ECM vs Hi Eff with wood fireplace and HRV

[tranelch]

I have read enough of this forum (and learned a lot in doing so) to understand that "fuel efficiency" trumps ECM for overall energy consumption in most situations, but I wonder about our specific situation. We have a well-sealed house with southern exposure, a heat pump, and a wood-burning fireplace. The furnace never runs in the fall and spring (heat pump), and usually only when the fire gets low at night during the winter. I think our main concern is circulating the fresh air from the HRV and the heat from the fireplace.

If we have the choice between 90% efficient ECM furnace, and a 95% efficient non-ECM, would the higher efficiency still be preferable over the ECM motor? Also, please let me know if my logic is off.

Thanks,
Chris

note: I am asking the question here because I specified (and my HVAC contractor bid) a 90%+, ECM furnace to meet energy star rebate requirement on a new home, I got a 95% efficient non-ecm motor. I fear my contractor may have some difficulty giving an unbiased opinion.

[badtlc]

I'm surprised its not a 95% WITH a variable speed blower. The added efficiency on the blower would be good if you plan on keeping the blower running 24/7 or for extended periods to help even out the heat distribution in your house from the fire place. Whether that would balance out in your situation by giving up 5% AFUE all depends on electric rates, gas rates, and plan of usage.

[hearthman]

Is this a typical open hearth fireplace or an EPA certified hybrid half fireplace/ half woodstove? Big difference.

[tranelch]

Is this a typical open hearth fireplace or an EPA certified hybrid half fireplace/ half woodstove? Big difference.

It is EPA certified (Quadrafire).

[tranelch]

I'm surprised its not a 95% WITH a variable speed blower. The added efficiency on the blower would be good if you plan on keeping the blower running 24/7 or for extended periods to help even out the heat distribution in your house from the fire place. Whether that would balance out in your situation by giving up 5% AFUE all depends on electric rates, gas rates, and plan of usage.

Thanks for the response. My contractor tried to tell me at one point that it did have an ECM motor, but I see no mention of it in the specs (it is an Amana GMH950...). Would we need to run the blower 24/7 to get the full benefit of the HRV as well? It doesnt seem like that unit (Broan Guardian) would be powerful enough to circulate the air throughout the house.

Thanks again,
Chris

[beenthere]

Its a 2 stage multispeed furnace.

It is not an ECM/VS blower.

The H in the model number indicates a multispeed blower.

If it was a variable speed blower, then the H, would be a V.

Amana has 95% AFUE VS blower furnaces.

Talk to your dealer.contractor about it.

[DanW13]

By having a ECM blower motor you will save a tremendously on the electric side of things running the blower with a ECM vs. a multi speed. I run my blower 24/7 with a ECM blower and I think it only cost me about $6/month just to run the blower on the furnace which translates to pennies a day. IMO in your situation with a wood stove and HP along with a gas furnace you would do ok with a 90% with the ECM blower motor.

[teddy bear]

An "Air cyclier" is an alternative to a VS furnace fan. This device has an adjustable timer that cycles the fan on schedule that monitors the fan operation. After an adjustable time of fan "off", the cyclier operates the fan for an ajustable on time. Maybe, 20 minutes of the fan not operating, the fan is operated for 5 minutes. You set the time off and on. If the fan cycles with heating/cooling, the fan does operate. Get fresh air alll year and maintain <50%RH during the wet time of the year. Regards TB

[tranelch]

An "Air cyclier" is an alternative to a VS furnace fan. This device has an adjustable timer that cycles the fan on schedule that monitors the fan operation. After an adjustable time of fan "off", the cyclier operates the fan for an ajustable on time. Maybe, 20 minutes of the fan not operating, the fan is operated for 5 minutes. You set the time off and on. If the fan cycles with heating/cooling, the fan does operate. Get fresh air alll year and maintain <50%RH during the wet time of the year. Regards TB

We do have the timer functionality, but if it does not coincide with the HRV are we getting much of a benefit from the HRV? Is there a way to coordinate the two?

Thanks again for your response.

[rw1995]

This fan air cyclier or timer, who makes it, model number? I'm installing a Renewaire ERV but have not purchased any controls yet. Renewaire has a FM percentage timer that sounds similar.

I believe thier timer does not account for the furnace blower run time into the timer % per hour. If I'm running the blower for heat I want the ERV to be moving air as well.

I have Geothermal and the unit run much more often and for longer periods than my old NG furnace. I would like the ERV to run when the blower runs. During the non-heating and cooling seasons, I would like to run the ERV on a percentage basis.

[beenthere]

Honeywell IAQ thermostat.

[skippedover]

It's important to understand that an ECM variable speed blower motor does not save money and may cost a lot more to run if you have undersized ducts. As the static pressure goes up, so goes the speed of the VS motor and so goes the amps driving it. Since a conventional motor would just load down with undersized ducts, the VS motor will continue to use more amps in an attempt to overcome the duct restrictions and deliver the required CFM.

On the other hand, if you know your ducts are properly sized, then the ECM VS motor will save you a ton of money in operation. Furthermore, when you select the blower to constant operation and the furnace is not being called to work, the motor will slow way, way down to where you hardly know it's running and will do a superior job of IAQ treatment and/or moving cooler air (cooler than what comes out of the furnace plenum when its running) throughout the home without creating a lot of unsavory drafts.

To answer your question directly, as long as the ducts are properly sized and the furnace is properly sized (they did a Manual 'J' load calculation before sizing the furnace, right???) I'd recommend the 90% w/ECM VS over the 95% with a standar motor. Also, be advised that there are both variable speed and fixed speed ECM motors. Be sure which you are purchasing.

[motoguy128]

With 2 other fuel sources, I'm a 90% furnace might not even have a payback over an 80% unless it's a large house and your in a northern climate. Otherwise it's not used enough to get a payback. Use your gas and electric bills to determine what your savings would be between both units.