Switching From Electric to Gas Backup Heat Pump Questions

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Old 06-13-11, 08:01 AM
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Switching From Electric to Gas Backup Heat Pump Questions

Hello all. I am in a house that is currently all electric (without an all electric discount). We've got two air exchange heat pumps that use electric heat as their backup heat source (I am in norther Ohio so I promise you that the electric backup runs). We're looking at a couple of different options to get our costs down for next winter.

One option is to run natural gas to the house and replace the backup electric resistive heat with a natural gas backup (we're also looking at wood heating, but that isn't related to my questions here).

Does anyone have any experience swapping between the two systems? The units are only 3-4 years old (in the house before we bought it), so I am hoping that we could just swap out the existing heating elements and air handler and continue to use the heat pump units. I think this would be as simple as taking the A coil out of the current unit and putting it in the replacement unit.

Any thoughts? We're trying to get this tackled this summer so that we can reap the benefits next winter.
 
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Old 06-13-11, 08:22 AM
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I'll let the HVAC pros talk about the mechanics of making the change. But, what is your current cost of electricity and the tougher question, how much electricity can you attribute to the heating load? Also, what would be the cost for gas.

Now, where is your air handler, basement or attic? If it is in the attic or even if just some of the ducts are up there you could be paying a huge penalty, air leakage. Take a look and see if the system was sealed. It will be obvious as it requires every seam to be foil taped or painted with duct mastic.

Fighting heating bills from both ends, heat loss and heat source, can be very productive.

Bud
 
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Old 06-13-11, 08:34 AM
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Originally Posted by Bud9051 View Post
I'll let the HVAC pros talk about the mechanics of making the change. But, what is your current cost of electricity and the tougher question, how much electricity can you attribute to the heating load? Also, what would be the cost for gas.

Now, where is your air handler, basement or attic? If it is in the attic or even if just some of the ducts are up there you could be paying a huge penalty, air leakage. Take a look and see if the system was sealed. It will be obvious as it requires every seam to be foil taped or painted with duct mastic.

Fighting heating bills from both ends, heat loss and heat source, can be very productive.

Bud
I agree that I need to check on the sealing. I know it wasn't done very well that is for certain (at least on the parts that I can see. Most of the attic ducting is flexible insulated ducting, but the drunk line is not insulated and a big chunk was exposed to cold attic air last winter. I need to address that this Fall.

We have two air handlers. One in the basement that services the basement and first floor, and one on the first floor that services the upstairs and one room on the first floor. The HVAC design for the house was very poorly done and the installation work wasn't a whole lot better.......
 
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Old 06-13-11, 10:15 AM
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It sounds like you have an opportunity to find some improvements with the installation and that will help with heat/ac and old or new system.

I tend to disagree with the HVAC practice of flex ducts and minimal insulation on exposed ducts in unconditioned spaces. IMO, The insulation needs to deal with energy loss/gain at wind chill rates which are far more extreme than just being hot or cold. R-40 to 60 in an attic and then R-6 on the ducts is a poor design.

Since your system is complex, there is also the potential for pressure balance problems which result in good air being forced out and bad air being pulled in. A normal home can exchange ALL of its air every one to two hours. A tight home will take just three hours. Tighter than that then requires some form of added air via an energy exchange process. Every supply duct needs access to a larger return area without going under doors or entirely across the house. Very few installations do a good job of balancing.

When you add gas for the back-up you will need to add venting. The other possibility would be gas heater/s and disable the emergency bu on the heat pump. The actual dollars being spent on emergency bu heat is still a number you should determine.

bud
 
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Old 06-13-11, 08:32 PM
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for conversion you would typically need a new a-coil depending on the design of current coil. Besides you would typically have to remove the refrigerant and then the coil from the lineset just to maneuver the coil around. To put a new coil in would not be that much extra over trying to reuse your current coil.
 
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Old 06-14-11, 05:38 AM
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Originally Posted by hvactechfw View Post
for conversion you would typically need a new a-coil depending on the design of current coil. Besides you would typically have to remove the refrigerant and then the coil from the lineset just to maneuver the coil around. To put a new coil in would not be that much extra over trying to reuse your current coil.
so I can keep the same heat pumps I have outside, and just replace the actual A coil in the new unit then?
 
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Old 06-14-11, 05:41 AM
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Originally Posted by Bud9051 View Post
It sounds like you have an opportunity to find some improvements with the installation and that will help with heat/ac and old or new system.

I tend to disagree with the HVAC practice of flex ducts and minimal insulation on exposed ducts in unconditioned spaces. IMO, The insulation needs to deal with energy loss/gain at wind chill rates which are far more extreme than just being hot or cold. R-40 to 60 in an attic and then R-6 on the ducts is a poor design.

Since your system is complex, there is also the potential for pressure balance problems which result in good air being forced out and bad air being pulled in. A normal home can exchange ALL of its air every one to two hours. A tight home will take just three hours. Tighter than that then requires some form of added air via an energy exchange process. Every supply duct needs access to a larger return area without going under doors or entirely across the house. Very few installations do a good job of balancing.

bud
Yes, there is certainly room for improvement without a doubt. I don't know that there is enough return area for one of my furnaces, but I'm also not really sure how to increase it given that all the system would now be a total nightmare to modify.

Can you recommend a good solution for sealing the rectangular ducting in the house? The little bit of ducting that is round and not insulated I figure I can just use mastic on. Not sure what do do with the rectangular though.

Oh and should I even worry about insulating the trunk line in the attic? We're getting ready to add a bunch of insulation to the attic (12" or so) so that might be enough?
 
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Old 06-14-11, 04:20 PM
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Originally Posted by bainbridgematt View Post
so I can keep the same heat pumps I have outside, and just replace the actual A coil in the new unit then?
that is correct... HP can stay, but new a-coil would be recommended
 
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Old 06-14-11, 08:27 PM
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Let me add that today's HP heat a lot better than even 5 years ago so even staying with a HP will give you more heat than the unit you have
 
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Old 06-15-11, 06:02 AM
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Originally Posted by airman.1994 View Post
Let me add that today's HP heat a lot better than even 5 years ago so even staying with a HP will give you more heat than the unit you have
Sounds like this is almost a no brainer.

Anyone have an idea on what I can expect to pay for the darn units? I'm debating between replacing these two units or going with a wood burning fireplace insert. The biggest problem is that there is no gas to the house at the moment (still waiting to hear back from the gas company on the cost to get that to the house).
 
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Old 06-29-11, 12:52 AM
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A good option in your case is to leave the air handler alone and have a hydronic coil installed upstream.

You'll have to get a gas fired boiler and related equipment installed.

If the air handler is replaced with a furnace, the indoor coil will have to be replaced as well and the heatpump will be rendered completely useless when backup is required.
 
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Old 06-30-11, 07:23 AM
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Well it sounds like they are going to have to do a main line extension to get gas to our house, so that won't be cheap. Looks like the wood burning insert might be the way we have to go.....
 
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Old 07-02-11, 11:51 AM
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Why not spend the money on super insulation?
Super insulation will save you money every year for ever.
 
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Old 07-03-11, 10:05 PM
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Originally Posted by Perry525 View Post
Why not spend the money on super insulation?
Super insulation will save you money every year for ever.
The insulation is a no-brainer and will of course get done regardless of the new heat source we add.
 
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Old 07-04-11, 01:06 AM
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If you insulate to Passive House standard (European not USA) you will only need 90% or thereabouts of your existing power to keep you warm to the existing standard. Why therefore spend a lot of money adding extra capacity that you will not use?
 
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Old 07-04-11, 10:45 AM
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Originally Posted by Perry525 View Post
If you insulate to Passive House standard (European not USA) you will only need 90% or thereabouts of your existing power to keep you warm to the existing standard. Why therefore spend a lot of money adding extra capacity that you will not use?
The issue isn't just extra capacity, the issue is also that the existing capacity costs a lot of money to run. If I can heat the house on wood alone and hardly have to use the electric then that is even better!
 
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Old 07-04-11, 11:48 AM
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The issue isn't just extra capacity, the issue is also that the existing capacity costs a lot of money to run. If I can heat the house on wood alone and hardly have to use the electric then that is even better!

If you burn wood, while it may cost nothing, it does have to be collected, dried, cut to size, stored and fead to the fire, all this may well loose its appeal when you get older.

Meanwhile, the fire will need to have a high output, large enough to heat an entire home on a cold winters night, plus hot water, a chimney, an air supply that does not result in your burning air that you have already paid to heat and one that does not create drafts, as you want to heat other rooms, distribution pipes, radiators with thermostatic valves, a back boiler with pump and thermostat, a well insulated tank for your hot water and an expansion tank. A great deal deal of expense and a lot of work, have you estimated how long will it take to pay for itself?
 
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Old 07-04-11, 06:42 PM
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time to pay 3-4 years.

all the work you speak of is outside the scope of this project.

This thread wasn't meant to discuss the merits between gas and wood. I'd prefer gas in the first place but with having pay for several hundred feet of main line extension it is likely not worth it.
 
 

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