Heat pump miracle!

[dooleysm]

Right after college I lived in an apartment that had a heat pump. It had to get a good deal colder than 38 for the backup electric heat to kick on. I'm thinking down in the low 20's. This is according to the light on the thermostat that indicated the backup heat was on. I assume that light wasn't lying.

I have a geothermal heat pump in our house now, and it has to get cold and stay cold for several days for the backup heat to come on. Based on the electric bills, I agree with what the light on the thermostat is telling me.

$160/month for electric in the winter doesn't seem too out of line for a heat pump in a 1600 sq. ft. house to me. Could be other things raising that too, like longer, hotter showers, causing the water heater to work more, reduced daylight causing more electric light usage, etc.

I read up on those programmable thermostats and they weren't really recommended for geothermal. I didn't pay attention to the recommendation for regular heat pumps, but I assume it's the same as geothermal. Heat pumps are good at maintaining temperatures, but not as good at raising them. Since they blow out warm air, as opposed to hot air like a gas furnace, it takes a long time to raise the temperature.

 

[Sigarms]

A heat pump will work well below 38 degrees.

There are MANY variables that can affect a heat pumps performance.

That said, a heat pump will lose it's heating capacity the colder it gets outside, but it's nothing that usually can't be found in the manufacturers specs.

Looking at one 24,000 BTU model in particular, at 17 degrees outside, the unit is only "putting out" 11,900 BTUs. One reason to have strip heat.

The biggest issue between a heat pump and gas furnace is the discharge air temp at the registers. A R-22 heat pump in the heating mode will usually put out air at a temperature under 98.6 degrees at the register, so if the air hits a persons skin, it actually feels "cool" because the discharge air is less then the body temperature. A gas furnace on the other hand, will put out an air temp over 100 degrees, so when that air hits the body, the air feels warm.

Any HVAC service tech worth his weight will NEVER replace a gas or oil furnace with a heat pump for anyone who is over age 60!

Get an older person who is used to gas or oil and they go heat pump, does not matter what the t-stat says (or your own thermometer), it's still to cold

You know what's really funny? Know what the biggest HVAC market is in Montreal? Heat pumps. Electric is dirt cheap there.

Buy a programable t.stat. & set the temp. back to say 65 etc, deg

That can be debatable if you then have it set to, say 72 or 73 degrees because then you'll be running your strip heat to get it to the set temp (I'm assuming it'll be warmest during the day).

i bought a place last January, that has a practically new high eff gas furnace, along with a @20 year old ac system, i am sure i will have to replace the ac system long before i do the furnace, but had never thought about being able to do it this way? I know it probably cost considerably more

Replace the AC with a heat pump. Price wise, a heat pump should only cost a little more than an A/C system. You already have the biggest cost difference taken care of, the gas furnace. This is where you get the big price difference between a heat pump and a "duel fuel" system, the gas furnace. Then again, also depends on what kind of gas furnace. 80% non variable speed, 90% non variable speed, 80% variable speed two stage, 93+ variable speed two stage. The order is usually the order of price as well (least expensive to the most expensive).

One reason why I racked my brain out on my first floor system. Had a Lennox Pulse furnace with A/C. Wanted to go with duel fuel, however I had to go with a 95% two stage variable speed furnace which was the most expensive (I LOVE variable speed, and had to use a 90 plus furnace for PVC venting). Problem was, I couldn't justify the price difference on that gas furnace compared to a plain variable heat pump system. That's why I put in a set of gas logs on the first floor for back up heat. First set of gas logs I've ever owned, and love them for the heat they supply. I can take the first and second floor up to 70 degrees from 65 without any system running (each floor has it's own system) in only three hours when it's 29 degrees outside (my wife just loves it when I get in the "experimental" mode with the thermometer). Price difference between those logs and the gas furnace I was looking at? Over 1 grand for the equipment alone.

I'm just waiting to see if Ken is right about the fuel consumption on those gas logs!

 

[heehaw]

i have always heard, that if you raise the temp on the thermostat by 3 or 4 degrees at one time, on a heat pump, the strip heaters will kick in to assist?? so bringing the temp back up, could be rather expensive.
heehaw

 

[kenmac]

I'm just waiting to see if Ken is right about the fuel consumption on those gas logs!

I hope I"am right also. All I did was the math. Then again, I never was good at it

 

[kenmac]

i have always heard, that if you raise the temp on the thermostat by 3 or 4 degrees at one time, on a heat pump, the strip heaters will kick in to assist??

That's about right. If you have an old mercury type t.stat all you have to do is take the cover off & watch the second bulb of mercury move as u raise the temp.

 

[kenmac]

The biggest issue between a heat pump and gas furnace is the discharge air temp at the registers. A R-22 heat pump in the heating mode will usually put out air at a temperature under 98.6 degrees at the register, so if the air hits a persons skin, it actually feels "cool" because the discharge air is less then the body temperature. A gas furnace on the other hand, will put out an air temp over 100 degrees, so when that air hits the body, the air feels warm.

Any HVAC service tech worth his weight will NEVER replace a gas or oil furnace with a heat pump for anyone who is over age 60!

Get an older person who is used to gas or oil and they go heat pump, does not matter what the t-stat says (or your own thermometer), it's still to cold

I took out my old gas furnace once & installed hydro heat using a 65,000 BTU gas water heater & a water coil in a air handler.My wife was always complaining about not being warm enough & she isn't 60 . Long story short. I got tired of sleeping with the dog. So, I installed a 90+ gas furnace . Now she is happy & I am also. When mommy isn't happy . No one is happy

 

[KentT]

A heat pump will work well below 38 degrees.

There are MANY variables that can affect a heat pumps performance.

That said, a heat pump will lose it's heating capacity the colder it gets outside, but it's nothing that usually can't be found in the manufacturers specs.

Looking at one 24,000 BTU model in particular, at 17 degrees outside, the unit is only "putting out" 11,900 BTUs. One reason to have strip heat.

The biggest issue between a heat pump and gas furnace is the discharge air temp at the registers. A R-22 heat pump in the heating mode will usually put out air at a temperature under 98.6 degrees at the register, so if the air hits a persons skin, it actually feels "cool" because the discharge air is less then the body temperature. A gas furnace on the other hand, will put out an air temp over 100 degrees, so when that air hits the body, the air feels warm.

Yes, you are technically correct -- they will work, they're just not efficient at those lower temps. In your example, that heat pump would likely be grossly oversized in cooling capacity to keep the same house warm in winter. Note that MANY HVAC systems are actually oversized by the installer just to minimize complaints and callbacks -- if they don't really try to model your specific house, the techs will often rely on "rule-of-thumb" then go to the next larger size just to keep the homeowner from complaining -- leaving the homeowner with higher utility bills than necessary, and possibly other side-effects of having an oversized cooling system...

Many of the "Energy Star" certs and rebates for dual-fuel require thermostats both inside and outside, and require the secondary furnace to kick out at 40 degrees, and many systems are set to kick in at 38...

I make no pretense of being an HVAC guy, but I've been researcing these systems (including geothermal) fairly extensively for building my retirment home. I was orginally thinking log home (machined logs) and ground-source heat pump, but have decided to go timberframe/SIPS because I can heat/cool the same square footage with dual-fuel at about the same operating costs, while the savings on the HVAC system essentially offset the added costs of the SIP construction method. This will give me the wood and beams I want inside without the maintenance hassles of logs outside...

 

[Sigarms]

Note that MANY HVAC systems are actually oversized by the installer just to minimize complaints and callbacks -- if they don't really try to model your specific house, the techs will often rely on "rule-of-thumb" then go to the next larger size just to keep the homeowner from complaining

I'd respectfully argue that many systems are oversized because a load calculation wasn't done on the house to determine the proper heating and cooling needs. Guys would rather guess larger.

Many of the "Energy Star" certs and rebates for dual-fuel require thermostats both inside and outside, and require the secondary furnace to kick out at 40 degrees, and many systems are set to kick in at 38...

Curious if you found that info on energystar.gov? Not sure what a secondary furnace is unless your talking 2nd stage of heat, which is what would "kick in" at 40 degrees (usually the norm due to defrost cycle on the heat pump which Ken spoke of). Idea is the heat pump handles first stage of heat down to 41 degrees, then when it hit's 40, second stage (gas furnace) kicks in. Now, if you've got a two stage gas valve in the furnace, you've got three stages of heat.

I had three gas/ac systems when I bought the house. First system I changed out was the third floor (attic instal) from yet another Pulse 90 plus furnace-A/C system to a 80%, two stage variable speed furnace with heat pump. Going duel fuel on that first system change out saved me at least 35% on my LP bill for the year.

Keep in mind, I live in North Carolina, not upstate NY.

Geothermal is the way to go if you can afford the up front costs IMO.

 

[MarkV]

Now that we have some HVAC pros in the conversation I would like to ask about load calculations on a house. It seems the times I have had a system installed the tech takes a look around and say 'yep, 3.5 ton'.

So, is there a source that can show a homeowner how to do a load calculation? Also if you ask a contractor about a load calculation what type of questions should you ask to see if one was done properly.

MarkV

 

[dooleysm]

We have vent free propane logs on our first floor, along with a geothermal heat pump. We got a good deal on the logs/cabinet, which were a showroom model. We wanted a non electric backup in case of a wintertime power failure (which we have yet to experience, thankfully). We have an open floorplan with the kitchen, dining area, and living room all in one big area. There is an upstairs balcony overlooking the living room, so lots of the first floor heat escapes up there.

That situation makes for some cold winter mornings in the kitchen. Our gas logs are in the living room, so it is really nice to come out on a cold morning and flip on the logs while you're drinking your coffee and eating breakfast. They can raise the temp in the kitchen by 2-3 degrees in an hour, while making it VERY warm upstairs.

The only other propane appliance we currently have is our oven/range. Our propane is supplied by 2 100# tanks. We use less than 200#/year, at a current price of $65/100# tank (the propane folks just swap out the whole tank). I don't know how much the oven/range consumes, but I think we use ours quite a bit more than the average person. Lots of canning and baking.

 

[kenmac]

Now that we have some HVAC pros in the conversation I would like to ask about load calculations on a house. It seems the times I have had a system installed the tech takes a look around and say 'yep, 3.5 ton'.

So, is there a source that can show a homeowner how to do a load calculation? Also if you ask a contractor about a load calculation what type of questions should you ask to see if one was done properly.

MarkV

see if you can locate or try to google a manual J. Here's a start from google...........Load Calculations

 

[KentT]

I'd respectfully argue that many systems are oversized because a load calculation wasn't done on the house to determine the proper heating and cooling needs. Guys would rather guess larger.



Curious if you found that info on energystar.gov? Not sure what a secondary furnace is unless your talking 2nd stage of heat, which is what would "kick in" at 40 degrees (usually the norm due to defrost cycle on the heat pump which Ken spoke of). Idea is the heat pump handles first stage of heat down to 41 degrees, then when it hit's 40, second stage (gas furnace) kicks in. Now, if you've got a two stage gas valve in the furnace, you've got three stages of heat.

I had three gas/ac systems when I bought the house. First system I changed out was the third floor (attic instal) from yet another Pulse 90 plus furnace-A/C system to a 80%, two stage variable speed furnace with heat pump. Going duel fuel on that first system change out saved me at least 35% on my LP bill for the year.

Keep in mind, I live in North Carolina, not upstate NY.

Geothermal is the way to go if you can afford the up front costs IMO.

Won't disagree with you on the "oversizing issue" -- it seems that part of the problem is that many of the HVAC guys either don't truly do load calculations, or that they can't/don't model a lot of the recent changes in home construction such as super-insulation (via SIPs, ICFs, etc.), thermal-mass in log walls or ICFs, passive-solar, new Low-E window technology, etc. Then, as you state, they'd likely intentionally err on the "high side"... the result is the same -- overcapacity. This is especially important in either timberframe or log construction, where the over-capacity may not do a good job of controlling humidity, in addition to not being the most energy efficient solution...

I don't recall where I saw those numbers about the second heat source control -- it was when I was looking at rebates based on Energy Star certs for the HVAC...

I'm planning on building in East Tennessee, likely not a lot different from where you are, especially if you're in the Blue Ridge foothills. Perhaps a bit cooler in the summer, but still high humidity, and relatively mild winters. Luckily I'll be about 50-60 miles from Oak Ridge, TN, so a lot of the research they've conducted there should translate to my location quite well...

I'm certainly not going solar-electric, though I'm planning to do some passive-solar design work (siting, windows, etc.) and am still looking into the potential of solar hot water. The ROI on that one might work (electric doesn't, especially on TVA-supplied grids), when combined with on-demand propane fired hot water heater, and in-floor radiant heat in the slab of the full-walkout basement. I'm still 2+ years away from building, so I'm still in the research mode, and this technology is changing fast...

 

[KentT]

We have vent free propane logs on our first floor, along with a geothermal heat pump. We got a good deal on the logs/cabinet, which were a showroom model. We wanted a non electric backup in case of a wintertime power failure (which we have yet to experience, thankfully). We have an open floorplan with the kitchen, dining area, and living room all in one big area. There is an upstairs balcony overlooking the living room, so lots of the first floor heat escapes up there.

That situation makes for some cold winter mornings in the kitchen. Our gas logs are in the living room, so it is really nice to come out on a cold morning and flip on the logs while you're drinking your coffee and eating breakfast. They can raise the temp in the kitchen by 2-3 degrees in an hour, while making it VERY warm upstairs.

The only other propane appliance we currently have is our oven/range. Our propane is supplied by 2 100# tanks. We use less than 200#/year, at a current price of $65/100# tank (the propane folks just swap out the whole tank). I don't know how much the oven/range consumes, but I think we use ours quite a bit more than the average person. Lots of canning and baking.

Are you running reversible ceiling fans. I know lots of people with cathedral ceilings who run them 24x7x365. They'll push the heat down from the roof, and if you run them in "updraft" mode they really don't make it feel drafty...

Thanks for the info on your propane system -- I'll have to use propane also, and the development requires a buried tank -- partially for aesthetics, but also forest fire hazard in the woods.

Plus, I'm so remote back in the woods, that I'll likely install a backup generator. When rural lines go down, either from ice or limbs, sometimes you're down for a day or two or worst case, much longer...

 

[dmccarty]

We used a construction design book written by Joe Lstiburek. He has books written four climate areas of the US. The books have design details for those climates for homes with brick veneer, various other sidings, crawl spaces, slabs, etc. I highly recommend that if one is building their own house to read Lstiburek's books for your climate and spec his designs as appropriate into your house.

I have not been to the website in years but they used to have quite a bit of info for free. Building Science Consulting

Later,
Dan

 

[dooleysm]

I do have a ceiling fan in there, but have never changed it from blowing down, mostly because it's a pain to get to. I'm going to stew on that a while and see if I work up the time and energy to flip that switch. I generally turn it on when I have the gas logs on though, and it is drafty, but it's blowing down pretty warm air, so it's not bad. It's not unusual for it to be above 80 upstairs after a couple hours of operation.

 

[KentT]

I do have a ceiling fan in there, but have never changed it from blowing down, mostly because it's a pain to get to. I'm going to stew on that a while and see if I work up the time and energy to flip that switch. I generally turn it on when I have the gas logs on though, and it is drafty, but it's blowing down pretty warm air, so it's not bad. It's not unusual for it to be above 80 upstairs after a couple hours of operation.

The ceiling fan, when reversed blows the cooler air from the first floor up into the peak of the house, gently pushing the warmer air down the outside walls. I think if you try it, with the fan on lower speeds, you'll like the results. Because the air from the fan isn't blowing down directly on you, and the fan is running slowly, you don't feel the drafts. Instead, it's like a reverse of the natural convection of warm air rising... you notice the temp difference, without noticing the air movement itself. (Running it on a low speed is key.) Otherwise, the warmest air tends to stay trapped up in the very peak of the roof... above your head even when on the second floor.

Some really high cathedrals, in timberframes especially, will use two ceiling fans -- one up in the very peak, used only in the winter to push the heat down to a lower fan that will spread it out into the rest of the house. Then, they run them blowing down, on low speed, not up... this is a bit draftier, but it spreads the heat around. I'm planning a 1.5 story, so I won't have 30+ feet ceilings to contend with.

 

[KentT]

We used a construction design book written by Joe Lstiburek. He has books written four climate areas of the US. The books have design details for those climates for homes with brick veneer, various other sidings, crawl spaces, slabs, etc. I highly recommend that if one is building their own house to read Lstiburek's books for your climate and spec his designs as appropriate into your house.

I have not been to the website in years but they used to have quite a bit of info for free. Building Science Consulting

Later,
Dan

Good link, thanks! While I'm not building it myself, I'm having to educate myself in order to put it in the GC's contract, since I won't be onsite much while it's being built... I wish I could, but I simply can't!

 

[Sigarms]

see if you can locate or try to google a manual J. Here's a start from google...........

Ken, Ken, Ken....

Haven't you ever learned?

Stand facing the house, directly next to the front doorway. Hold your arms out touching the tips of your thumbs together with the other eight fingers sticking straight up, just like you're making a "field goal".

Walk back from the house, counting your steps. When the house is able to "fit" between" your interior fingers, take the amount of steps you took to fit the house between your fingers and mulitply it by 12,000. Take that new number and divide it by the amount of people living in the house. Take that new number and multiply it by the number of cars the family owns, then take that new number and multiply it by the amount of windows the house has. Add 800 for each pet the family owns.

You now have your load calculation!

You would be surprised.

 

[kenmac]

Ken, Ken, Ken....

Haven't you ever learned?

Stand facing the house, directly next to the front doorway. Hold your arms out touching the tips of your thumbs together with the other eight fingers sticking straight up, just like you're making a "field goal".

Walk back from the house, counting your steps. When the house is able to "fit" between" your interior fingers, take the amount of steps you took to fit the house between your fingers and mulitply it by 12,000. Take that new number and divide it by the amount of people living in the house. Take that new number and multiply it by the number of cars the family owns, then take that new number and multiply it by the amount of windows the house has. Add 800 for each pet the family owns.

You now have your load calculation!

You would be surprised.

Joe , I have never heard that 1. I told you I'am not very good at math & you just gave me a formula with to many calculations. It's still much easier than the manual J...... This is the formula I used when I took the HVAC Exam.... I think it was 1 ton for every 500- 600 sq ft . I like it better than your's & the manual J

 

[Sigarms]

Joe , I have never heard that 1.

Say it with a straight face without bursting out laughing, you'd be surprised how many people look at you with eyes wide open, writing down notes

It's still much easier than the manual J......

First class, doing it by hand, took me longer than I'll ever admit to (in my defense, manual D as well the same day, which was pretty much the whole day come to think of it) Computers can be a good thing as long as you know the garbage you're entering.

I think it was 1 ton for every 500- 600 sq ft . I like it better than your's & the manual J

Just watch out for that R-value and window surface area, it can be a killer