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alochin 09-09-2011 08:10 PM

Upgrades for my old electric furnace?
I have an old electric furnace, Lennox model E11Q5-941-1P.
My house was built in 1976, and the furnace may be that age too.
Does anyone have documentation on this furnace?

I took pictures.
Whole furnace:
Wiring Diagram:

Everything is working fine, except my electric bill. Not too bad though, 20,000KWh/year for a 2900sqft house ($1600/y, thermostat at 68/day - 62/night). My fear is that as energy price increases (we have the lowest in the Nation, at $0.08/KWh), my bill will become outrageous.

I live in the Seattle area, Washington State.

I got a quote for a heat pump. The technician assessed my house first, and estimated my yearly electric bill at $2000 at 72F setting, so in the ballpark. He then estimated my savings at $900/y using a 3-ton two-stage 16SEER Amana system. Considering my actual consumption, I should save about $720 a year ($900*1600/2000).
The price for the Amana is 7000+tax. Payback will be beyond 10 years, so I am hesitant, considering the simplicity/reliability of my current system, and the complexity of a heat pump.

I also thought of just replacing the blower to a high efficiency blower, but that is non-sense, since the electricity that the blower is not using is actually dumped as heat, so I can consider my old blower as 100% efficient for my application (60% or so ventilation, the rest heat, which is what the furnace is for).

Any part I should be wary of failing soon in my system?

On the other hand, I am planning on installing a solar hot water system.
The system will use about 100sqft solar collector, which will collect a fair amount of heat, beyond what we need for hot water in the Spring to Fall months. The solar water tank will hold 140 gallons, with a set temperature at 180F. Assuming I will use it from 180F down to 120F (to leave some heat for showers), there will be 70,000 BTUs storage available for space heat.

How can I use that heat? Should I add a water coil in my furnace? Wouldn't that increase back pressure on the blower?

The blower has 5 speeds, but only the LO (for startup) and HI are used (if I understand the wiring diagram properly). Could I use one of the remaining settings (MED-HI) for solar heat, and only use electric heat when the solar tank is below 120F? Basically, the current electric heat elements would become backup heat. How could that be safely wired? Do I need a different thermostat, to call for solar heat first, then for electric heat when solar heat is depleted.

Thanks in advance for any reply/advises on this.
Because I am now replacing my roof (old house, needs repairs...), my finances will be tied for a while, so I have time to think about properly upgrading my heating system.

Have a great weekend!
Andre, from PNW.

REP 09-09-2011 08:48 PM

Since the Absolute Top Way to save money on a heater is to make sure(and I mean make sure with a manuel "J" )that it is the right size for your house.
If its too big then you pay extra every time it comes on,too small and you don't get warm.
The next thing that will save you money is to get that paid for heat into your house and back to the heater in the most effienct way.That requires a MANUEL "D".It is the only way.Repeat it is the only way.
After you get those things done ,,,,then you can look at heat pumps etc..
The day of just looking at things and coming out with a size and design is over ,,,,,,,ITS OVER.
Energy just costs too much and its getting worse and will continue to get worse.

alochin 09-10-2011 01:16 PM

Hi REP, thanks for you answer.
I agree that too big or too small is bad, between short cycling and runnig constant, it is important to properly size my system.
I am not sure I want to replace my furnace. It appears properly size, considering how it cycled last winter. It is working well so far, in the two years we have been here. My preference would be to keep it as back up heat, and use a more efficient system as my main source of heat, Basically re-using as much as I already have.

I think the problem with adding a solar hydronic coil will be sizing the coil. If I want to use water down to 140F, I will need approximately 140sqft of heat exchange area assuming 1000CFM air flow (3-ton at 400CFM/ton, so 1000CFM is a bit consevative). If I don't want to put too much static pressure on the blower, I will need something huge, likely carrying a huge price as well.
I had a few ideas building my own heat exchanger using fin-tubes like these:
but it quickly appears crazy. It would almost meet the BTUh requirement, but would pose a series of challenges and potential problems. the heat exchanger would be inserted inside the main duct. I abandonned this plan.
I am still looking for the right coil. As you said, proper sizing is the main challenge here.

I may also have a challenge in sizing the solar water tank.
Any idea and experience welcome...

bobelectric 09-10-2011 01:40 PM

35 years old?

alochin 09-10-2011 05:18 PM

Yea I hear you. That is why I initially got contractors to bid on a heat pump.

Here is the problem I am having: this is a plain electric system, no different in principle than the backup system on the heat pumps I have been quoted, except it has a proven reliability. Why replace it? Why can't we add up to it? I can replace the bearings of the blower, replace the relays with a sequencer, whatever wear part that will eventually fail ... but why replace the whole thing? It hasn't shown any sign of problem yet.
The contractor said that with our climate (Seattle), the heat pump will run on the heat strips for about 80 days (the coldest days), so for those 80 days I need heat the most, I will have replaced my working furnace with ... an exactly identical system ... for $8000 ??? Of course I don't know how long my 35 years old system will work, but then, I think of my co-worker's neighbor (read on...).

One of my co-worker has his neighbor having constant problems with a heat pump. He swears he will never get one. Then I wondered how long will my new heat pump last? Will it last its ROI (10+ years). If not, replacing my furnace becomes a loosing proposition.

Questions questions ...

My furnace has a dual return duct (one from each floor), so I am going to put a 5GEN5 coil downstream of the furnace, and one smaller 5GEN9 coil in each of the return ducts, upstream. 92,000 BTUh from a solar hydronic should make some difference.
The hot water will go to the 5GEN5 first, then to both 5GEN9 in parallel, so as not to dump too much heat on the blower.

alochin 09-11-2011 02:24 PM

Assuming 35% of my energy is used for space heating, 15% for hot water, that is 10MWh/y for heating (half of the 20MWh I use yearly).
We have 3.5 sun-hour/day yearly average in Seattle.
We receive an average of 3.5KWH/m2/day in Seattle, equivalent to 0.3KWh/sqft/day.
With a 100sqft collector, 50% efficient, I will collect up to 365*100*0.3/2= 5475KWh/y. 50% of that may be usable, so about 2.7MWh = $219/year.

15% hot water already costs $240/year, so that tells me the solar system should be used exclusively for hot water.

1. There will be very little extra heat usable for space heating. Use solar for hot water usage only (hot water used all year long).
2. Cost of solar hot water system should be kept below $2000 to have reasonnable ROI. That means DIY pex collector, DIY tank, as described here:
3. $700 yearly savings on space heat looks pretty good now. I wish I could learn how to install it myself, but considering the reliability of a heat pump mostly depends on the quality of installation, I am hesitant to go that route.


JackDidley 09-11-2011 07:09 PM

I am not a pro, but I sort of understand your situation. My 20 year old gas furnace has worked perfectly all its life. Last winter when the blower started making bearing noise, my HVAC friend really wanted me to get a new system thats efficient. My old one has no circuit boards and is very simple to maintain. Replaced the relay and transformer at the same time as the motor so that stuff should last a while. I recently had AC problems, so I had him replace it with a heat pump. This winter I should be able to get efficiency from th HP and use the gas furnace when it gets real cold. I just hate to replce something that has worked so well.
