage of the low electric rates, and temper the return water with a tankless electric heater, such as the Stiebel Eltron. My boilers are rated at 250kbtu. My simple logic tells me that for every degree of heat applied to the return water before it enters the boilers, the less the boilers need to work, thereby lowering (I hope significantly) my oil bill. I would like to use the smallest tankless unit, not expecting it to handle all or even a portion of my hydronic needs, but simply to raise the return water temp. a few degrees, or more if it is cost effective. Your thoughts and professional opinions please.
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Heating water electrically is very energy inefficient and depending on your electrical rates, probably not cost effective. Water heated the way you're doing it now is probably fairly efficient, for your intended use, but if you would like to explore use of solar heating water, then you might have something. The problem there is that when the outside temperature drops, the chance of freezing the solar panels represents a very real problem. Most will drain them in winter.
If your burning oil, where does the use to heat pumps come into play. I thought heat pumps were electrical, reverse of refrigeration for heat and refrig for cooling etc! What am I missing here?
woodway- thanks for your response. my heating system is multi zone heat pumps, with hot water coils in the air handlers as a back up. the herat pumps provide air conditioning, as well as heating during moderate climate conditions.Baseboard been VERRRY good to me
It may make sense, financially. Or you could use a tank type heater -- would be a toss-up in terms of operating cost so it's a tradeoff of space vs up-front cost and current limitations.
Please be careful to know that electrically heating your water is less expensive than with oil. In most areas of the country, I understand that oil and electricity have similar costs.
Be very careful which tankless heater you buy. Certain electric tankless models do not like warm water at their inlet. I know that Seisco can take warm water input since it does not work on flow but rather on temperature. The Seisco will do exactly what you want to do but the real question, is it a good investment.
Bill
Thanks BillHoover. The only reason this is a viable project is the 50% discount that I get on electricity during the heating season because of my heat pumps. I had not considered the warm inlet factor and will do more research. Perhaps a tank type unit is a lower cost alternative.Baseboard been VERRRY good to me
If electric heat is cheaper than oil then the scheme might make sense if you can recoup the cost of the auxiliary heaters in a reasonable time. So what is a reasonable time? Depends on your rates and the continued existence of that 50% discount from the utility. Most of the incentive programs I've seen have fine print that says they can discontinue the program whenever they feel like it.
Technically, can the heaters handle the flow rates in the return lines and are they rated for continuous operation at the exit temperature you want to achieve?
also, lowering the apparent load on the boiler system will increase cycling frequency and may reduce boiler efficiency and lifespan.more than the energy offset/savings? very, very hard to say.
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Interesting idea but why not do something that costs nothing to run?
I would work on adding insulation and reducing the heat load first.