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make me all warm inside
October 15, 2008 9:06 PM   Subscribe

What is the difference in efficiency between plain old ordinary electric heaters and hydronic electric heaters?

I need to replace the electric heaters in a weekend house. Getting new standard electric heaters will cost around $3500 and getting hydronic baseboard heaters will cost around $7500. The people selling the system say that the hydronic heaters will be more efficient since the oil they are filled with stays warm longer than the aluminum radiators of the standard electric baseboards.

Well.

I was born at night but not last night and that does not make sense to me: if it takes longer to cool down it will take proportionally longer to heat up. Yeah maybe, says the plumbing guy but alls I know is that the hydronic ones are more efficient so you will make up for your pricier heaters with by using less electricity to heat the house.

We finally wind around to the question: are the electric hydronic heaters more efficient than standard electric baseboard heaters, by roughly how much and, ideally, why?
posted by shothotbot to Home & Garden (8 answers total) 1 user marked this as a favorite
 
Here's some related information.

They note that "Hydronic (liquid-based) systems use little electricity" but they might be referring to systems that use water heated by gas.

Also, this may apply: "Time-of-use rates allow you to "charge" the concrete floor with heat during off-peak hours (approximately 9 p.m. to 6 a.m.). If the floor's thermal mass is large enough, the heat stored in it will keep the house comfortable for eight to ten hours, without any further electrical input."
posted by alexei at 9:24 PM on October 15, 2008


That's a good website that alexei posted.

I would like to add the point that putting liquid piping under a floor has the risk of a potential leak. I would be concerned about the lifetime and reliability of the system.
posted by abdulf at 9:31 PM on October 15, 2008


We are not talking about the type which pumps hot water around. The electric baseboard units are self-contained and swapable for standard electric ones. The only difference is what you are heating (with your electrons) metal or fluid.
posted by shothotbot at 9:36 PM on October 15, 2008


How could they be "more efficient?" An electric heating element turns 100% of the power it consumes into heat, unless, I guess, it gets so hot that it throws off some visible light too, but we aren't talking about that.

I vote for plumbing guy being wrong.
posted by Good Brain at 11:36 PM on October 15, 2008


Sounds like it's a variant on a storage heater: doesn't use less power, but does allow you to use cheap night-time power. Having suffered in a couple of UK apartments with storage heaters, it's never as controllable as you'd like.

Electric heating is the least efficient form of space heating there is, but you may not have a choice in your structure.
posted by scruss at 4:27 AM on October 16, 2008


I look at manufacturer-issued data sheets for hydronic heaters and I don't see any mention of higher efficiency. Which makes sense because, as Good Brain says, you would expect any electric heater, hydronic or not, to be essentially 100% efficient.

Alexei is right too: In some places electricity is cheaper late at night than it is at times of peak demand - hence storage heaters exist that produce heat when electricity is cheap and use the heat to heat the room when required. Of course, you only save money if there are different power prices on offer, and these baseboard heaters aren't quite the same as storage heaters.

On balance I too vote for plumbing guy being wrong - I don't think the hydronic electric baseboard heaters will be any more efficient.
posted by Mike1024 at 4:48 AM on October 16, 2008


Heat loss in your house is determined by two major things.. the inside/outside temperature differential and the thermal resistance of the interior to the exterior.

Every BTU of heat you lose due to this heat flow at your desired setpoint temperature has to be replaced or your house will cool off.

Variations on the theme of how resistance electric heat provides that energy are essentially zero. A 1 KW element uses the same amout of power if it is heating air as if it is heating oil. Leave it on for an hour and it's a kiloWatt-hour of power.

There is no difference in efficiency, only differences in the heat response of the thermal transfer medium.

There are OTHER performance differences, for instance, including the ability to time-shift energy consumption, which might enter into the analysis if you live in an area with peak load pricing and/or time of day pricing.

(This question is a variation of the 'is my refrigerator more efficient loaded than unloaded' that comes up here from time to time. Same answer. It does not affect the efficiency of the local system. To be extraordinarily picky, it may have infinitesimal effects on the larger system including the power company generators and grid due to the amount of idle capacity they keep online to deal with microsurges in demand, but in the local system consisting of your house and its internal air, no difference at all.)

Your plumber is dead wrong. There may be many reasons to use his system, but efficiency is not one of them.

Contrast a heat pump and a resistance heater and you can talk efficiency differences, because of where the heat comes from, but resistance is resistance.
posted by FauxScot at 5:01 AM on October 16, 2008


I think that the hydronic baseboard heaters are just a marketing gimmick. A true hydronic system has an array of heat carrying water pipes embedded in a floor and covered with a thin layer of concrete. This is a very comfortable heating method for two reasons: the heat rises from the entire floor so that the floor is never a cold spot and because the concrete has thermal mass that evens out temperature changes.

I believe the hydronic baseboards are just trading on the name recognition of the in-floor hydronic system without providing their unique features.

In terms of efficiency, if by efficiency you mean cost of operation, then either a standard electric or hydronic baseboard heater will be the same. A kilowatt-hour of heat is the same in both cases.

In terms of control theory, the baseboard hydronic system will perform worse for comfort because it has a slower response time to temperature changes in the room. When the room gets colder, the hydronic baseboard heater takes a while to warm up, allowing room temperture to drop lower. When the room gets warm, the hydronic heater continues to put out heat even after it shuts off, causing the temperature to overshoot. This is because the baseboard hydronic heater does not have the concrete thermal mass of the in-floor systems to smooth out the changes. In a control system to maintain a steady state you can have either a very fast response time to counteract changes (like the standard electric baseboard heater) or else you can have a damping system (like the thermal mass of concrete in-floor hydronic systems). With the hydronic baseboard heater you have neither.

There may be one possible advantage of the hydronic baseboard heaters. Because of the slower heating and cooling of the heating element due to the fluid in the copper pipe, there may be less popping noises as the sheet metal expands and contracts.

So unless someone can demonstrate that the hydronic heaters indeed do eliminate annoying pops compared to standard baseboard heaters, I would be inclined to save the money and go with the cheaper heaters.
posted by JackFlash at 1:54 PM on October 16, 2008


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