Adding Electric Reheat to Existing Duct

[gdocktor3]

I just had solar panels installed and I’d like to utilize the electric power to heat my house. Because I plan on doing an addition in the near future, I don’t want to spend the time/money on a heat pump without knowing the exact size I will need. I haven’t decided on how big of an addition yet, but our two bedroom house is getting tight with two dogs, a new baby and a wife who wants another. I currently have a Spirit (Thermopride) oil fired 3 ton unit and they don’t offer electric heat or heat pump for my ahu. I know strip heaters are installed to supplement heat pumps in real cold areas. I’ve also seen electric duct heaters like THIS that seem pretty straight forward and easy to install, just curious if anyone has done it before? I’m also wondering if I should/could maintain the oil burner for supplemental or emergency use? And how would I control the two? Any input is appreciated.

 

[theoldwizard1]

Electric resistance heat ie EXTREMELY INEFFICIENCT ! You will cry when you get your electric bill for heating when the sun does not shine.

 

[chinboys]

Have you considered other electric based heaters?
Portable radient electrical units in baseboard, box, or parabolic shapes will heat you and not the air.

 

[larry4406]

Following along....

I have been thinking of a similar duct heater to temper incoming air for a range hood makeup air system.

 

[firebirdparts]

I haven’t done it, by my thoughts would be this:
1 if this is an experiment to size a heat pump, then good. You can easily math out everything you want to know by putting an hour meter on the heater and keeping track this winter. It’ll be a lot of electricity but you know that.

2. Afterward, You should be able to guess whether or not a heat pump will pay for itself. Heat pump performance is complicated and depends on the weather and all that, but hopefully you’ll have a conclusion. Maybe after the addition.

3: nobody with electric resistance heat would ever need oil as a backup. You would expect to keep resistance heat as a heat pump add-on. There could be electricity cost situations where that becomes interesting, but it would be odd. You may need the capacity but if you run both the air is going to get might hot.

 

[PCustoms]

Electric resistance heat ie EXTREMELY INEFFICIENCT ! You will cry when you get your electric bill for heating when the sun does not shine.

Its actually very efficient, as nearly all of the electricity is converted to heat.

But in most areas it's very EXPENSIVE.

 

[Jackfre]

Thermopride is recognized as the best oil fired furnace made. Yes, do get it serviced and do it now before the season really hits. If yours is an older HP it likely won’t heat below 40*f. What are the manuf specs on the current unit? Adding electric strip heaters to the mix is, imho, throwing good money after bad. Do your planning for the build, calculate the heat/cool requirements and go from there. You would need a very large solar system to make your plan pay out.

When it comes to putting in new high efficiency heat pumps like mini-splits when you all ready have a decent system my advise is not to change, but to add. Once the new mini-splits prove effective for you then you can make the plans to get rid of the oil. It‘s kind of the belt & suspenders deal, but having lived there, CT gets cold

 

[PCustoms]

I think people are missing the OP wants to leverage his available solar kW...

 

[theoldwizard1]

Its actually very efficient, as nearly all of the electricity is converted to heat.

True, but a heat pump is MUCH MORE efficient, because it just moves "heat" from one place to another.

But in most areas it's very EXPENSIVE.

Resistance baseboard is cheap and easy to install. Expensive to operate.

 

[theoldwizard1]

I think people are missing the OP wants to leverage his available solar kW...

You will cry when you get your electric bill for heating when the sun does not shine.

Also, the 2nd Law of Thermodynamics says you will lose a lot in converting DC electric from the solar array into chemical energy in the batteries, back to AC electrical energy.

 

[fitter30]

Solar panel power water heater

DC Water Heating Using Resistive Heating Elements

Alternative Energy Tutorial about DC Water Heating using solar power and how water can be heated up with DC electricty from a PV panel or array

www.alternative-energy-tutorials.com

After market electric strip heat. Want the heater close to duct size to have the most air over the elements. 3.41 btu per watt.

Warren SL10A 10 KW Electric Duct Heater 240/1/60 1 Stage 24V Control

Warren SL10A - 10 KW Electric Duct Heater 240/1/60 1 Stage 24V Control

voomisupply.com

 

[danski0224]

I just had solar panels installed and I’d like to utilize the electric power to heat my house. Because I plan on doing an addition in the near future, I don’t want to spend the time/money on a heat pump without knowing the exact size I will need. I haven’t decided on how big of an addition yet, but our two bedroom house is getting tight with two dogs, a new baby and a wife who wants another. I currently have a Spirit (Thermopride) oil fired 3 ton unit and they don’t offer electric heat or heat pump for my ahu. I know strip heaters are installed to supplement heat pumps in real cold areas. I’ve also seen electric duct heaters like THIS that seem pretty straight forward and easy to install, just curious if anyone has done it before? I’m also wondering if I should/could maintain the oil burner for supplemental or emergency use? And how would I control the two? Any input is appreciated.

You would need to do a load calculation on the space in question and then size the duct heater (and power supply) accordingly.

They are relatively easy to install. There are millions of them in duct systems.

What you should look into is a dual fuel system that uses a heat pump and your oil furnace.

You still need a load calculation and the thermal balance point.

The system would be controlled by a thermostat with dual fuel capability. That same thermostat could control those electric duct heaters.

 

[PoorUB]

I just had solar panels installed and I’d like to utilize the electric power to heat my house. Because I plan on doing an addition in the near future, I don’t want to spend the time/money on a heat pump without knowing the exact size I will need. I haven’t decided on how big of an addition yet, but our two bedroom house is getting tight with two dogs, a new baby and a wife who wants another. I currently have a Spirit (Thermopride) oil fired 3 ton unit and they don’t offer electric heat or heat pump for my ahu. I know strip heaters are installed to supplement heat pumps in real cold areas. I’ve also seen electric duct heaters like THIS that seem pretty straight forward and easy to install, just curious if anyone has done it before? I’m also wondering if I should/could maintain the oil burner for supplemental or emergency use? And how would I control the two? Any input is appreciated.

I feel I have to ask, are the solar panels large enough to get any reasonable electric heat load from them?

What size are the panels? How many Kw can you get from them?

I think I would leave the oil furnace in place for backup. It is there already and doesn't cost you a penny to leave it in place. There are several companies that sell electric plenum heaters for your application. It is fairly simple to control both. Most manufactures have plenum heaters with controls built in that will control both. It would not be very hard to do the control side, but it depends on what you buy.

 

[jlv03]

If you haven't had the chance to run your solar system through a full winter yet, my advice would be to do nothing and see where you land on actual production.

I have a spreadsheet where I track daily/monthly production and, let me tell ya, the winter months can be BRUTAL for actual watts produced. With a decent amount of snow, I can show you weeks where the overall average is not even single digits.

If you have an oil or even electric water heater, I'd put my money and focus there first before messing with duct heaters. A heat pump water heater can be almost as cheap or sometimes even cheaper than even natural gas. If you get a 240VAC hybrid model, you can certainly set it up to use the standard heating elements to burn off some kWh.

 

[dcg9381]

I think people are missing the OP wants to leverage his available solar kW...

Better have big system. The link was to a 10kW heater.
Thing about solar is that peak output, maybe a few hours a day (best case). If there are any clouds, power isn't terribly stable in terms of output. Fixed array in winter? I'm thinking it's not going to produce what it's rated for assuming you can keep it clear of snow.

It's different if the OP can "net meter" and has additional power credit "stored" with the utility. Then spinning that meter makes sense.

 

[KenC]

Also, the 2nd Law of Thermodynamics says you will lose a lot in converting DC electric from the solar array into chemical energy in the batteries, back to AC electrical energy.

I've often wondered why we need to. Seems fairly simple to design heat pumps driven by a variable speed dc motor. And DC resistance heat from battery should also be simple. Of course using both AC grid power and site-generated DC would be a challenge.

 

[theoldwizard1]

I've often wondered why we need to. Seems fairly simple to design heat pumps driven by a variable speed dc motor.

Most (all?) mini-split as well as some full sized heat pumps use "inverter technology". This means that the AC power coming in is converted to DC and then converted to 3 phase AC. (This is NOT the same 3 phase power that commercial buildings get. Lower voltage and the motor is designed to match this voltage. The variable speed is achieved by varying the frequency.)

Why all this "shuckin' and jivin'" ? 3 phase AC motors are the MOST EFFICIENT electric motors ! (Thank you Mr. Tesla !) It is only in the past 10-20 years that the cost of the elctronics has come down to the point of making this possible.

Brushed DC motor are probably the worst design in terms of efficiency.

 

[jlv03]

I've often wondered why we need to. Seems fairly simple to design heat pumps driven by a variable speed dc motor. And DC resistance heat from battery should also be simple. Of course using both AC grid power and site-generated DC would be a challenge.

As theoldwizard1 has said, no need for variable speed DC motors, the technology already exists to variable speed an AC one.

EG4 (and I'm sure others) do offer a mini split heat pump that can be directly powered by solar panels: https://eg4electronics.com/categories/high-efficiency-appliances/eg4-12k-hybrid-solar-unit/

 

[dcg9381]

EG4 (and I'm sure others) do offer a mini split heat pump that can be directly powered by solar panels: https://eg4electronics.com/categories/high-efficiency-appliances/eg4-12k-hybrid-solar-unit/

IMHO, this is a terrible idea. It does look like it connects direct to PV, but solar is way too unstable in general due to changes in sunlight.
You need to buffer through a battery/inverter.

Direct heat from solar works well. We do that for pools, and I've done thermosyphon systems for hot water. But it's not going to store enough energy to reliable heating.