Variable speed heating systems

[JoeyD]

I am in the process of replacing my house heater and was wondering if it is worth while getting a unit with a variable speed fan as opposed to a more traditional heater if I am primarily heating with my wood stove? One guy I got a quote from doesn't think it is worth the extra money but I have a family member who loves his system.

My question is based on the fact that my stove heats my house any where from 12 to 20 hours a day. Does the fan on these things run when my house is 70 degrees and my thermostat is set at 66? If it does I am thinking it might not be a benefit trying to recirculate the stove heat thru the cold duct work. Right now for the most part my heat does not even turn on unless it goes below 15 degrees outside while the stove is running.

How much of a benefit is it when I am running my air conditioning? Right now my fan runs at full speed 24/7 while the air is on.

Any thoughts or knowledge on this is appreciated.

 

[titleist1]

What I have seen with the variable speed systems is the AC is run at high speed in summer and the heat is run at the lower speed in winter. Some folks feel that having the fan on the higher speed in winter makes their house feel cooler even if the 'stat temp is the same.

Even if the furnace is not kicking on due to your wood stove, if you have trouble circulating the heat from your wood burner evenly throughout the house then running only the fan on the furnace unit at its low speed setting may help distribute the heat and eliminate hot rooms and cold rooms (or at least minimize the temp differences).

 

[heat seeker]

Mine is a three speed system - I like the quiet operation normally, but when the need arises, it will move some serious air, but makes noticeable noise. Supposedly there is a savings in electricity, but the payback is probably long. If the price differential isn't great, I'd go with a multi-speed system again. There may be other benefits with a more expensive system, too, such as a multi-speed compressor, which is quieter and more efficient. Your utility may offer rebates on more efficient systems; mine paid me several hundred dollars.

My AC costs me less than $2 a day in the hottest weather, far less than my window units cost to run.

 

[peakbagger]

I used to do HVAC systems for offices and conference rooms occasionally and converted over a few systems to VF drives, I found that I could usually get away with higher summer settings and lower winter settings by getting rid of the drafts from the registers. I am not trying to be sexist but the females in the room tended to be a lot more sensitive to drafts from registers and their response would be to crank up the heat.Ninety percent of the time the fans ran on low with far less drafts and the systems were a lot quieter, plus the VF had a ramp programmed in so there was no startup or shutdown noise

 

[titleist1]

I used to do HVAC systems for offices and conference rooms occasionally and converted over a few systems to VF drives, I found that I could usually get away with higher summer settings and lower winter settings by getting rid of the drafts from the registers. I am not trying to be sexist but the females in the room tended to be a lot more sensitive to drafts from registers and their response would be to crank up the heat.Ninety percent of the time the fans ran on low with far less drafts and the systems were a lot quieter, plus the VF had a ramp programmed in so there was no startup or shutdown noise

Do they offer VF systems for residences now? I thought they were only in the bigger commercial systems. I guess I mistakenly thought the OP was asking about simpler two or three speed fans systems, not variable frequency drive systems.

 

[peakbagger]

No idea if any household systems use VF drives, for one thing 3 phase vf drives are far less expensive then sngle phase drives so the economics may not be there. Then again my mini split has 3 speeds and a soft start for some operations so I guess its up to the manufacturer.

 

[woodgeek]

Folks like the variable speed because instead of 'kicking on' and off suddenly, it slowly ramps up and down making it much less noticeable and less likely to wake you up (if you are a light sleeper). The ECM motor also uses less power to move the same air, resulting in somewhat lower bills over time. It also allows you (or an HVAC tech) the tweak performance....AC often gives better dehumidification at lower cfm, so you can optimize your AC function, and maybe run comfortably at a higher setpoint (and lower humidity) saving more $$.

You will only circulate wood heat IF your ducts are very well insulated or in the conditioned space, but if you do, the variable speed will do it at a low speed (if you want) almost silently and at much reduced power consumption.

FYI, I have a variable speed blower....and I like it.

 

[ewdudley]

.AC often gives better dehumidification at lower cfm, so you can optimize your AC function, and maybe run comfortably at a higher setpoint (and lower humidity) saving more $$

Exactly so. Unfortunately there's a sad history in the AC industry of increasing EER ratings by delivering higher flows of cooled humid air, which is air cooling, not air conditioning. ECM fanspeed control can give the operator the means to achieve comfort. (Sorry if somewhat off topic.)

 

[semipro]

AC often gives better dehumidification at lower cfm, so you can optimize your AC function, and maybe run comfortably at a higher setpoint (and lower humidity) saving more $$.

Exactly so. Unfortunately there's a sad history in the AC industry of increasing EER ratings by delivering higher flows of cooled humid air, which is air cooling, not air conditioning. ECM fanspeed control can give the operator the means to achieve comfort. (Sorry if somewhat off topic.)

It seems like installation of a humidistat in residential systems would make sense.
I don't quite understand why they're not used to adjust compressor and fan speed and run time to optimize "conditioning".

This would also help compensate for the "bigger is better" philosophy that some HVAC contractors have which may result in poor de-humidification.

 

[AK13]

I don't know if I am understanding the OP or not. By "house heater" I assume we are talking about a forced hot air furnace. I think that a variable speed fan is probably worth it if that means that you are getting a unit with ECM motors. ECM motors are 30-50% more efficient than traditional motors even if you run them both at full speed.

You aren't telling us how much of a cost premium the better unit is. What brands and models are you considering? Are you replacing your A/C condensing unit also? That is something to consider if its an older unit. Now might be a good time to upgrade the whole system and convert to R-410a.

 

[JoeyD]

One contractor quoted $1100 to move from 92% efficiency to 96.7% . With each visit from a contractor I learn something new so I scheduled a fourth guy to come out Monday. This is a Carrier. I am still trying to figure out what is best for me instead of someone telling me what they want to sell me. Today a guy came told me he won't put a high efficiency in my attic because the condensate could possibly freeze in an unheated space like my attic so he recommends an older 80% unit that vents thru a chimney in the roof. After an internet search I found there is some merit to that, so now I have to go back to one other guy I was considering and ask him his opinion and how he plans to deal with it. The last guy that came did the most through inspection of my home so far which has me leaning toward him and the 80% attic furnace with a high 96% in the basement. When he left I decided to call one more guy and hopefully I can decide next week.

I do appreciate the responses and since posting I have learned quite a bit. I just have to be careful and keep the facts straight and try to not confuse myself so I don't make a mistake. In total it looks like the two furnaces, and the hot water heater will come in between $10,000 and $12,000. It really seems to be more to important to pick the right installer more so then the system.

One other thing I need to consider is the rebates that range from $800 to $4300 depending efficiency.

 

[heat seeker]

Would you really be using the AC in freezing weather? The condensate drain has a trap in it that could freeze, but plastic pipe could probably take it. My unit is high efficiency with a condensate drain with trap, and it's survived 6 winters so far. It is in the unheated and well ventilated attic. It's cold up there! I think that guy is blowing smoke.

 

[woodgeek]

Would you really be using the AC in freezing weather? The condensate drain has a trap in it that could freeze, but plastic pipe could probably take it. My unit is high efficiency with a condensate drain with trap, and it's survived 6 winters so far. It is in the unheated and well ventilated attic. It's cold up there! I think that guy is blowing smoke.

A condensing burner WILL make condensate in the winter too, as a product of combustion, unlike a AC/heat pump.

 

[heat seeker]

That makes sense! I wasn't considering a condensing burner.

 

[fbelec]

if you plan on being in the house for a while and not moving and running a wood stove i would think that paying more for a higher eff. heater would be throwing money out the window. you got to look at the difference in money saved burning a 80% to 92%. 12% of next to nothing burnt because you are running a wood stove is wasting money. the down side of a ecm motor is when they go they are very expensive to replace. personally i haven't seen one last more then 15 years normally 10 years. and most times when it's gone it's the pc board inside it that go's and that can't be replaced in the field.

 

[semipro]

It really seems to be more to important to pick the right installer more so then the system.

One question you might ask is for them to show you the "Manual J" calculations for your installation.
Pass on the ones replying with blank stares.

There were many reports of frozen exhaust pipes from condensing systems this year with all the cold temps. Consider carefully how you might deal with that on your installation.

 

[JoeyD]

Thanks semipro. I Googled "Manual J" and found another reliable contractor that covers my area to give me an estimate. Once I have all the estimates in I will narrow things down and start asking specific questions including the freezing issue.

I am getting a nice education on gas furnaces and their installation.

Also:

if you plan on being in the house for a while and not moving and running a wood stove i would think that paying more for a higher eff. heater would be throwing money out the window. you got to look at the difference in money saved burning a 80% to 92%. 12% of next to nothing burnt because you are running a wood stove is wasting money. the down side of a ecm motor is when they go they are very expensive to replace. personally i haven't seen one last more then 15 years normally 10 years. and most times when it's gone it's the pc board inside it that go's and that can't be replaced in the field.

The high efficiency heaters are 96.7% so that is quite a difference over the 80% system. As far as wood heat, I plan to use it as much as possible but also have to look at it from the perspective of one day not being able to rely on it. On top of that my house is an old farm house broken up into smaller rooms. The wood stove works well until it goes below 20-25. At that point I have to run my heating system along with the wood stove.

Also, I am the only one in the house that can maintain the wood stove enough to be able to rely on it to keep things warm. If I'm not here the furnace runs.

 

[AK13]

Ugh, furnace in an unheated attic is really lousy. Very bad for efficiency. That means holes in your thermal barrier every place that you have a supply and return register. And it means that any duct leaks are going straight outdoors, not to mention the heat loss from the unit itself and the ductwork. More than 80% vs. 96% efficiency my focus would be on very well insulated and well sealed ductwork.

Honestly that is just a really bad set-up. But the only way to fix it would be an extensive reconfiguration of your heating system to get the equipment out of the attic or insulating your roof. Both are probably in the 10's of thousands of dollars.

Just to be sure your insulation is on the floor of the attic, not at the roof, correct?

 

[blades]

When I replaced my furnace some 5 years ago the 96% units were a very large chunk of change more than the 92% range units. Now my 80 % which worked ok was of the standard combustion exhaust configuration for older furnaces, combustion air from basement- exhaust out flue. So that means it was pulling air in through any little leak possible. by going to the 92% and sealed combustion unit I installed that infiltration of cold air was considerably reduced. I would have gone with a sealed combustion hot water unit as well but the prices were so outrageous that the unit would self destruct long before the payback took place, I went with a forced exhaust type because of the cost but not a sealed combustion unit. A word to the wise on these type hot water heaters you need to install ( if it is not included with the unit) a back draft damper on the exhaust. Might have of been a screw up by the installer ( not me) The difference in the shoulder season bills was quite apparent after I installed it. So it is going to be more than adequately paid for over the course of this winter ( it was a cost $50 with shipping. had a devil of a time finding a 3" one)

 

[xman23]

I have a pilot lite that blows out during ignition. A 40 year old gas hot air. The guys selling us a new one said just fix it. the payback would be long and the were huge chimney issues.